draft-ietf-tsvwg-transport-encrypt-20.txt   draft-ietf-tsvwg-transport-encrypt-21.txt 
TSVWG G. Fairhurst TSVWG G. Fairhurst
Internet-Draft University of Aberdeen Internet-Draft University of Aberdeen
Intended status: Informational C. Perkins Intended status: Informational C. Perkins
Expires: September 9, 2021 University of Glasgow Expires: October 20, 2021 University of Glasgow
March 8, 2021 April 18, 2021
Considerations around Transport Header Confidentiality, Network Considerations around Transport Header Confidentiality, Network
Operations, and the Evolution of Internet Transport Protocols Operations, and the Evolution of Internet Transport Protocols
draft-ietf-tsvwg-transport-encrypt-20 draft-ietf-tsvwg-transport-encrypt-21
Abstract Abstract
To protect user data and privacy, Internet transport protocols have To protect user data and privacy, Internet transport protocols have
supported payload encryption and authentication for some time. Such supported payload encryption and authentication for some time. Such
encryption and authentication is now also starting to be applied to encryption and authentication is now also starting to be applied to
the transport protocol headers. This helps avoid transport protocol the transport protocol headers. This helps avoid transport protocol
ossification by middleboxes, mitigate attacks against the transport ossification by middleboxes, mitigate attacks against the transport
protocol, and protect metadata about the communication. Current protocol, and protect metadata about the communication. Current
operational practice in some networks inspect transport header operational practice in some networks inspect transport header
skipping to change at page 1, line 44 skipping to change at page 1, line 44
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 9, 2021. This Internet-Draft will expire on October 20, 2021.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Current uses of Transport Headers within the Network . . . . 4 2. Current uses of Transport Headers within the Network . . . . 4
2.1. To Identify Transport Protocols and Flows . . . . . . . . 5 2.1. To Separate Flows in Network Devices . . . . . . . . . . 5
2.2. To Understand Transport Protocol Performance . . . . . . 6 2.2. To Identify Transport Protocols and Flows . . . . . . . . 5
2.3. To Support Network Operations . . . . . . . . . . . . . . 12 2.3. To Understand Transport Protocol Performance . . . . . . 6
2.4. To Support Header Compression . . . . . . . . . . . . . . 17 2.4. To Support Network Operations . . . . . . . . . . . . . . 13
2.5. To Verify SLA Compliance . . . . . . . . . . . . . . . . 18 2.5. To Mitigate the Effects of Constrained Networks . . . . . 18
3. Research, Development and Deployment . . . . . . . . . . . . 18 2.6. To Verify SLA Compliance . . . . . . . . . . . . . . . . 19
3.1. Independent Measurement . . . . . . . . . . . . . . . . . 19 3. Research, Development and Deployment . . . . . . . . . . . . 20
3.2. Measurable Transport Protocols . . . . . . . . . . . . . 19 3.1. Independent Measurement . . . . . . . . . . . . . . . . . 20
3.3. Other Sources of Information . . . . . . . . . . . . . . 21 3.2. Measurable Transport Protocols . . . . . . . . . . . . . 21
4. Encryption and Authentication of Transport Headers . . . . . 21 3.3. Other Sources of Information . . . . . . . . . . . . . . 22
5. Intentionally Exposing Transport Information to the Network . 26 4. Encryption and Authentication of Transport Headers . . . . . 23
5.1. Exposing Transport Information in Extension Headers . . . 26 5. Intentionally Exposing Transport Information to the Network . 28
5.2. Common Exposed Transport Information . . . . . . . . . . 27 5.1. Exposing Transport Information in Extension Headers . . . 28
5.3. Considerations for Exposing Transport Information . . . . 27 5.2. Common Exposed Transport Information . . . . . . . . . . 29
5.3. Considerations for Exposing Transport Information . . . . 29
6. Addition of Transport OAM Information to Network-Layer 6. Addition of Transport OAM Information to Network-Layer
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.1. Use of OAM within a Maintenance Domain . . . . . . . . . 28 6.1. Use of OAM within a Maintenance Domain . . . . . . . . . 30
6.2. Use of OAM across Multiple Maintenance Domains . . . . . 28 6.2. Use of OAM across Multiple Maintenance Domains . . . . . 30
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 28 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 31
8. Security Considerations . . . . . . . . . . . . . . . . . . . 31 8. Security Considerations . . . . . . . . . . . . . . . . . . . 34
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36
11. Informative References . . . . . . . . . . . . . . . . . . . 34 11. Informative References . . . . . . . . . . . . . . . . . . . 36
Appendix A. Revision information . . . . . . . . . . . . . . . . 43 Appendix A. Revision information . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49
1. Introduction 1. Introduction
The transport layer supports the end-to-end flow of data across a The transport layer supports the end-to-end flow of data across a
network path, providing features such as connection establishment, network path, providing features such as connection establishment,
reliability, framing, ordering, congestion control, flow control, reliability, framing, ordering, congestion control, flow control,
etc., as needed to support applications. One of the core functions etc., as needed to support applications. One of the core functions
of an Internet transport: to discover and adapt to the of an Internet transport is to discover and adapt to the
characteristics of the network path that is currently being used. characteristics of the network path that is currently being used.
For some years, it has been common for the transport layer payload to For some years, it has been common for the transport layer payload to
be protected by encryption and authentication, but for the transport be protected by encryption and authentication, but for the transport
layer headers to be sent unprotected. Examples of protocols that layer headers to be sent unprotected. Examples of protocols that
behave in this manner include Transport Layer Security (TLS) over TCP behave in this manner include Transport Layer Security (TLS) over TCP
[RFC8446], Datagram TLS [RFC6347] [I-D.ietf-tls-dtls13], the Secure [RFC8446], Datagram TLS [RFC6347] [I-D.ietf-tls-dtls13], the Secure
Real-time Transport Protocol [RFC3711], and tcpcrypt [RFC8548]. The Real-time Transport Protocol [RFC3711], and tcpcrypt [RFC8548]. The
use of unencrypted transport headers has led some network operators, use of unencrypted transport headers has led some network operators,
researchers, and others to develop tools and processes that rely on researchers, and others to develop tools and processes that rely on
observations of transport headers both in aggregate and at the flow observations of transport headers both in aggregate and at the flow
level to infer details of the network's behaviour and inform level to infer details of the network's behaviour and inform
operational practice. operational practice.
Transport protocols are now being developed that encrypt some or all Transport protocols are now being developed that encrypt some or all
of the transport headers, in addition to the transport payload data. of the transport headers, in addition to the transport payload data.
The QUIC transport protocol [I-D.ietf-quic-transport] is an example The QUIC transport protocol [I-D.ietf-quic-transport] is an example
of such a protocol. Such transport header encryption makes it of such a protocol. Such transport header encryption makes it
difficult to observe transport protocol behaviour within the network. difficult to observe transport protocol behaviour from the vantage
This document discusses some implications of transport header point of the network. This document discusses some implications of
encryption for network operators, researchers, and others that have transport header encryption for network operators and researchers
previously observed transport headers, and highlights some issues to that have previously observed transport headers, and highlights some
consider for transport protocol designers. issues to consider for transport protocol designers.
As discussed in [RFC7258], the IETF has concluded that Pervasive As discussed in [RFC7258], the IETF has concluded that Pervasive
Monitoring (PM) is a technical attack that needs to be mitigated in Monitoring (PM) is a technical attack that needs to be mitigated in
the design of IETF protocols. This document supports that the design of IETF protocols. This document supports that
conclusion. It also recognises that RFC7258 states "Making networks conclusion. It also recognises that RFC7258 states "Making networks
unmanageable to mitigate PM is not an acceptable outcome, but unmanageable to mitigate PM is not an acceptable outcome, but
ignoring PM would go against the consensus documented here. An ignoring PM would go against the consensus documented here. An
appropriate balance will emerge over time as real instances of this appropriate balance will emerge over time as real instances of this
tension are considered". This document is written to provide input tension are considered". This document is written to provide input
to the discussion around what is an appropriate balance, by to the discussion around what is an appropriate balance, by
highlighting some implications of transport header encryption. highlighting some implications of transport header encryption.
Current uses of transport header information in the network are Current uses of transport header information by network devices on
explained, which can be beneficial or malicious. This is written to the Internet path are explained. These uses can be beneficial or
provide input to the discussion around what is an appropriate malicious. This is written to provide input to the discussion around
balance, by highlighting some implications of transport header what is an appropriate balance, by highlighting some implications of
encryption. transport header encryption.
2. Current uses of Transport Headers within the Network 2. Current uses of Transport Headers within the Network
In response to pervasive monitoring [RFC7624] revelations and the In response to pervasive monitoring [RFC7624] revelations and the
IETF consensus that "Pervasive Monitoring is an Attack" [RFC7258], IETF consensus that "Pervasive Monitoring is an Attack" [RFC7258],
efforts are underway to increase encryption of Internet traffic. efforts are underway to increase encryption of Internet traffic.
Applying confidentiality to transport header fields can improve Applying confidentiality to transport header fields can improve
privacy, and can help to mitigate certain attacks or manipulation of privacy, and can help to mitigate certain attacks or manipulation of
packets in the network, but it can also affect network operations and packets by devices on the network path, but it can also affect
measurement [RFC8404]. network operations and measurement [RFC8404].
When considering what parts of the transport headers should be When considering what parts of the transport headers should be
encrypted to provide confidentiality, and what parts should be encrypted to provide confidentiality, and what parts should be
visible to the network (including non-encrypted but authenticated visible to network devices (including non-encrypted but authenticated
headers), it is necessary to consider both the impact on network headers), it is necessary to consider both the impact on network
operations and management, and the implications for ossification and operations and management, and the implications for ossification and
user privacy [Measurement]. Different parties will view the relative user privacy [Measurement]. Different parties will view the relative
importance of these concerns differently. For some, the benefits of importance of these concerns differently. For some, the benefits of
encrypting all the transport headers outweigh the impact of doing so; encrypting all the transport headers outweigh the impact of doing so;
others might analyse the security, privacy, and ossification impacts others might analyse the security, privacy, and ossification impacts
and arrive at a different trade-off. and arrive at a different trade-off.
This section reviews examples of the observation of transport layer This section reviews examples of the observation of transport layer
headers within the network. Unencrypted transport headers provide headers within the network by devices on the network path, or using
information can support network operations and management, and this information exported by an on-path device. Unencrypted transport
section notes some ways in which this has been done. Unencrypted headers provide information that can support network operations and
transport header information also contributes metadata that can be management, and this section notes some ways in which this has been
exploited for purposes unrelated to network transport measurement, done. Unencrypted transport header information also contributes
diagnostics or troubleshooting (e.g., to block or to throttle traffic metadata that can be exploited for purposes unrelated to network
from a specific content provider), and this section also notes some transport measurement, diagnostics or troubleshooting (e.g., to block
threats relating to unencrypted transport headers. or to throttle traffic from a specific content provider), and this
section also notes some threats relating to unencrypted transport
headers.
Exposed transport information also provides a source of information Exposed transport information also provides a source of information
that contributes to linked data sets, which could be exploited to that contributes to linked data sets, which could be exploited to
deduce private information, e.g., user patterns, user location, deduce private information, e.g., user patterns, user location,
tracking behaviour, etc. This might reveal information the parties tracking behaviour, etc. This might reveal information the parties
did not intend to be revealed. [RFC6973] aims to make designers, did not intend to be revealed. [RFC6973] aims to make designers,
implementers, and users of Internet protocols aware of privacy- implementers, and users of Internet protocols aware of privacy-
related design choices in IETF protocols. related design choices in IETF protocols.
This section does not consider intentional modification of transport This section does not consider intentional modification of transport
headers by middleboxes, such as in Network Address Translation (NAT) headers by middleboxes, such as devices performing Network Address
or Firewalls. Common issues concerning IP address sharing are Translation (NAT) or Firewalls.
described in [RFC6269].
2.1. To Identify Transport Protocols and Flows 2.1. To Separate Flows in Network Devices
Some network layer mechanisms separate network traffic by flow,
without resorting to identifying the type of traffic. Hash-based
load-sharing sharing across paths (e..g., equal cost multi path,
ECMP), sharing across a group of links (e.g., using a link
aggregation group, LAG), ensuring equal access to link capacity
(e.g., fair queuing, FQ), or distributing traffic to servers (e.g.,
load balancing). To prevent packet reordering, forwarding engines
can consistently forward the same transport flows along the same
forwarding path, often achieved by calculating a hash using an
n-tuple gleaned from a combination of link header information through
to transport header information. This n-tuple can use the MAC
address, IP addresses, and can include observable transport header
information.
When transport header information cannot be observed, there can be
less information to separate flows at equipment along the path. Flow
separation might not be possible when, a transport that forms traffic
into an encrypted aggregate. For IPv6, the Flow Label [RFC6437] can
be used even when all transport information is encrypted, enabling
Flow Label-based ECMP [RFC6438] and Load-Sharing [RFC7098].
2.2. To Identify Transport Protocols and Flows
Information in exposed transport layer headers can be used by the Information in exposed transport layer headers can be used by the
network to identify transport protocols and flows [RFC8558]. The network to identify transport protocols and flows [RFC8558]. The
ability to identify transport protocols, flows, and sessions is a ability to identify transport protocols, flows, and sessions is a
common function performed, for example, by measurement activities, common function performed, for example, by measurement activities,
Quality of Service (QoS) classifiers, and firewalls. These functions Quality of Service (QoS) classifiers, and firewalls. These functions
can be beneficial, and performed with the consent of, and in support can be beneficial, and performed with the consent of, and in support
of, the end user. Alternatively, the same mechanisms could be used of, the end user. Alternatively, the same mechanisms could be used
to support practises that might be adversarial to the end user, to support practises that might be adversarial to the end user,
including blocking, de-prioritising, and monitoring traffic without including blocking, de-prioritising, and monitoring traffic without
consent. consent.
Observable transport header information, together with information in Observable transport header information, together with information in
the network header, has been used to identify flows and their the network header, has been used to identify flows and their
connection state, together with the set of protocol options being connection state, together with the set of protocol options being
used. Transport protocols, such as TCP and the Stream Control used. Transport protocols, such as TCP [RFC7414] and the Stream
Transport Protocol (SCTP), specify a standard base header that Control Transport Protocol (SCTP) [RFC4960], specify a standard base
includes sequence number information and other data. They also have header that includes sequence number information and other data.
the possibility to negotiate additional headers at connection setup, They also have the possibility to negotiate additional headers at
identified by an option number in the transport header. connection setup, identified by an option number in the transport
header.
In some uses, an assigned transport port (e.g., 0..49151) can In some uses, an assigned transport port (e.g., 0..49151) can
identify the upper-layer protocol or service [RFC7605]. However, identify the upper-layer protocol or service [RFC7605]. However,
port information alone is not sufficient to guarantee identification. port information alone is not sufficient to guarantee identification.
Applications can use arbitrary ports and do not need to use assigned Applications can use arbitrary ports and do not need to use assigned
port numbers. The use of an assigned port number is also not limited port numbers. The use of an assigned port number is also not limited
to the protocol for which the port is intended. Multiple sessions to the protocol for which the port is intended. Multiple sessions
can also be multiplexed on a single port, and ports can be re-used by can also be multiplexed on a single port, and ports can be re-used by
subsequent sessions. subsequent sessions.
Some flows can be identified by observing signalling data (e.g., Some flows can be identified by observing signalling data (e.g.,
[RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of magic [RFC3261], [RFC8837]) or through the use of magic numbers placed in
numbers placed in the first byte(s) of a datagram payload [RFC7983]. the first byte(s) of a datagram payload [RFC7983].
When transport header information cannot be observed, this removes When transport header information cannot be observed, this removes
information that could have been used to classify flows by passive information that could have been used to classify flows by passive
observers along the path. More ambitious ways could be used to observers along the path. More ambitious ways could be used to
collect, estimate, or infer flow information, including heuristics collect, estimate, or infer flow information, including heuristics
based on the analysis of traffic patterns. For example, an operator based on the analysis of traffic patterns, such as classification of
that cannot access the Session Description Protocol (SDP) session flows relying on timing, volumes of information, and correlation
descriptions [RFC4566] to classify a flow as audio traffic, might between multiple flows. For example, an operator that cannot access
instead use (possibly less-reliable) heuristics to infer that short the Session Description Protocol (SDP) session descriptions [RFC4566]
UDP packets with regular spacing carry audio traffic. Operational to classify a flow as audio traffic, might instead use (possibly
practises aimed at inferring transport parameters are out of scope less-reliable) heuristics to infer that short UDP packets with
for this document, and are only mentioned here to recognise that regular spacing carry audio traffic. Operational practises aimed at
encryption does not prevent operators from attempting to apply inferring transport parameters are out of scope for this document,
practises that were used with unencrypted transport headers. and are only mentioned here to recognise that encryption does not
prevent operators from attempting to apply practises that were used
with unencrypted transport headers.
The IAB [RFC8546] have provided a summary of expected implications of The IAB [RFC8546] have provided a summary of expected implications of
increased encryption on network functions that use the observable increased encryption on network functions that use the observable
headers and describe the expected benefits of designs that explicitly headers and describe the expected benefits of designs that explicitly
declare protocol invariant header information that can be used for declare protocol invariant header information that can be used for
this purpose. this purpose.
2.2. To Understand Transport Protocol Performance 2.3. To Understand Transport Protocol Performance
This subsection describes use by the network of exposed transport This subsection describes use by the network of exposed transport
layer headers to understand transport protocol performance and layer headers to understand transport protocol performance and
behaviour. behaviour.
2.2.1. Using Information Derived from Transport Layer Headers 2.3.1. Using Information Derived from Transport Layer Headers
Observable transport headers enable explicit measurement and analysis Observable transport headers enable explicit measurement and analysis
of protocol performance, and network anomalies at any point along the of protocol performance, and detection of network anomalies at any
Internet path. Some operators use passive monitoring to manage their point along the Internet path. Some operators use passive monitoring
portion of the Internet by characterising the performance of link/ to manage their portion of the Internet by characterising the
network segments. Inferences from transport headers are used to performance of link/network segments. Inferences from transport
derive performance metrics: headers are used to derive performance metrics:
Traffic Rate and Volume: Volume measures per-application can be used Traffic Rate and Volume: Per-application traffic rate and volume
to characterise the traffic that uses a network segment or the measures can be used to characterise the traffic that uses a
pattern of network usage. Observing the protocol sequence number network segment or the pattern of network usage. Observing the
and packet size offers one way to measure this (e.g., measurements protocol sequence number and packet size offers one way to measure
observing counters in periodic reports such as RTCP; or this (e.g., measurements observing counters in periodic reports
measurements observing protocol sequence numbers in statistical such as RTCP; or measurements observing protocol sequence numbers
samples of packet flows, or specific control packets, such as in statistical samples of packet flows, or specific control
those observed at the start and end of a flow). packets, such as those observed at the start and end of a flow).
Measurements can be per endpoint, or for an endpoint aggregate. Measurements can be per endpoint, or for an endpoint aggregate.
These could be used to assess usage or for subscriber billing. These could be used to assess usage or for subscriber billing.
Such measurements can be used to trigger traffic shaping, and to Such measurements can be used to trigger traffic shaping, and to
associate QoS support within the network and lower layers. This associate QoS support within the network and lower layers. This
can be done with consent and in support of an end user, to improve can be done with consent and in support of an end user, to improve
quality of service; or could be used by the network to de- quality of service; or could be used by the network to de-
prioritise certain flows without user consent. prioritise certain flows without user consent.
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Network operators have used the variation in patterns to detect Network operators have used the variation in patterns to detect
changes in the offered service. Understanding the location and changes in the offered service. Understanding the location and
root cause of loss can help an operator determine whether this root cause of loss can help an operator determine whether this
requires corrective action. requires corrective action.
There are various causes of loss, including: corruption of link There are various causes of loss, including: corruption of link
frames (e.g., due to interference on a radio link), buffering loss frames (e.g., due to interference on a radio link), buffering loss
(e.g., overflow due to congestion, Active Queue Management, AQM (e.g., overflow due to congestion, Active Queue Management, AQM
[RFC7567], or inadequate provision following traffic pre-emption), [RFC7567], or inadequate provision following traffic pre-emption),
and policing (traffic management [RFC2475]). Understanding flow and policing (traffic management [RFC2475]). Understanding flow
loss rates requires either observing sequence numbers in network loss rates requires maintaining per-flow state (flow
or transport headers, or maintaining per-flow packet counters identification often requires transport layer information) and
(flow identification often requires transport layer information). either observing the increase in sequence numbers in the network
Per-hop loss can also sometimes be monitored at the interface or transport headers, or comparing a per-flow packet counter with
level by devices in the network. the number of packets that the flow actually sent. Per-hop loss
can also sometimes be monitored at the interface level by devices
on the network path, or using in-situ methods operating over a
network segment (see Section 3.3).
The pattern of loss can provide insight into the cause of loss. The pattern of loss can provide insight into the cause of loss.
Losses can often occur as bursts, randomly-timed events, etc. It Losses can often occur as bursts, randomly-timed events, etc. It
can also be valuable to understand the conditions under which loss can also be valuable to understand the conditions under which loss
occurs. This usually requires relating loss to the traffic occurs. This usually requires relating loss to the traffic
flowing at a network node or segment at the time of loss. flowing at a network node or segment at the time of loss.
Transport header information can help identify cases where loss Transport header information can help identify cases where loss
could have been wrongly identified, or where the transport did not could have been wrongly identified, or where the transport did not
require transmission of a lost packet. require retransmission of a lost packet.
Throughput and Goodput: Throughput is the amount of payload data Throughput and Goodput: Throughput is the amount of payload data
sent by a flow per time interval. Goodput (see Section 2.5 of sent by a flow per time interval. Goodput (the subset of
[RFC7928]) is a measure of useful data exchanged (the ratio of throughput consisting of useful traffic) (see Section 2.5 of
useful data to total volume of traffic sent by a flow). The [RFC7928] and [RFC5166]) is a measure of useful data exchanged.
throughput of a flow can be determined in the absence of transport The throughput of a flow can be determined in the absence of
header information, providing that the individual flow can be transport header information, providing that the individual flow
identified, and the overhead known. Goodput requires ability to can be identified, and the overhead known. Goodput requires
differentiate loss and retransmission of packets, for example by ability to differentiate loss and retransmission of packets, for
observing packet sequence numbers in the TCP or RTP headers example by observing packet sequence numbers in the TCP or RTP
[RFC3550]. headers [RFC3550].
Latency: Latency is a key performance metric that impacts Latency: Latency is a key performance metric that impacts
application and user-perceived response times. It often application and user-perceived response times. It often
indirectly impacts throughput and flow completion time. This indirectly impacts throughput and flow completion time. This
determines the reaction time of the transport protocol itself, determines the reaction time of the transport protocol itself,
impacting flow setup, congestion control, loss recovery, and other impacting flow setup, congestion control, loss recovery, and other
transport mechanisms. The observed latency can have many transport mechanisms. The observed latency can have many
components [Latency]. Of these, unnecessary/unwanted queueing in components [Latency]. Of these, unnecessary/unwanted queueing in
network buffers has often been observed as a significant factor buffers of the network devices on the path has often been observed
[bufferbloat]. Once the cause of unwanted latency has been as a significant factor [bufferbloat]. Once the cause of unwanted
identified, this can often be eliminated. latency has been identified, this can often be eliminated.
To measure latency across a part of a path, an observation point To measure latency across a part of a path, an observation point
[RFC7799] can measure the experienced round trip time (RTT) using [RFC7799] can measure the experienced round trip time (RTT) using
packet sequence numbers and acknowledgements, or by observing packet sequence numbers and acknowledgements, or by observing
header timestamp information. Such information allows an header timestamp information. Such information allows an
observation point in the network to determine not only the path observation point on the network path to determine not only the
RTT, but also allows measurement of the upstream and downstream path RTT, but also allows measurement of the upstream and
contribution to the RTT. This could be used to locate a source of downstream contribution to the RTT. This could be used to locate
latency, e.g., by observing cases where the median RTT is much a source of latency, e.g., by observing cases where the median RTT
greater than the minimum RTT for a part of a path. is much greater than the minimum RTT for a part of a path.
The service offered by network operators can benefit from latency The service offered by network operators can benefit from latency
information to understand the impact of configuration changes and information to understand the impact of configuration changes and
to tune deployed services. Latency metrics are key to evaluating to tune deployed services. Latency metrics are key to evaluating
and deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit and deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit
Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements
could identify excessively large buffers, indicating where to could identify excessively large buffers, indicating where to
deploy or configure AQM. An AQM method is often deployed in deploy or configure AQM. An AQM method is often deployed in
combination with other techniques, such as scheduling [RFC7567] combination with other techniques, such as scheduling [RFC7567]
[RFC8290] and although parameter-less methods are desired [RFC8290] and although parameter-less methods are desired
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[RFC8289] [RFC8033] because they cannot scale across all possible [RFC8289] [RFC8033] because they cannot scale across all possible
deployment scenarios. deployment scenarios.
Latency and round-trip time information can potentially expose Latency and round-trip time information can potentially expose
some information useful for approximate geolocation, as discussed some information useful for approximate geolocation, as discussed
in [PAM-RTT]. in [PAM-RTT].
Variation in delay: Some network applications are sensitive to Variation in delay: Some network applications are sensitive to
(small) changes in packet timing (jitter). Short and long-term (small) changes in packet timing (jitter). Short and long-term
delay variation can impact on the latency of a flow and hence the delay variation can impact on the latency of a flow and hence the
perceived quality of applications using the network. For example, perceived quality of applications using a network path. For
jitter metrics are often cited when characterising paths example, jitter metrics are often cited when characterising paths
supporting real-time traffic. The expected performance of such supporting real-time traffic. The expected performance of such
applications, can be inferred from a measure the variation in applications, can be inferred from a measure of the variation in
delay observed along a portion of the path [RFC3393] [RFC5481]. delay observed along a portion of the path [RFC3393] [RFC5481].
The requirements resemble those for the measurement of latency. The requirements resemble those for the measurement of latency.
Flow Reordering: Significant packet reordering within a flow can Flow Reordering: Significant packet reordering within a flow can
impact time-critical applications and can be interpreted as loss impact time-critical applications and can be interpreted as loss
by reliable transports. Many transport protocol techniques are by reliable transports. Many transport protocol techniques are
impacted by reordering (e.g., triggering TCP retransmission or re- impacted by reordering (e.g., triggering TCP retransmission or re-
buffering of real-time applications). Packet reordering can occur buffering of real-time applications). Packet reordering can occur
for many reasons, from equipment design to misconfiguration of for many reasons, from equipment design to misconfiguration of
forwarding rules. Flow identification is often required to avoid forwarding rules. Flow identification is often required to avoid
significant packet mis-ordering (e.g., when ECMP is used). significant packet mis-ordering (e.g., when using ECMP, or LAG).
Network tools can detect and measure unwanted/excessive Network tools can detect and measure unwanted/excessive
reordering, and the impact on transport performance. reordering, and the impact on transport performance.
There have been initiatives in the IETF transport area to reduce There have been initiatives in the IETF transport area to reduce
the impact of reordering within a transport flow, possibly leading the impact of reordering within a transport flow, possibly leading
to a reduction in the requirements for preserving ordering. These to a reduction in the requirements for preserving ordering. These
have potential to simplify network equipment design as well as the have potential to simplify network equipment design as well as the
potential to improve robustness of the transport service. potential to improve robustness of the transport service.
Measurements of reordering can help understand the present level Measurements of reordering can help understand the present level
of reordering, and inform decisions about how to progress new of reordering, and inform decisions about how to progress new
mechanisms. mechanisms.
Techniques for measuring reordering typically observe packet Techniques for measuring reordering typically observe packet
sequence numbers. Metrics have been defined that evaluate whether sequence numbers. Metrics have been defined that evaluate whether
a network has maintained packet order on a packet-by-packet basis a network path has maintained packet order on a packet-by-packet
[RFC4737] [RFC5236]. Some protocols provide in-built monitoring basis [RFC4737] [RFC5236]. Some protocols provide in-built
and reporting functions. Transport fields in the RTP header monitoring and reporting functions. Transport fields in the RTP
[RFC3550] [RFC4585] can be observed to derive traffic volume header [RFC3550] [RFC4585] can be observed to derive traffic
measurements and provide information on the progress and quality volume measurements and provide information on the progress and
of a session using RTP. Metadata assists in understanding the quality of a session using RTP. Metadata assists in understanding
context under which the data was collected, including the time, the context under which the data was collected, including the
observation point [RFC7799], and way in which metrics were time, observation point [RFC7799], and way in which metrics were
accumulated. The RTCP protocol directly reports some of this accumulated. The RTCP protocol directly reports some of this
information in a form that can be directly visible in the network. information in a form that can be directly visible by devices on
the network path.
In some cases, measurements could involve active injection of test In some cases, measurements could involve active injection of test
traffic to perform a measurement (see Section 3.4 of [RFC7799]). traffic to perform a measurement (see Section 3.4 of [RFC7799]).
However, most operators do not have access to user equipment, However, most operators do not have access to user equipment,
therefore the point of test is normally different from the transport therefore the point of test is normally different from the transport
endpoint. Injection of test traffic can incur an additional cost in endpoint. Injection of test traffic can incur an additional cost in
running such tests (e.g., the implications of capacity tests in a running such tests (e.g., the implications of capacity tests in a
mobile network are obvious). Some active measurements [RFC7799] mobile network segment are obvious). Some active measurements
(e.g., response under load or particular workloads) perturb other [RFC7799] (e.g., response under load or particular workloads) perturb
traffic, and could require dedicated access to the network segment. other traffic, and could require dedicated access to the network
segment.
Passive measurements (see Section 3.6 of [RFC7799]) can have Passive measurements (see Section 3.6 of [RFC7799]) can have
advantages in terms of eliminating unproductive test traffic, advantages in terms of eliminating unproductive test traffic,
reducing the influence of test traffic on the overall traffic mix, reducing the influence of test traffic on the overall traffic mix,
and the ability to choose the point of observation (see and the ability to choose the point of observation (see
Section 2.3.1). Measurements can rely on observing packet headers, Section 2.4.1). Measurements can rely on observing packet headers,
which is not possible if those headers are encrypted, but could which is not possible if those headers are encrypted, but could
utilise information about traffic volumes or patterns of interaction utilise information about traffic volumes or patterns of interaction
to deduce metrics. to deduce metrics.
Passive packet sampling techniques are also often used to scale the Passive packet sampling techniques are also often used to scale the
processing involved in observing packets on high rate links. This processing involved in observing packets on high rate links. This
exports only the packet header information of (randomly) selected exports only the packet header information of (randomly) selected
packets. Interpretation of the exported information relies on packets. Interpretation of the exported information relies on
understanding of the header information. The utility of these understanding of the header information. The utility of these
measurements depends on the type of bearer and number of mechanisms measurements depends on the type of network segment/link and number
used by network devices. Simple routers are relatively easy to of mechanisms used by the network devices. Simple routers are
manage, but a device with more complexity demands understanding of relatively easy to manage, but a device with more complexity demands
the choice of many system parameters. understanding of the choice of many system parameters.
2.2.2. Using Information Derived from Network Layer Header Fields 2.3.2. Using Information Derived from Network Layer Header Fields
Information from the transport header can be used by a multi-field Information from the transport header can be used by a multi-field
(MF) classifier as a part of policy framework. Policies are commonly (MF) classifier as a part of policy framework. Policies are commonly
used for management of the QoS or Quality of Experience (QoE) in used for management of the QoS or Quality of Experience (QoE) in
resource-constrained networks, or by firewalls to implement access resource-constrained networks, or by firewalls to implement access
rules (see also Section 2.2.2 of [RFC8404]). Policies can support rules (see also Section 2.2.2 of [RFC8404]). Policies can support
user applications/services or protect against unwanted, or lower user applications/services or protect against unwanted, or lower
priority traffic (Section 2.3.4). priority traffic (Section 2.4.4).
Transport layer information can also be explicitly carried in Transport layer information can also be explicitly carried in
network-layer header fields that are not encrypted, serving as a network-layer header fields that are not encrypted, serving as a
replacement/addition to the exposed transport header information replacement/addition to the exposed transport header information
[RFC8558]. This information can enable a different forwarding [RFC8558]. This information can enable a different forwarding
treatment by the network, even when a transport employs encryption to treatment by the devices forming the network path, even when a
protect other header information. transport employs encryption to protect other header information.
On the one hand, the user of a transport that multiplexes multiple On the one hand, the user of a transport that multiplexes multiple
sub-flows might want to obscure the presence and characteristics of sub-flows might want to obscure the presence and characteristics of
these sub-flows. On the other hand, an encrypted transport could set these sub-flows. On the other hand, an encrypted transport could set
the network-layer information to indicate the presence of sub-flows, the network-layer information to indicate the presence of sub-flows,
and to reflect the service requirements of individual sub-flows. and to reflect the service requirements of individual sub-flows.
There are several ways this could be done: There are several ways this could be done:
IP Address: Applications normally expose the endpoint addresses used IP Address: Applications normally expose the endpoint addresses used
in the forwarding decisions in network devices. Address and other in the forwarding decisions in network devices. Address and other
protocol information can be used by a MF-classifier to determine protocol information can be used by a MF-classifier to determine
how traffic is treated [RFC2475], and hence affect the quality of how traffic is treated [RFC2475], and hence affect the quality of
experience for a flow. experience for a flow. Common issues concerning IP address
sharing are described in [RFC6269].
Using the IPv6 Network-Layer Flow Label: A number of Standards Track Using the IPv6 Network-Layer Flow Label: A number of Standards Track
and Best Current Practice RFCs (e.g., [RFC8085], [RFC6437], and Best Current Practice RFCs (e.g., [RFC8085], [RFC6437],
[RFC6438]) encourage endpoints to set the IPv6 flow label field of [RFC6438]) encourage endpoints to set the IPv6 flow label field of
the network-layer header. IPv6 "source nodes SHOULD assign each the network-layer header. IPv6 "source nodes SHOULD assign each
unrelated transport connection and application data stream to a unrelated transport connection and application data stream to a
new flow" [RFC6437]. A multiplexing transport could choose to use new flow" [RFC6437]. A multiplexing transport could choose to use
multiple flow labels to allow the network to independently forward multiple flow labels to allow the network to independently forward
sub-flows. RFC6437 provides further guidance on choosing a flow sub-flows. RFC6437 provides further guidance on choosing a flow
label value, stating these "should be chosen such that their bits label value, stating these "should be chosen such that their bits
exhibit a high degree of variability", and chosen so that "third exhibit a high degree of variability", and chosen so that "third
parties should be unlikely to be able to guess the next value that parties should be unlikely to be able to guess the next value that
a source of flow labels will choose". a source of flow labels will choose".
Once set, a flow label can provide information that can help Once set, a flow label can provide information that can help
inform network-layer queueing and forwarding [RFC6438], for inform network-layer queueing and forwarding, including use with
example with Equal Cost Multi-Path routing and Link Aggregation IPsec, [RFC6294] and use with Equal Cost Multi-Path routing and
[RFC6294]. RFC 6438 describes considerations when using IPsec Link Aggregation[RFC6438].
[RFC6438].
The choice of how to assign a flow label needs to avoid The choice of how to assign a flow label needs to avoid
introducing linkability that a network device could observe. introducing linkages between flows that a network device could not
Inappropriate use by the transport can have privacy implications otherwise observe. Inappropriate use by the transport can have
(e.g., assigning the same label to two independent flows that privacy implications (e.g., assigning the same label to two
ought not to be classified the same). independent flows that ought not to be classified the same).
Using the Network-Layer Differentiated Services Code Point: Using the Network-Layer Differentiated Services Code Point:
Applications can expose their delivery expectations to the network Applications can expose their delivery expectations to network
by setting the Differentiated Services Code Point (DSCP) field of devices by setting the Differentiated Services Code Point (DSCP)
IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications field of IPv4 and IPv6 packets [RFC2474]. For example, WebRTC
identify different forwarding treatments for individual sub-flows applications identify different forwarding treatments for
(audio vs. video) based on the value of the DSCP field individual sub-flows (audio vs. video) based on the value of the
[I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information DSCP field [I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit
to inform network-layer queueing and forwarding, rather than an information to inform network-layer queueing and forwarding,
operator inferring traffic requirements from transport and rather than an operator inferring traffic requirements from
application headers via a multi-field classifier. Inappropriate transport and application headers via a multi-field classifier.
use by the transport can have privacy implications (e.g., Inappropriate use by the transport can have privacy implications
assigning a different DSCP to a subflow could assist in a network (e.g., assigning a different DSCP to a subflow could assist in a
device discovering the traffic pattern used by an application, network device discovering the traffic pattern used by an
assigning the same label to two independent flows that ought not application). The field is mutable, i.e., some network devices
to be classified the same). The field is mutable, i.e., some can be expected to change this field. Since the DSCP value can
network devices can be expected to change this field. Since the impact the quality of experience for a flow, observations of
DSCP value can impact the quality of experience for a flow, service performance have to consider this field when a network
observations of service performance have to consider this field path supports differentiated service treatment.
when a network path supports differentiated service treatment.
Using Explicit Congestion Marking: ECN [RFC3168] is a transport Using Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that uses the ECN field in the network-layer header. mechanism that uses the ECN field in the network-layer header.
Use of ECN explicitly informs the network-layer that a transport Use of ECN explicitly informs the network-layer that a transport
is ECN-capable, and requests ECN treatment of the flow. An ECN- is ECN-capable, and requests ECN treatment of the flow. An ECN-
capable transport can offer benefits when used over a path with capable transport can offer benefits when used over a path with
equipment that implements an AQM method with CE marking of IP equipment that implements an AQM method with CE marking of IP
packets [RFC8087], since it can react to congestion without also packets [RFC8087], since it can react to congestion without also
having to recover from lost packets. having to recover from lost packets.
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and transport behaviour as the use of ECN increases and new and transport behaviour as the use of ECN increases and new
methods emerge [RFC7567]. methods emerge [RFC7567].
Network-Layer Options Network protocols can carry optional headers Network-Layer Options Network protocols can carry optional headers
(see Section 5.1). These can explicitly expose transport header (see Section 5.1). These can explicitly expose transport header
information to on-path devices operating at the network layer (as information to on-path devices operating at the network layer (as
discussed further in Section 6). discussed further in Section 6).
IPv4 [RFC0791] has provision for optional header fields. IP IPv4 [RFC0791] has provision for optional header fields. IP
routers can examine these headers and are required to ignore IPv4 routers can examine these headers and are required to ignore IPv4
options that they does not recognise. Many current paths include options that they do not recognise. Many current paths include
network devices that forward packets that carry options on a network devices that forward packets that carry options on a
slower processing path. Some network devices (e.g., firewalls) slower processing path. Some network devices (e.g., firewalls)
can be (and are) configured to drop these packets [RFC7126]. BCP can be (and are) configured to drop these packets [RFC7126]. BCP
186 [RFC7126] provides Best Current Practice guidance on how 186 [RFC7126] provides Best Current Practice guidance on how
operators should treat IPv4 packets that specify options. operators should treat IPv4 packets that specify options.
IPv6 can encode optional network-layer information in separate IPv6 can encode optional network-layer information in separate
headers that may be placed between the IPv6 header and the upper- headers that may be placed between the IPv6 header and the upper-
layer header [RFC8200]. The Hop-by-Hop options header, when layer header [RFC8200]. (e.g., the IPv6 Alternate Marking Method
[I-D.ietf-6man-ipv6-alt-mark], which can be used to measure packet
loss and delay metrics). The Hop-by-Hop options header, when
present, immediately follows the IPv6 header. IPv6 permits this present, immediately follows the IPv6 header. IPv6 permits this
header to be examined by any node along the path if explicitly header to be examined by any node along the path if explicitly
configured [RFC8200]. configured [RFC8200].
Careful use of the network layer features (e.g., Extension Headers Careful use of the network layer features (e.g., Extension Headers
can Section 5) help provide similar information in the case where the can Section 5) help provide similar information in the case where the
network is unable to inspect transport protocol headers. network is unable to inspect transport protocol headers.
2.3. To Support Network Operations 2.4. To Support Network Operations
Some network operators make use of on-path observations of transport Some network operators make use of on-path observations of transport
headers to analyse the service offered to the users of a network headers to analyse the service offered to the users of a network
segment, and to inform operational practice, and can help detect and segment, and to inform operational practice, and can help detect and
locate network problems. [RFC8517] gives an operator's perspective locate network problems. [RFC8517] gives an operator's perspective
about such use. about such use.
When observable transport header information is not available, those When observable transport header information is not available, those
seeking an understanding of transport behaviour and dynamics might seeking an understanding of transport behaviour and dynamics might
learn to work without that information. Alternatively, they might learn to work without that information. Alternatively, they might
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other heuristics to infer network behaviour (see Section 2.1.1 of other heuristics to infer network behaviour (see Section 2.1.1 of
[RFC8404]). Operational practises aimed at inferring transport [RFC8404]). Operational practises aimed at inferring transport
parameters are out of scope for this document, and are only mentioned parameters are out of scope for this document, and are only mentioned
here to recognise that encryption does not necessarily stop operators here to recognise that encryption does not necessarily stop operators
from attempting to apply practises that have been used with from attempting to apply practises that have been used with
unencrypted transport headers. unencrypted transport headers.
This section discusses topics concerning observation of transport This section discusses topics concerning observation of transport
flows, with a focus on transport measurement. flows, with a focus on transport measurement.
2.3.1. Problem Location 2.4.1. Problem Location
Observations of transport header information can be used to locate Observations of transport header information can be used to locate
the source of problems or to assess the performance of a network the source of problems or to assess the performance of a network
segment. Often issues can only be understood in the context of the segment. Often issues can only be understood in the context of the
other flows that share a particular path, particular device other flows that share a particular path, particular device
configuration, interface port, etc. A simple example is monitoring configuration, interface port, etc. A simple example is monitoring
of a network device that uses a scheduler or active queue management of a network device that uses a scheduler or active queue management
technique [RFC7567], where it could be desirable to understand technique [RFC7567], where it could be desirable to understand
whether the algorithms are correctly controlling latency, or if whether the algorithms are correctly controlling latency, or if
overload protection is working. This implies knowledge of how overload protection is working. This implies knowledge of how
traffic is assigned to any sub-queues used for flow scheduling, but traffic is assigned to any sub-queues used for flow scheduling, but
can require information about how the traffic dynamics impact active can require information about how the traffic dynamics impact active
queue management, starvation prevention mechanisms, and circuit- queue management, starvation prevention mechanisms, and circuit-
breakers. breakers.
Sometimes correlating observations of headers at multiple points Sometimes correlating observations of headers at multiple points
along the path (e.g., at the ingress and egress of a network along the path (e.g., at the ingress and egress of a network
segment), allows an observer to determine the contribution of a segment), allows an observer to determine the contribution of a
portion of the path to an observed metric. e.g., to locate a source portion of the path to an observed metric. e.g., to locate a source
of delay, jitter, loss, reordering, congestion marking. of delay, jitter, loss, reordering, or congestion marking.
2.3.2. Network Planning and Provisioning 2.4.2. Network Planning and Provisioning
Traffic rate and volume measurements are used to help plan deployment Traffic rate and volume measurements are used to help plan deployment
of new equipment and configuration in networks. Data is also of new equipment and configuration in networks. Data is also
valuable to equipment vendors who want to understand traffic trends valuable to equipment vendors who want to understand traffic trends
and patterns of usage as inputs to decisions about planning products and patterns of usage as inputs to decisions about planning products
and provisioning for new deployments. and provisioning for new deployments.
Trends in aggregate traffic can be observed and can be related to the Trends in aggregate traffic can be observed and can be related to the
endpoint addresses being used, but when transport header information endpoint addresses being used, but when transport header information
is not observable, it might be impossible to correlate patterns in is not observable, it might be impossible to correlate patterns in
measurements with changes in transport protocols. This increases the measurements with changes in transport protocols. This increases the
dependency on other indirect sources of information to inform dependency on other indirect sources of information to inform
planning and provisioning. planning and provisioning.
2.3.3. Compliance with Congestion Control 2.4.3. Compliance with Congestion Control
The traffic that can be observed by on-path network devices (the The traffic that can be observed by on-path network devices (the
"wire image") is a function of transport protocol design/options, "wire image") is a function of transport protocol design/options,
network use, applications, and user characteristics. In general, network use, applications, and user characteristics. In general,
when only a small proportion of the traffic has a specific when only a small proportion of the traffic has a specific
(different) characteristic, such traffic seldom leads to operational (different) characteristic, such traffic seldom leads to operational
concern, although the ability to measure and monitor it is lower. concern, although the ability to measure and monitor it is lower.
The desire to understand the traffic and protocol interactions The desire to understand the traffic and protocol interactions
typically grows as the proportion of traffic increases in volume. typically grows as the proportion of traffic increases. The
The challenges increase when multiple instances of an evolving challenges increase when multiple instances of an evolving protocol
protocol contribute to the traffic that share network capacity. contribute to the traffic that share network capacity.
Operators can manage traffic load (e.g., when the network is severely Operators can manage traffic load (e.g., when the network is severely
overloaded) by deploying rate-limiters, traffic shaping, or network overloaded) by deploying rate-limiters, traffic shaping, or network
transport circuit breakers [RFC8084]. The information provided by transport circuit breakers [RFC8084]. The information provided by
observing transport headers is a source of data that can help to observing transport headers is a source of data that can help to
inform such mechanisms. inform such mechanisms.
Congestion Control Compliance of Traffic: Congestion control is a Congestion Control Compliance of Traffic: Congestion control is a
key transport function [RFC2914]. Many network operators key transport function [RFC2914]. Many network operators
implicitly accept that TCP traffic complies with a behaviour that implicitly accept that TCP traffic complies with a behaviour that
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critical to the stable operation of the Internet, applications and critical to the stable operation of the Internet, applications and
other protocols that choose to use UDP as a transport have to other protocols that choose to use UDP as a transport have to
employ mechanisms to prevent collapse, avoid unacceptable employ mechanisms to prevent collapse, avoid unacceptable
contributions to jitter/latency, and to establish an acceptable contributions to jitter/latency, and to establish an acceptable
share of capacity with concurrent traffic [RFC8085]. share of capacity with concurrent traffic [RFC8085].
UDP flows that expose a well-known header can be observed to gain UDP flows that expose a well-known header can be observed to gain
understanding of the dynamics of a flow and its congestion control understanding of the dynamics of a flow and its congestion control
behaviour. For example, tools exist to monitor various aspects of behaviour. For example, tools exist to monitor various aspects of
RTP header information and RTCP reports for real-time flows (see RTP header information and RTCP reports for real-time flows (see
Section 2.2). The Secure RTP and RTCP extensions [RFC3711] were Section 2.3). The Secure RTP and RTCP extensions [RFC3711] were
explicitly designed to expose some header information to enable explicitly designed to expose some header information to enable
such observation, while protecting the payload data. such observation, while protecting the payload data.
A network operator can observe the headers of transport protocols A network operator can observe the headers of transport protocols
layered above UDP to understand if the datagram flows comply with layered above UDP to understand if the datagram flows comply with
congestion control expectations. This can help inform a decision congestion control expectations. This can help inform a decision
on whether it might be appropriate to deploy methods such as rate- on whether it might be appropriate to deploy methods such as rate-
limiters to enforce acceptable usage. The available information limiters to enforce acceptable usage. The available information
determines the level of precision with which flows can be determines the level of precision with which flows can be
classified and the design space for conditioning mechanisms (e.g., classified and the design space for conditioning mechanisms (e.g.,
rate limiting, circuit breaker techniques [RFC8084], or blocking rate limiting, circuit breaker techniques [RFC8084], or blocking
of uncharacterised traffic) [RFC5218]. of uncharacterised traffic) [RFC5218].
When anomalies are detected, tools can interpret the transport header When anomalies are detected, tools can interpret the transport header
information to help understand the impact of specific transport information to help understand the impact of specific transport
protocols (or protocol mechanisms) on the other traffic that shares a protocols (or protocol mechanisms) on the other traffic that shares a
network. An observation in the network can gain an understanding of network. An observer on the network path can gain an understanding
the dynamics of a flow and its congestion control behaviour. of the dynamics of a flow and its congestion control behaviour.
Analysing observed flows can help to build confidence that an Analysing observed flows can help to build confidence that an
application flow backs-off its share of the network load under application flow backs-off its share of the network load under
persistent congestion, and hence to understand whether the behaviour persistent congestion, and hence to understand whether the behaviour
is appropriate for sharing limited network capacity. For example, it is appropriate for sharing limited network capacity. For example, it
is common to visualise plots of TCP sequence numbers versus time for is common to visualise plots of TCP sequence numbers versus time for
a flow to understand how a flow shares available capacity, deduce its a flow to understand how a flow shares available capacity, deduce its
dynamics in response to congestion, etc. dynamics in response to congestion, etc.
The ability to identify sources and flows that contribute to The ability to identify sources and flows that contribute to
persistent congestion is important to the safe operation of network persistent congestion is important to the safe operation of network
infrastructure, and can inform configuration of network devices to infrastructure, and can inform configuration of network devices to
complement the endpoint congestion avoidance mechanisms [RFC7567] complement the endpoint congestion avoidance mechanisms [RFC7567]
[RFC8084] to avoid a portion of the network being driven into [RFC8084] to avoid a portion of the network being driven into
congestion collapse [RFC2914]. congestion collapse [RFC2914].
2.3.4. To Characterise "Unknown" Network Traffic 2.4.4. To Characterise "Unknown" Network Traffic
The patterns and types of traffic that share Internet capacity change The patterns and types of traffic that share Internet capacity change
over time as networked applications, usage patterns and protocols over time as networked applications, usage patterns and protocols
continue to evolve. continue to evolve.
Encryption can increase the volume of "unknown" or "uncharacterised" Encryption can increase the volume of "unknown" or "uncharacterised"
traffic seen by the network. If these traffic patterns form a small traffic seen by the network. If these traffic patterns form a small
part of the traffic aggregate passing through a network device or part of the traffic aggregate passing through a network device or
segment of the network the path, the dynamics of the uncharacterised segment of the network path, the dynamics of the uncharacterised
traffic might not have a significant collateral impact on the traffic might not have a significant collateral impact on the
performance of other traffic that shares this network segment. Once performance of other traffic that shares this network segment. Once
the proportion of this traffic increases, monitoring the traffic can the proportion of this traffic increases, monitoring the traffic can
determine if appropriate safety measures have to be put in place. determine if appropriate safety measures have to be put in place.
Tracking the impact of new mechanisms and protocols requires traffic Tracking the impact of new mechanisms and protocols requires traffic
volume to be measured and new transport behaviours to be identified. volume to be measured and new transport behaviours to be identified.
This is especially true of protocols operating over a UDP substrate. This is especially true of protocols operating over a UDP substrate.
The level and style of encryption needs to be considered in The level and style of encryption needs to be considered in
determining how this activity is performed. On a shorter timescale, determining how this activity is performed.
information could also be collected to manage Denial of Service (DoS)
attacks against the infrastructure.
Traffic that cannot be classified, typically receives a default Traffic that cannot be classified typically receives a default
treatment. Some networks block or rate-limit traffic that cannot be treatment. Some networks block or rate-limit traffic that cannot be
classified. classified.
2.3.5. Network Diagnostics and Troubleshooting 2.4.5. To Support Network Security Functions
On-path observation of the transport headers of packets can be used
for various security functions. For example, Denial of Service (DoS)
and Distributed DoS (DDoS) attacks against the infrastructure or
against an endpoint can be detected and mitigated by characterising
anomalous traffic (see Section 2.4.4) on a shorter timescale. Other
uses include support for security audits (e.g., verifying the
compliance with cipher suites), client and application fingerprinting
for inventory, and to provide alerts for network intrusion detection
and other next generation firewall functions.
When using an encrypted transport, endpoints can directly provide
information to support these security functions. Another method, if
the endpoints do not provide this information, is to use an on-path
network device that relies on pattern inferences in the traffic, and
heuristics or machine learning instead of processing observed header
information. An endpoint could also explicitly cooperate with an on-
path device (e.g., a QUIC endpoint could share information about
current uses of connection IDs).
2.4.6. Network Diagnostics and Troubleshooting
Operators monitor the health of a network segment to support a Operators monitor the health of a network segment to support a
variety of operational tasks [RFC8404] including procedures to variety of operational tasks [RFC8404] including procedures to
provide early warning and trigger action: to diagnose network provide early warning and trigger action: to diagnose network
problems, to manage security threats (including DoS), to evaluate problems, to manage security threats (including DoS), to evaluate
equipment or protocol performance, or to respond to user performance equipment or protocol performance, or to respond to user performance
questions. Information about transport flows can assist in setting questions. Information about transport flows can assist in setting
buffer sizes, and help identify whether link/network tuning is buffer sizes, and help identify whether link/network tuning is
effective. Information can also support debugging and diagnosis of effective. Information can also support debugging and diagnosis of
the root causes of faults that concern a particular user's traffic the root causes of faults that concern a particular user's traffic
and can support post-mortem investigation after an anomaly. and can support post-mortem investigation after an anomaly.
Section 3.1.2 and Section 5 of [RFC8404] provide further examples. Section 3.1.2 and Section 5 of [RFC8404] provide further examples.
Network segments vary in their complexity. The design trade-offs for Network segments vary in their complexity. The design trade-offs for
radio networks are often very different from those of wired networks radio networks are often very different from those of wired networks
[RFC8462]. A radio-based network (e.g., cellular mobile, enterprise [RFC8462]. A radio-based network (e.g., cellular mobile, enterprise
Wireless LAN (WLAN), satellite access/back-haul, point-to-point Wireless LAN (WLAN), satellite access/back-haul, point-to-point
radio) add a subsystem that performs radio resource management, with radio) adds a subsystem that performs radio resource management, with
impact on the available capacity, and potentially loss/reordering of impact on the available capacity, and potentially loss/reordering of
packets. This impact can differ by traffic type, and can be packets. This impact can differ by traffic type, and can be
correlated with link propagation and interference. These can impact correlated with link propagation and interference. These can impact
the cost and performance of a provided service, and is expected to the cost and performance of a provided service, and is expected to
increase in importance as operators bring together heterogeneous increase in importance as operators bring together heterogeneous
types of network equipment and deploy opportunistic methods to access types of network equipment and deploy opportunistic methods to access
shared radio spectrum. shared radio spectrum.
2.3.6. Tooling and Network Operations 2.4.7. Tooling and Network Operations
A variety and open source and proprietary tools have been deployed A variety of open source and proprietary tools have been deployed
that use the transport header information observable with widely used that use the transport header information observable with widely used
protocols such as TCP or RTP/UDP/IP. Tools that dissect network protocols such as TCP or RTP/UDP/IP. Tools that dissect network
traffic flows can alert to potential problems that are hard to derive traffic flows can alert to potential problems that are hard to derive
from volume measurements, link statistics or device measurements from volume measurements, link statistics or device measurements
alone. alone.
Changes to the transport, whether to protect the transport headers, Any introduction of a new transport protocol, protocol feature, or
introduce a new transport protocol, protocol feature, or application application might require changes to such tools, and so could impact
might require changes to such tools, and so could impact operational operational practice and policies. Such changes have associated
practice and policies. Such changes have associated costs that are costs that are incurred by the network operators that need to update
incurred by the network operators that need to update their tooling their tooling or develop alternative practises that work without
or develop alternative practises that work without access to the access to the changed/removed information.
changed/removed information.
The use of encryption has the desirable effect of preventing The use of encryption has the desirable effect of preventing
unintended observation of the payload data and these tools seldom unintended observation of the payload data and these tools seldom
seek to observe the payload, or other application details. A flow seek to observe the payload, or other application details. A flow
that hides its transport header information could imply "don't touch" that hides its transport header information could imply "don't touch"
to some operators. This might limit a trouble-shooting response to to some operators. This might limit a trouble-shooting response to
"can't help, no trouble found". "can't help, no trouble found".
An alternative that does not require access to observable transport An alternative that does not require access to observable transport
headers is to access endpoint diagnostic tools or to include user headers is to access endpoint diagnostic tools or to include user
skipping to change at page 17, line 34 skipping to change at page 18, line 37
and the associated costs can be small. Equally, more extensive and the associated costs can be small. Equally, more extensive
changes to the transport tend to require more extensive, and more changes to the transport tend to require more extensive, and more
expensive, changes to tooling and operational practice. Protocol expensive, changes to tooling and operational practice. Protocol
designers can mitigate these costs by explicitly choosing to expose designers can mitigate these costs by explicitly choosing to expose
selected information as invariants that are guaranteed not to change selected information as invariants that are guaranteed not to change
for a particular protocol (e.g., the header invariants and the spin- for a particular protocol (e.g., the header invariants and the spin-
bit in QUIC [I-D.ietf-quic-transport]). Specification of common log bit in QUIC [I-D.ietf-quic-transport]). Specification of common log
formats and development of alternative approaches can also help formats and development of alternative approaches can also help
mitigate the costs of transport changes. mitigate the costs of transport changes.
2.4. To Support Header Compression 2.5. To Mitigate the Effects of Constrained Networks
Some link and network segments are constrained by the capacity they
can offer, by the time it takes to access capacity (e.g., due to
under-lying radio resource management methods), or by asymmetries in
the design (e.g., many link are designed so that the capacity
available is different in the forward and return directions; some
radio technologies have different access methods in the forward and
return directions resulting from differences in the power budget).
The impact of path constraints can be mitigated using a proxy
operating at or above the transport layer to use an alternate
transport protocol.
In many cases, one or both endpoints are unaware of the
characteristics of the constraining link or network segment and
mitigations are applied below the transport layer: Packet
classification and QoS methods (described in various sections) can be
beneficial in differentially prioritising certain traffic when there
is a capacity constraint or additional delay in scheduling link
transmissions. Another common mitigation is to apply header
compression over the specific link or subnetwork (see Section 2.5.1).
2.5.1. To Provide Header Compression
Header compression saves link capacity by compressing network and Header compression saves link capacity by compressing network and
transport protocol headers on a per-hop basis. This has been widely transport protocol headers on a per-hop basis. This has been widely
used with low bandwidth dial-up access links, and still finds used with low bandwidth dial-up access links, and still finds
application on wireless links that are subject to capacity application on wireless links that are subject to capacity
constraints. These methods are effective for bit-congestive links constraints. These methods are effective for bit-congestive links
sending small packets (e.g., reducing the cost for sending control sending small packets (e.g., reducing the cost for sending control
packets or small data packets over radio links). packets or small data packets over radio links).
Examples of header compression include use with TCP/IP and RTP/UDP/IP Examples of header compression include use with TCP/IP and RTP/UDP/IP
flows [RFC2507], [RFC6846], [RFC2508], [RFC5795]. Successful flows [RFC2507], [RFC6846], [RFC2508], [RFC5795], [RFC8724].
compression depends on observing the transport headers and Successful compression depends on observing the transport headers and
understanding of the way fields change between packets, and is hence understanding of the way fields change between packets, and is hence
incompatible with header encryption. Devices that compress transport incompatible with header encryption. Devices that compress transport
headers are dependent on a stable header format, implying headers are dependent on a stable header format, implying
ossification of that format. ossification of that format.
Introducing a new transport protocol, or changing the format of the Introducing a new transport protocol, or changing the format of the
transport header information, will limit the effectiveness of header transport header information, will limit the effectiveness of header
compression until the network devices are updated. Encrypting the compression until the network devices are updated. Encrypting the
transport protocol headers will tend to cause the header compression transport protocol headers will tend to cause the header compression
to a fall back to compressing only the network layer headers, with a to fall back to compressing only the network layer headers, with a
significant reduction in efficiency. This can limit connectivity if significant reduction in efficiency. This can limit connectivity if
the resulting flow exceeds the link capacity, or if the packets are the resulting flow exceeds the link capacity, or if the packets are
dropped because they exceed the link MTU. dropped because they exceed the link MTU.
The Secure RTP (SRTP) extensions [RFC3711] were explicitly designed The Secure RTP (SRTP) extensions [RFC3711] were explicitly designed
to leave the transport protocol headers unencrypted, but to leave the transport protocol headers unencrypted, but
authenticated, since support for header compression was considered authenticated, since support for header compression was considered
important. important.
2.5. To Verify SLA Compliance 2.6. To Verify SLA Compliance
Observable transport headers coupled with published transport Observable transport headers coupled with published transport
specifications allow operators and regulators to explore and verify specifications allow operators and regulators to explore and verify
compliance with Service Level Agreements (SLAs). It can also be used compliance with Service Level Agreements (SLAs). It can also be used
to understand whether a service is providing differential treatment to understand whether a service is providing differential treatment
to certain flows. to certain flows.
When transport header information cannot be observed, other methods When transport header information cannot be observed, other methods
have to be found to confirm that the traffic produced conforms to the have to be found to confirm that the traffic produced conforms to the
expectations of the operator or developer. expectations of the operator or developer.
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Independently verifiable performance metrics can be utilised to Independently verifiable performance metrics can be utilised to
demonstrate regulatory compliance in some jurisdictions, and as a demonstrate regulatory compliance in some jurisdictions, and as a
basis for informing design decisions. This can bring assurance to basis for informing design decisions. This can bring assurance to
those operating networks, often avoiding deployment of complex those operating networks, often avoiding deployment of complex
techniques that routinely monitor and manage Internet traffic flows techniques that routinely monitor and manage Internet traffic flows
(e.g., avoiding the capital and operational costs of deploying flow (e.g., avoiding the capital and operational costs of deploying flow
rate-limiting and network circuit-breaker methods [RFC8084]). rate-limiting and network circuit-breaker methods [RFC8084]).
3. Research, Development and Deployment 3. Research, Development and Deployment
Independently observed data is important to ensure the health of the Research and development of new protocols and mechanisms need to be
research and development communities and provides data need to informed by measurement data (as described in the previous section).
evaluate new proposals for standardisation. Data can also help Data can also help promote acceptance of proposed standards
promote acceptance of proposed specifications by the wider community specifications by the wider community (e.g., as a method to judge the
(e.g., as a method to judge the safety for Internet deployment). safety for Internet deployment).
Open standards motivate a desire to include independent observation
and evaluation of performance data, which in turn demands control/ Observed data is important to ensure the health of the research and
understanding about where and when measurement samples are collected. development communities, and provides data needed to evaluate new
This requires consideration of the methods used to observe proposals for standardisation. Open standards motivate a desire to
information and the appropriate balance between encrypting all and no include independent observation and evaluation of performance and
transport header information. deployment data. Independent data helps compare different methods,
judge the level of deployment and ensure the wider applicability of
the results. This is important when considering when a protocol or
mechanism should be standardised for use in the general Internet.
This, in turn, demands control/understanding about where and when
measurement samples are collected. This requires consideration of
the methods used to observe information and the appropriate balance
between encrypting all and no transport header information.
There can be performance and operational trade-offs in exposing There can be performance and operational trade-offs in exposing
selected information to network tools. This section explores key selected information to network tools. This section explores key
implications of tool and procedures that observe transport protocols, implications of tools and procedures that observe transport
but does not endorse or condemn any specific practices. protocols, but does not endorse or condemn any specific practises.
3.1. Independent Measurement 3.1. Independent Measurement
Encrypting transport header information has implications on the way Encrypting transport header information has implications on the way
network data is collected and analysed. Independent observation by network data is collected and analysed. Independent observation by
multiple actors is currently used by the transport community to multiple actors is currently used by the transport community to
maintain an accurate understanding of the network. When providing or maintain an accurate understanding of the network within transport
using such information, it is important to consider the privacy of area working groups, IRTF research groups, and the broader research
the user and their incentive for providing accurate and detailed community. This is important to be able to provide accountability,
information. and demonstrate that protocols behave as intended, although when
providing or using such information, it is important to consider the
privacy of the user and their incentive for providing accurate and
detailed information.
Protocols that expose the state of the transport protocol in their Protocols that expose the state of the transport protocol in their
header (e.g., timestamps used to calculate the RTT, packet numbers header (e.g., timestamps used to calculate the RTT, packet numbers
used to assess congestion and requests for retransmission) provide an used to assess congestion and requests for retransmission) provide an
incentive for a sending endpoint to provide consistent information, incentive for a sending endpoint to provide consistent information,
because a protocol will not work otherwise. An in-network observer because a protocol will not work otherwise. An on-path observer can
can have confidence that well-known (and ossified) transport header have confidence that well-known (and ossified) transport header
information represents the actual state of the endpoints, when this information represents the actual state of the endpoints, when this
information is necessary for the protocol's correct operation. information is necessary for the protocol's correct operation.
Encryption of transport header information could reduce the range of Encryption of transport header information could reduce the range of
actors that can observe useful data. This would limit the actors that can observe useful data. This would limit the
information sources available to the Internet community to understand information sources available to the Internet community to understand
the operation of new transport protocols, reducing information to the operation of new transport protocols, reducing information to
inform design decisions and standardisation of the new protocols and inform design decisions and standardisation of the new protocols and
related operational practises. The cooperating dependence of related operational practises. The cooperating dependence of
network, application, and host to provide communication performance network, application, and host to provide communication performance
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devices and within service platforms) can observe performance, and devices and within service platforms) can observe performance, and
when performance cannot be independently verified by all parties. when performance cannot be independently verified by all parties.
3.2. Measurable Transport Protocols 3.2. Measurable Transport Protocols
Transport protocol evolution, and the ability to measure and Transport protocol evolution, and the ability to measure and
understand the impact of protocol changes, have to proceed hand-in- understand the impact of protocol changes, have to proceed hand-in-
hand. A transport protocol that provides observable headers can be hand. A transport protocol that provides observable headers can be
used to provide open and verifiable measurement data. Observation of used to provide open and verifiable measurement data. Observation of
pathologies has a critical role in the design of transport protocol pathologies has a critical role in the design of transport protocol
mechanisms and development of new mechanisms and protocols. This mechanisms and development of new mechanisms and protocols, and aides
helps understand the interactions between cooperating protocols and understanding of the interactions between cooperating protocols and
network mechanisms, the implications of sharing capacity with other network mechanisms, the implications of sharing capacity with other
traffic and the impact of different patterns of usage. The ability traffic and the impact of different patterns of usage. The ability
of other stakeholders to review transport header traces helps develop of other stakeholders to review transport header traces helps develop
insight into performance and traffic contribution of specific insight into the performance and the traffic contribution of specific
variants of a protocol. variants of a protocol.
Development of new transport protocol mechanisms has to consider the Development of new transport protocol mechanisms has to consider the
scale of deployment and the range of environments in which the scale of deployment and the range of environments in which the
transport is used. Experience has shown that it is often difficult transport is used. Experience has shown that it is often difficult
to correctly implement new mechanisms [RFC8085], and that mechanisms to correctly implement new mechanisms [RFC8085], and that mechanisms
often evolve as a protocol matures, or in response to changes in often evolve as a protocol matures, or in response to changes in
network conditions, changes in network traffic, or changes to network conditions, changes in network traffic, or changes to
application usage. Analysis is especially valuable when based on the application usage. Analysis is especially valuable when based on the
behaviour experienced across a range of topologies, vendor equipment, behaviour experienced across a range of topologies, vendor equipment,
and traffic patterns. and traffic patterns.
Encryption enables a transport protocol to choose which internal Encryption enables a transport protocol to choose which internal
state to reveal to the network, what information to encrypt, and what state to reveal to devices on the network path, what information to
fields to grease [RFC8701]. A new design can provide summary encrypt, and what fields to grease [RFC8701]. A new design can
information regarding its performance, congestion control state, provide summary information regarding its performance, congestion
etc., or to make available explicit measurement information. For control state, etc., or to make available explicit measurement
example, [I-D.ietf-quic-transport] specifies a way for a QUIC information. For example, [I-D.ietf-quic-transport] specifies a way
endpoint to optionally set the spin-bit to reflect to explicitly for a QUIC endpoint to optionally set the spin-bit to explicitly
reveal the RTT of an encrypted transport session to the on-path reveal the RTT of an encrypted transport session to the on-path
network devices. There is a choice of what information to expose. network devices. There is a choice of what information to expose.
For some operational uses, the information has to contain sufficient For some operational uses, the information has to contain sufficient
detail to understand, and possibly reconstruct, the network traffic detail to understand, and possibly reconstruct, the network traffic
pattern for further testing. The interpretation of the information pattern for further testing. The interpretation of the information
needs to consider whether this information reflects the actual needs to consider whether this information reflects the actual
transport state of the endpoints. This might require the trust of transport state of the endpoints. This might require the trust of
transport protocol implementers, to correctly reveal the desired transport protocol implementers, to correctly reveal the desired
information. information.
New transport protocol formats are expected to facilitate an New transport protocol formats are expected to facilitate an
increased pace of transport evolution, and with it the possibility to increased pace of transport evolution, and with it the possibility to
experiment with and deploy a wide range of protocol mechanisms. At experiment with and deploy a wide range of protocol mechanisms. At
the time of writing, there has been interest in a wide range of new the time of writing, there has been interest in a wide range of new
transport methods, e.g., Larger Initial Window, Proportional Rate transport methods, e.g., Larger Initial Window, Proportional Rate
Reduction (PRR), congestion control methods based on measuring Reduction (PRR), congestion control methods based on measuring
bottleneck bandwidth and round-trip propagation time, the bottleneck bandwidth and round-trip propagation time, the
introduction of AQM techniques and new forms of ECN response (e.g., introduction of AQM techniques and new forms of ECN response (e.g.,
Data Centre TCP, DCTP, and methods proposed for L4S). The growth and Data Centre TCP, DCTCP, and methods proposed for L4S). The growth
diversity of applications and protocols using the Internet also and diversity of applications and protocols using the Internet also
continues to expand. For each new method or application, it is continues to expand. For each new method or application, it is
desirable to build a body of data reflecting its behaviour under a desirable to build a body of data reflecting its behaviour under a
wide range of deployment scenarios, traffic load, and interactions wide range of deployment scenarios, traffic load, and interactions
with other deployed/candidate methods. with other deployed/candidate methods.
3.3. Other Sources of Information 3.3. Other Sources of Information
Some measurements that traditionally rely on observable transport Some measurements that traditionally rely on observable transport
information could be completed by utilising endpoint-based logging information could be completed by utilising endpoint-based logging
(e.g., based on Quic-Trace [Quic-Trace]). Such information has a (e.g., based on Quic-Trace [Quic-Trace] and qlog
diversity of uses, including developers wishing to debug/understand [I-D.marx-qlog-main-schema]). Such information has a diversity of
the transport/application protocols with which they work, researchers uses, including developers wishing to debug/understand the transport/
seeking to spot trends and anomalies, and to characterise variants of application protocols with which they work, researchers seeking to
protocols. A standard format for endpoint logging could allow these spot trends and anomalies, and to characterise variants of protocols.
to be shared (after appropriate anonymisation) to understand A standard format for endpoint logging could allow these to be shared
performance and pathologies. (after appropriate anonymisation) to understand performance and
pathologies.
When measurement datasets are made available by servers or client When measurement datasets are made available by servers or client
endpoints, additional metadata, such as the state of the network and endpoints, additional metadata, such as the state of the network and
conditions in which the system was observed, is often necessary to conditions in which the system was observed, is often necessary to
interpret this data to answer questions about network performance or interpret this data to answer questions about network performance or
understand a pathology. Collecting and coordinating such metadata is understand a pathology. Collecting and coordinating such metadata is
more difficult when the observation point is at a different location more difficult when the observation point is at a different location
to the bottleneck or device under evaluation [RFC7799]. to the bottleneck or device under evaluation [RFC7799].
Despite being applicable in some scenarios, endpoint logs do not Despite being applicable in some scenarios, endpoint logs do not
provide equivalent information to in-network measurements. In provide equivalent information to on-path measurements made by
particular, endpoint logs contain only a part of the information to devices in the network. In particular, endpoint logs contain only a
understand the operation of network devices and identify issues such part of the information to understand the operation of network
as link performance or capacity sharing between multiple flows. An devices and identify issues such as link performance or capacity
analysis can require coordination between actors at different layers sharing between multiple flows. An analysis can require coordination
to successfully characterise flows and correlate the performance or between actors at different layers to successfully characterise flows
behaviour of a specific mechanism with an equipment configuration and and correlate the performance or behaviour of a specific mechanism
traffic using operational equipment along a network path (e.g., with an equipment configuration and traffic using operational
combining transport and network measurements to explore congestion equipment along a network path (e.g., combining transport and network
control dynamics, to understand the implications of traffic on measurements to explore congestion control dynamics, to understand
designs for active queue management or circuit breakers). the implications of traffic on designs for active queue management or
circuit breakers).
Another source of information could arise from operations, Another source of information could arise from operations,
administration and management (OAM) (see Section 6) information data administration and management (OAM) (see Section 6) information data
records [I-D.ietf-ippm-ioam-data] that could be embedded into header records could be embedded into header information at different layers
information at different layers to support functions such as to support functions such as performance evaluation, path-tracing,
performance evaluation, path-tracing, path verification information, path verification information, classification and a diversity of
classification and a diversity of other uses. other uses.
In-situ OAM (IOAM) data fields [I-D.ietf-ippm-ioam-data] can be
encapsulated into a variety of protocols to record operational and
telemetry information in an existing packet, while that packet
traverses a part of the path between two points in a network (e.g.,
within a particular IOAM management domain). The IOAM-Data-Fields
are independent from the protocols into which the IOAM-Data-Fields
are encapsulated. For example, IOAM can provide proof that a certain
traffic flow takes a pre-defined path, SLA verification for the live
data traffic, and statistics relating to traffic distribution.
4. Encryption and Authentication of Transport Headers 4. Encryption and Authentication of Transport Headers
There are several motivations for transport header encryption. There are several motivations for transport header encryption.
One motive to encrypt transport headers is to prevent network One motive to encrypt transport headers is to prevent network
ossification from network devices that inspect well-known transport ossification from network devices that inspect well-known transport
headers. Once a network device observes a transport header and headers. Once a network device observes a transport header and
becomes reliant upon using it, the overall use of that field can becomes reliant upon using it, the overall use of that field can
become ossified, preventing new versions of the protocol and become ossified, preventing new versions of the protocol and
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the presence of certain header fields exposed in TLS 1.2 the presence of certain header fields exposed in TLS 1.2
[RFC5426]. [RFC5426].
o The design of Multipath TCP (MPTCP) [RFC8684] had to account for o The design of Multipath TCP (MPTCP) [RFC8684] had to account for
middleboxes (known as "TCP Normalizers") that monitor the middleboxes (known as "TCP Normalizers") that monitor the
evolution of the window advertised in the TCP header and then evolution of the window advertised in the TCP header and then
reset connections when the window did not grow as expected. reset connections when the window did not grow as expected.
o TCP Fast Open [RFC7413] can experience problems due to middleboxes o TCP Fast Open [RFC7413] can experience problems due to middleboxes
that modify the transport header of packets by removing "unknown" that modify the transport header of packets by removing "unknown"
TCP options, segments with unrecognised TCP options can be TCP options. Segments with unrecognised TCP options can be
dropped, segments that contain data and set the SYN bit can be dropped, segments that contain data and set the SYN bit can be
dropped, or middleboxes that disrupt connections that send data dropped, and some middleboxes that disrupt connections that send
before completion of the three-way handshake. data before completion of the three-way handshake.
o Other examples of TCP ossification have included middleboxes that o Other examples of TCP ossification have included middleboxes that
modify transport headers by rewriting TCP sequence and modify transport headers by rewriting TCP sequence and
acknowledgement numbers, but are unaware of the (newer) TCP acknowledgement numbers, but are unaware of the (newer) TCP
selective acknowledgement (SACK) option and therefore fail to selective acknowledgement (SACK) option and therefore fail to
correctly rewrite the SACK information to match the changes made correctly rewrite the SACK information to match the changes made
to the fixed TCP header, preventing correct SACK operation. to the fixed TCP header, preventing correct SACK operation.
In all these cases, middleboxes with a hard-coded, but incomplete, In all these cases, middleboxes with a hard-coded, but incomplete,
understanding of a specific transport behaviour (i.e., TCP), understanding of a specific transport behaviour (i.e., TCP),
interacted poorly with transport protocols after the transport interacted poorly with transport protocols after the transport
behaviour was changed. In some case, the middleboxes modified or behaviour was changed. In some cases, the middleboxes modified or
replaced information in the transport protocol header. replaced information in the transport protocol header.
Transport header encryption prevents an on-path device from observing Transport header encryption prevents an on-path device from observing
the transport headers, and therefore stops ossified mechanisms being the transport headers, and therefore stops ossified mechanisms being
used that directly rely on or infer semantics of the transport header used that directly rely on or infer semantics of the transport header
information. This encryption is normally combined with information. This encryption is normally combined with
authentication of the protected information. RFC 8546 summarises authentication of the protected information. RFC 8546 summarises
this approach, stating that it is "The wire image, not the protocol's this approach, stating that it is "The wire image, not the protocol's
specification, determines how third parties on the network paths specification, determines how third parties on the network paths
among protocol participants will interact with that protocol" among protocol participants will interact with that protocol"
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Whatever the reasons, the IETF is designing protocols that include Whatever the reasons, the IETF is designing protocols that include
transport header encryption (e.g., QUIC [I-D.ietf-quic-transport]) to transport header encryption (e.g., QUIC [I-D.ietf-quic-transport]) to
supplement the already widespread payload encryption, and to further supplement the already widespread payload encryption, and to further
limit exposure of transport metadata to the network. limit exposure of transport metadata to the network.
If a transport protocol uses header encryption, the designers have to If a transport protocol uses header encryption, the designers have to
decide whether to encrypt all, or a part of, the transport layer decide whether to encrypt all, or a part of, the transport layer
information. Section 4 of [RFC8558] states: "Anything exposed to the information. Section 4 of [RFC8558] states: "Anything exposed to the
path should be done with the intent that it be used by the network path should be done with the intent that it be used by the network
elements on the path". Certain transport header fields can be made elements on the path".
observable in the network, or can define new fields designed to
explicitly expose observable transport layer information to the Certain transport header fields can be made observable to on-path
network. Where exposed fields are intended to be immutable (i.e., network devices, or can define new fields designed to explicitly
can be observed, but not modified by a network device), the endpoints expose observable transport layer information to the network. Where
are encouraged to use authentication to provide a cryptographic exposed fields are intended to be immutable (i.e., can be observed,
integrity check that can detect if these immutable fields have been but not modified by a network device), the endpoints are encouraged
modified by network devices. Authentication can help to prevent to use authentication to provide a cryptographic integrity check that
attacks that rely on sending packets that fake exposed control can detect if these immutable fields have been modified by network
signals in transport headers (e.g., TCP RST spoofing). Making a part devices. Authentication can help to prevent attacks that rely on
of a transport header observable or exposing new header fields can sending packets that fake exposed control signals in transport
lead to ossification of that part of a header as network devices come headers (e.g., TCP RST spoofing). Making a part of a transport
to rely on observations of the exposed fields. header observable or exposing new header fields can lead to
ossification of that part of a header as network devices come to rely
on observations of the exposed fields.
The use of transport header authentication and encryption therefore The use of transport header authentication and encryption therefore
exposes a tussle between middlebox vendors, operators, applications exposes a tussle between middlebox vendors, operators, researchers,
developers and users: applications developers, and end-users:
o On the one hand, future Internet protocols that support transport o On the one hand, future Internet protocols that support transport
header encryption assist in the restoration of the end-to-end header encryption assist in the restoration of the end-to-end
nature of the Internet by returning complex processing to the nature of the Internet by returning complex processing to the
endpoints, since middleboxes cannot modify what they cannot see, endpoints. Since middleboxes cannot modify what they cannot see,
and can improve privacy by reducing leakage of transport metadata. the use of transport header encryption can improve application and
end-user privacy by reducing leakage of transport metadata to
operators that deploy middleboxes.
o On the other hand, encryption of transport layer information has o On the other hand, encryption of transport layer information has
implications for people who are responsible for operating implications for network operators and researchers seeking to
networks, and researchers and analysts seeking to understand the understand the dynamics of protocols and traffic patterns, since
dynamics of protocols and traffic patterns. it reduces the information that is available to them.
The following briefly reviews some security design options for The following briefly reviews some security design options for
transport protocols. A Survey of the Interaction between Security transport protocols. A Survey of the Interaction between Security
Protocols and Transport Services [RFC8922] provides more details Protocols and Transport Services [RFC8922] provides more details
concerning commonly used encryption methods at the transport layer. concerning commonly used encryption methods at the transport layer.
Security work typically employs a design technique that seeks to Security work typically employs a design technique that seeks to
expose only what is needed [RFC3552]. This approach provides expose only what is needed [RFC3552]. This approach provides
incentives to not reveal any information that is not necessary for incentives to not reveal any information that is not necessary for
the end-to-end communication. The IAB has provided guidelines for the end-to-end communication. The IETF has provided guidelines for
writing Security Considerations for IETF specifications [RFC3552]. writing Security Considerations for IETF specifications [RFC3552].
Endpoint design choices impacting privacy also need to be considered Endpoint design choices impacting privacy also need to be considered
as a part of the design process [RFC6973]. The IAB has provided as a part of the design process [RFC6973]. The IAB has provided
guidance for analyzing and documenting privacy considerations within guidance for analyzing and documenting privacy considerations within
IETF specifications [RFC6973]. IETF specifications [RFC6973].
Authenticating the Transport Protocol Header: Transport layer header Authenticating the Transport Protocol Header: Transport layer header
information can be authenticated. An integrity check that information can be authenticated. An example transport
protects the immutable transport header fields, but can still authentication mechanism is TCP-Authentication (TCP-AO) [RFC5925].
expose the transport header information in the clear, allows in- This TCP option authenticates the IP pseudo header, TCP header,
network devices to observe these fields. An integrity check is and TCP data. TCP-AO protects the transport layer, preventing
not able to prevent in-network modification, but can prevent a attacks from disabling the TCP connection itself and provides
receiving endpoint from accepting changes and avoid impact on the replay protection. Such authentication might interact with
transport protocol operation, including some types of attack. middleboxes, depending on their behaviour [RFC3234].
An example transport authentication mechanism is TCP-
Authentication (TCP-AO) [RFC5925]. This TCP option authenticates
the IP pseudo header, TCP header, and TCP data. TCP-AO protects
the transport layer, preventing attacks from disabling the TCP
connection itself and provides replay protection. Such
authentication might interact with middleboxes, depending on their
behaviour [RFC3234].
The IPsec Authentication Header (AH) [RFC4302] was designed to The IPsec Authentication Header (AH) [RFC4302] was designed to
work at the network layer and authenticate the IP payload. This work at the network layer and authenticate the IP payload. This
approach authenticates all transport headers, and verifies their approach authenticates all transport headers, and verifies their
integrity at the receiver, preventing in-network modification. integrity at the receiver, preventing modification by network
The IPsec Encapsulating Security Payload (ESP) [RFC4303] can also devices on the path. The IPsec Encapsulating Security Payload
provide authentication and integrity without confidentiality using (ESP) [RFC4303] can also provide authentication and integrity
the NULL encryption algorithm [RFC2410]. SRTP [RFC3711] is without confidentiality using the NULL encryption algorithm
another example of a transport protocol that allows header [RFC2410]. SRTP [RFC3711] is another example of a transport
authentication. protocol that allows header authentication.
Integrity Check Transport protocols usually employ integrity checks
on the transport header information. Security method usually
employ stronger checks and can combine this with authentication.
An integrity check that protects the immutable transport header
fields, but can still expose the transport header information in
the clear, allows on-path network devices to observe these fields.
An integrity check is not able to prevent modification by network
devices on the path, but can prevent a receiving endpoint from
accepting changes and avoid impact on the transport protocol
operation, including some types of attack.
Selectively Encrypting Transport Headers and Payload: A transport Selectively Encrypting Transport Headers and Payload: A transport
protocol design that encrypts selected header fields, allows protocol design that encrypts selected header fields, allows
specific transport header fields to be made observable by network specific transport header fields to be made observable by network
devices. This information is explicitly exposed either in a devices on the path. This information is explicitly exposed
transport header field or lower layer protocol header. A design either in a transport header field or lower layer protocol header.
that only exposes immutable fields can also perform end-to-end A design that only exposes immutable fields can also perform end-
authentication of these fields across the path to prevent to-end authentication of these fields across the path to prevent
undetected modification of the immutable transport headers. undetected modification of the immutable transport headers.
Mutable fields in the transport header provide opportunities where Mutable fields in the transport header provide opportunities where
network devices can modify the transport behaviour (e.g., the on-path network devices can modify the transport behaviour (e.g.,
extended headers described in [I-D.trammell-plus-abstract-mech]). the extended headers described in
An example of a method that encrypts some, but not all, transport [I-D.trammell-plus-abstract-mech]). An example of a method that
header information is GRE-in-UDP [RFC8086] when used with GRE encrypts some, but not all, transport header information is GRE-
encryption. in-UDP [RFC8086] when used with GRE encryption.
Optional Encryption of Header Information: There are implications to Optional Encryption of Header Information: There are implications to
the use of optional header encryption in the design of a transport the use of optional header encryption in the design of a transport
protocol, where support of optional mechanisms can increase the protocol, where support of optional mechanisms can increase the
complexity of the protocol and its implementation, and in the complexity of the protocol and its implementation, and in the
management decisions that are have to be made to use variable management decisions that have to be made to use variable format
format fields. Instead, fields of a specific type ought to always fields. Instead, fields of a specific type ought to be sent with
be sent with the same level of confidentiality or integrity the same level of confidentiality or integrity protection.
protection.
Greasing: Protocols often provide extensibility features, reserving Greasing: Protocols often provide extensibility features, reserving
fields or values for use by future versions of a specification. fields or values for use by future versions of a specification.
The specification of receivers has traditionally ignored The specification of receivers has traditionally ignored
unspecified values, however in-network devices have emerged that unspecified values, however on-path network devices have emerged
ossify to require a certain value in a field, or re-use a field that ossify to require a certain value in a field, or re-use a
for another purpose. When the specification is later updated, it field for another purpose. When the specification is later
is impossible to deploy the new use of the field, and forwarding updated, it is impossible to deploy the new use of the field, and
of the protocol could even become conditional on a specific header forwarding of the protocol could even become conditional on a
field value. specific header field value.
A protocol can intentionally vary the value, format, and/or A protocol can intentionally vary the value, format, and/or
presence of observable transport header fields [RFC8701]. This presence of observable transport header fields at random
prevents a network device ossifying the use of a specific [RFC8701]. This prevents a network device ossifying the use of a
observable field and can ease future deployment of new uses of the specific observable field and can ease future deployment of new
value or codepoint. This is not a security mechanism, although uses of the value or code-point. This is not a security
the use can be combined with an authentication mechanism. mechanism, although the use can be combined with an authentication
mechanism.
Different transports use encryption to protect their header Different transports use encryption to protect their header
information to varying degrees. The trend is towards increased information to varying degrees. The trend is towards increased
protection. protection.
5. Intentionally Exposing Transport Information to the Network 5. Intentionally Exposing Transport Information to the Network
A transport protocol can choose to expose certain transport A transport protocol can choose to expose certain transport
information to on-path devices operating at the network layer by information to on-path devices operating at the network layer by
sending observable fields. One approach is to make an explicit sending observable fields. One approach is to make an explicit
choice not to encrypt certain transport header fields, making this choice not to encrypt certain transport header fields, making this
transport information observable by the network. Another approach is transport information observable by an on-path network device.
to expose transport information in a network-layer extension header Another approach is to expose transport information in a network-
(see Section 5.1). Both are examples of explicit information layer extension header (see Section 5.1). Both are examples of
intended to be used by network devices on the path [RFC8558]. explicit information intended to be used by network devices on the
path [RFC8558].
Whatever the mechanism used to expose the information, a decision to Whatever the mechanism used to expose the information, a decision to
expose only specific information, places the transport endpoint in expose only specific information places the transport endpoint in
control of what to expose outside of the encrypted transport header. control of what to expose outside of the encrypted transport header.
This decision can then be made independently of the transport This decision can then be made independently of the transport
protocol functionality. This can be done by exposing part of the protocol functionality. This can be done by exposing part of the
transport header or as a network layer option/extension. transport header or as a network layer option/extension.
5.1. Exposing Transport Information in Extension Headers 5.1. Exposing Transport Information in Extension Headers
At the network-layer, packets can carry optional headers that At the network-layer, packets can carry optional headers that
explicitly expose transport header information to the on-path devices explicitly expose transport header information to the on-path devices
operating at the network layer (Section 2.2.2). For example, an operating at the network layer (Section 2.3.2). For example, an
endpoint that sends an IPv6 Hop-by-Hop option [RFC8200] can provide endpoint that sends an IPv6 Hop-by-Hop option [RFC8200] can provide
explicit transport layer information that can be observed and used by explicit transport layer information that can be observed and used by
network devices on the path. New hop-by-hop options are not network devices on the path. New hop-by-hop options are not
recommended in RFC 8200 [RFC8200] "because nodes may be configured to recommended in RFC 8200 [RFC8200] "because nodes may be configured to
ignore the Hop-by-Hop Options header, drop packets containing a Hop- ignore the Hop-by-Hop Options header, drop packets containing a Hop-
by-Hop Options header, or assign packets containing a Hop-by-Hop by-Hop Options header, or assign packets containing a Hop-by-Hop
Options header to a slow processing path. Designers considering Options header to a slow processing path. Designers considering
defining new hop-by-hop options need to be aware of this likely defining new hop-by-hop options need to be aware of this likely
behavior." behavior."
Network-layer optional headers explicitly indicate the information Network-layer optional headers explicitly indicate the information
that is exposed, whereas use of exposed transport header information that is exposed, whereas use of exposed transport header information
first requires an observer to identify the transport protocol and its first requires an observer to identify the transport protocol and its
format. (See Section 2.1.) format. (See Section 2.2.)
An arbitrary path can include one or more network devices that drop An arbitrary path can include one or more network devices that drop
packets that include a specific header or option used for this packets that include a specific header or option used for this
purpose (see [RFC7872]). This could impact the proper functioning of purpose (see [RFC7872]). This could impact the proper functioning of
the protocols using the path. Protocol methods can be designed to the protocols using the path. Protocol methods can be designed to
probe to discover whether the specific option(s) can be used along probe to discover whether the specific option(s) can be used along
the current path, enabling use on arbitrary paths. the current path, enabling use on arbitrary paths.
5.2. Common Exposed Transport Information 5.2. Common Exposed Transport Information
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o On the one hand, explicitly exposing derived fields containing o On the one hand, explicitly exposing derived fields containing
relevant transport information (e.g., metrics for loss, latency, relevant transport information (e.g., metrics for loss, latency,
etc) can avoid network devices needing to derive this information etc) can avoid network devices needing to derive this information
from other header fields. This could result in development and from other header fields. This could result in development and
evolution of transport-independent tools around a common evolution of transport-independent tools around a common
observable header, and permit transport protocols to also evolve observable header, and permit transport protocols to also evolve
independently of this ossified header [RFC8558]. independently of this ossified header [RFC8558].
o On the other hand, protocols and implementations might be designed o On the other hand, protocols and implementations might be designed
to avoid consistently exposing external information that reflects to avoid consistently exposing external information that
the actual internal information used by the protocol itself. An corresponds to the actual internal information used by the
endpoint/protocol could choose to expose transport header protocol itself. An endpoint/protocol could choose to expose
information to optimise the benefit it gets from the network transport header information to optimise the benefit it gets from
[RFC8558]. The value of this information would be enhanced if the the network [RFC8558]. The value of this information for
exposed information could be verified to match the protocol's analysing operation of the transport layer would be enhanced if
observed behavior. the exposed information could be verified to match the transport
protocol's observed behavior.
The motivation to reflect actual transport header information and the The motivation to include actual transport header information and the
implications of network devices using this information has to be implications of network devices using this information has to be
considered when proposing such a method. RFC 8558 summarises this as considered when proposing such a method. RFC 8558 summarises this as
"When signals from endpoints to the path are independent from the "When signals from endpoints to the path are independent from the
signals used by endpoints to manage the flow's state mechanics, they signals used by endpoints to manage the flow's state mechanics, they
may be falsified by an endpoint without affecting the peer's may be falsified by an endpoint without affecting the peer's
understanding of the flow's state. For encrypted flows, this understanding of the flow's state. For encrypted flows, this
divergence is not detectable by on-path devices." [RFC8558]. divergence is not detectable by on-path devices [RFC8558].
6. Addition of Transport OAM Information to Network-Layer Headers 6. Addition of Transport OAM Information to Network-Layer Headers
If the transport headers are encrypted, on-path devices can make Even when the transport headers are encrypted, on-path devices can
measurements by utilising additional protocol headers carrying make measurements by utilising additional protocol headers carrying
operations, administration and management (OAM) information in an OAM information in an additional packet header. OAM information can
additional packet header. Using network-layer approaches to reveal be included with packets to perform functions such as identification
information has the potential that the same method (and hence same of transport protocols and flows, to aide understanding of network or
observation and analysis tools) can be consistently used by multiple transport performance, or to support network operations or mitigate
transport protocols. This approach also could be applied to methods the effects of specific network segments.
beyond OAM (see Section 5). There can also be less desirable
implications from separating the operation of the transport protocol Using network-layer approaches to reveal information has the
from the measurement framework. potential that the same method (and hence same observation and
analysis tools) can be consistently used by multiple transport
protocols. This approach also could be applied to methods beyond OAM
(see Section 5). There can also be less desirable implications from
separating the operation of the transport protocol from the
measurement framework.
6.1. Use of OAM within a Maintenance Domain 6.1. Use of OAM within a Maintenance Domain
OAM information can be added at the ingress to a maintenance domain OAM information can be restricted to a maintenance domain, typically
(e.g., an Ethernet protocol header with timestamps and sequence owned and operated by a single entity. OAM information can be added
number information using a method such as 802.11ag or in-situ OAM at the ingress to the maintenance domain (e.g., an Ethernet protocol
[I-D.ietf-ippm-ioam-data], or as a part of encapsulation protocol). header with timestamps and sequence number information using a method
This additional header information is not delivered to the endpoints such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data], or as a
and is typically removed at the egress of the maintenance domain. part of the encapsulation protocol). This additional header
information is not delivered to the endpoints and is typically
removed at the egress of the maintenance domain.
Although some types of measurements are supported, this approach does Although some types of measurements are supported, this approach does
not cover the entire range of measurements described in this not cover the entire range of measurements described in this
document. In some cases, it can be difficult to position measurement document. In some cases, it can be difficult to position measurement
tools at the appropriate segments/nodes and there can be challenges tools at the appropriate segments/nodes and there can be challenges
in correlating the downstream/upstream information when in-band OAM in correlating the downstream/upstream information when in-band OAM
data is inserted by an on-path device. data is inserted by an on-path device.
6.2. Use of OAM across Multiple Maintenance Domains 6.2. Use of OAM across Multiple Maintenance Domains
OAM information can also be added at the network layer by the sender OAM information can also be added at the network layer by the sender
as an IPv6 extension header or an IPv4 option, or in an as an IPv6 extension header or an IPv4 option, or in an
encapsulation/tunnel header that also includes an extension header or encapsulation/tunnel header that also includes an extension header or
option. This information can be used across multiple network option. This information can be used across multiple network
segments, or between the transport endpoints. segments, or between the transport endpoints.
One example is the IPv6 Performance and Diagnostic Metrics (PDM) One example is the IPv6 Performance and Diagnostic Metrics (PDM)
destination option [RFC8250]. This allows a sender to optionally destination option [RFC8250]. This allows a sender to optionally
include a destination option that caries header fields that can be include a destination option that carries header fields that can be
used to observe timestamps and packet sequence numbers. This used to observe timestamps and packet sequence numbers. This
information could be authenticated by a receiving transport endpoint information could be authenticated by a receiving transport endpoint
when the information is added at the sender and visible at the when the information is added at the sender and visible at the
receiving endpoint, although methods to do this have not currently receiving endpoint, although methods to do this have not currently
been proposed. This need to be explicitly enabled at the sender. been proposed. This needs to be explicitly enabled at the sender.
7. Conclusions 7. Conclusions
Header encryption and strong integrity checks are being incorporated Header encryption and strong integrity checks are being incorporated
into new transport protocols and have important benefits. The pace into new transport protocols and have important benefits. The pace
of development of transports using the WebRTC data channel, and the of development of transports using the WebRTC data channel, and the
rapid deployment of the QUIC transport protocol, can both be rapid deployment of the QUIC transport protocol, can both be
attributed to using the combination of UDP as a substrate while attributed to using the combination of UDP as a substrate while
providing confidentiality and authentication of the encapsulated providing confidentiality and authentication of the encapsulated
transport headers and payload. transport headers and payload.
This document has described some current practises, and the This document has described some current practises, and the
implications for some stakeholders, when transport layer header implications for some stakeholders, when transport layer header
encryption is used. It does not judge whether these practises are encryption is used. It does not judge whether these practises are
necessary, or endorse the use of any specific practise. Rather, the necessary, or endorse the use of any specific practise. Rather, the
intent is to highlight operational tools and practises to consider intent is to highlight operational tools and practises to consider
when designing and modifying transport protocols, so protocol when designing and modifying transport protocols, so protocol
designers can make informed choice about what transport header fields designers can make informed choices about what transport header
to encrypt, and whether it might be beneficial to make an explicit fields to encrypt, and whether it might be beneficial to make an
choice to expose certain fields to the network. In making such a explicit choice to expose certain fields to devices on the network
decision, it is important to balance: path. In making such a decision, it is important to balance:
o User Privacy: The less transport header information that is o User Privacy: The less transport header information that is
exposed to the network, the lower the risk of leaking metadata exposed to the network, the lower the risk of leaking metadata
that might have user privacy implications. Transports that chose that might have user privacy implications. Transports that chose
to expose some header fields need to make a privacy assessment to to expose some header fields need to make a privacy assessment to
understand the privacy cost versus benefit trade-off in making understand the privacy cost versus benefit trade-off in making
that information available. The design of the QUIC spin bit to that information available. The design of the QUIC spin bit to
the network is an example considered such analysis. the network is an example of such considered analysis.
o Transport Ossification: Unencrypted transport header fields are o Transport Ossification: Unencrypted transport header fields are
likely to ossify rapidly, as network devices come to rely on their likely to ossify rapidly, as network devices come to rely on their
presence, making it difficult to change the transport in future. presence, making it difficult to change the transport in future.
This argues that the choice to expose information to the network This argues that the choice to expose information to the network
is made deliberately and with care, since it is essentially is made deliberately and with care, since it is essentially
defining a stable interface between the transport and the network. defining a stable interface between the transport and the network.
Some protocols will want to make that interface as limited as Some protocols will want to make that interface as limited as
possible; other protocols might find value in exposing certain possible; other protocols might find value in exposing certain
information to signal to the network, or in allowing the network information to signal to the network, or in allowing the network
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available from unencrypted transport headers. The IETF has available from unencrypted transport headers. The IETF has
supported this practice by developing operations and management supported this practice by developing operations and management
specifications, interface specifications, and associated Best specifications, interface specifications, and associated Best
Current Practises. Widespread deployment of transport protocols Current Practises. Widespread deployment of transport protocols
that encrypt their information will impact network operations, that encrypt their information will impact network operations,
unless operators can develop alternative practises that work unless operators can develop alternative practises that work
without access to the transport header. without access to the transport header.
o Pace of Evolution: Removing obstacles to change can enable an o Pace of Evolution: Removing obstacles to change can enable an
increased pace of evolution. If a protocol changes its transport increased pace of evolution. If a protocol changes its transport
header format (wire image) or their transport behaviour, this can header format (wire image), or its transport behaviour, this can
result in the currently deployed tools and methods becoming no result in the currently deployed tools and methods becoming no
longer relevant. Where this needs to be accompanied by longer relevant. Where this needs to be accompanied by
development of appropriate operational support functions and development of appropriate operational support functions and
procedures, it can incur a cost in new tooling to catch-up with procedures, it can incur a cost in new tooling to catch-up with
each change. Protocols that consistently expose observable data each change. Protocols that consistently expose observable data
do not require such development, but can suffer from ossification do not require such development, but can suffer from ossification
and need to consider if the exposed protocol metadata has privacy and need to consider if the exposed protocol metadata has privacy
implications. There is no single deployment context, and implications. There is no single deployment context, and
therefore designers need to consider the diversity of operational therefore designers need to consider the diversity of operational
networks (ISPs, enterprises, Distributed DoS (DDoS) mitigation and networks (ISPs, enterprises, DDoS mitigation and firewall
firewall maintainers, etc.). maintainers, etc.).
o Supporting Common Specifications: Common, open, specifications can o Supporting Common Specifications: Common, open, transport
stimulate engagement by developers, users, researchers, and the specifications can stimulate engagement by developers, users,
broader community. Increased protocol diversity can be beneficial researchers, and the broader community. Increased protocol
in meeting new requirements, but the ability to innovate without diversity can be beneficial in meeting new requirements, but the
public scrutiny risks point solutions that optimise for specific ability to innovate without public scrutiny risks point solutions
cases, but that can accidentally disrupt operations of/in that optimise for specific cases, and that can accidentally
different parts of the network. The social contract that disrupt operations of/in different parts of the network. The
maintains the stability of the Internet relies on accepting common social contract that maintains the stability of the Internet
interworking specifications, and on it being possible to detect relies on accepting common transport specifications, and on it
violations. It is important to find new ways of maintaining that being possible to detect violations. The existence of independent
community trust as increased use of transport header encryption measurements, transparency, and public scrutiny of transport
limits visibility into transport behaviour. protocol behaviour, help the community to enforce the social norm
that protocol implementations behave fairly and conform (at least
mostly) to the specifications. It is important to find new ways
of maintaining that community trust as increased use of transport
header encryption limits visibility into transport behaviour (see
also Section 5.3).
o Impact on Benchmarking and Understanding Feature Interactions: An o Impact on Benchmarking and Understanding Feature Interactions: An
appropriate vantage point for observation, coupled with timing appropriate vantage point for observation, coupled with timing
information about traffic flows, provides a valuable tool for information about traffic flows, provides a valuable tool for
benchmarking network devices, endpoint stacks, and/or benchmarking network devices, endpoint stacks, and/or
configurations. This can help understand complex feature configurations. This can help understand complex feature
interactions. An inability to observe transport header interactions. An inability to observe transport header
information can make it harder to diagnose and explore information can make it harder to diagnose and explore
interactions between features at different protocol layers, a interactions between features at different protocol layers, a
side-effect of not allowing a choice of vantage point from which side-effect of not allowing a choice of vantage point from which
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what can be observed. This document does not make recommendations what can be observed. This document does not make recommendations
about what information ought to be exposed, to whom it ought to be about what information ought to be exposed, to whom it ought to be
observable, or how this will be achieved. There are also design observable, or how this will be achieved. There are also design
choices about where observable fields are placed. For example, one choices about where observable fields are placed. For example, one
location could be a part of the transport header outside of the location could be a part of the transport header outside of the
encryption envelope, another alternative is to carry the information encryption envelope, another alternative is to carry the information
in a network-layer option or extension header. New transport in a network-layer option or extension header. New transport
protocol designs ought to explicitly identify any fields that are protocol designs ought to explicitly identify any fields that are
intended to be observed, consider if there are alternative ways of intended to be observed, consider if there are alternative ways of
providing the information, and reflect on the implications of providing the information, and reflect on the implications of
observable fields being used by network devices, and how this might observable fields being used by on-path network devices, and how this
impact user privacy and protocol evolution when these fields become might impact user privacy and protocol evolution when these fields
ossified. become ossified.
As [RFC7258] notes, "Making networks unmanageable to mitigate As [RFC7258] notes, "Making networks unmanageable to mitigate
(pervasive monitoring) is not an acceptable outcome, but ignoring (pervasive monitoring) is not an acceptable outcome, but ignoring
(pervasive monitoring) would go against the consensus documented (pervasive monitoring) would go against the consensus documented
here." Providing explicit information can help avoid traffic being here." Providing explicit information can help avoid traffic being
inappropriately classified, impacting application performance. An inappropriately classified, impacting application performance. An
appropriate balance will emerge over time as real instances of this appropriate balance will emerge over time as real instances of this
tension are analysed [RFC7258]. This balance between information tension are analysed [RFC7258]. This balance between information
exposed and information hidden ought to be carefully considered when exposed and information hidden ought to be carefully considered when
specifying new transport protocols. specifying new transport protocols.
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throughout this document. throughout this document.
Authentication, confidentiality protection, and integrity protection Authentication, confidentiality protection, and integrity protection
are identified as Transport Features by [RFC8095]. As currently are identified as Transport Features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a deployed in the Internet, these features are generally provided by a
protocol or layer on top of the transport protocol [RFC8922]. protocol or layer on top of the transport protocol [RFC8922].
Confidentiality and strong integrity checks have properties that can Confidentiality and strong integrity checks have properties that can
also be incorporated into the design of a transport protocol or to also be incorporated into the design of a transport protocol or to
modify an existing transport. Integrity checks can protect an modify an existing transport. Integrity checks can protect an
endpoint from undetected modification of protocol fields by network endpoint from undetected modification of protocol fields by on-path
devices, whereas encryption and obfuscation or greasing can further network devices, whereas encryption and obfuscation or greasing can
prevent these headers being utilised by network devices [RFC8701]. further prevent these headers being utilised by network devices
Preventing observation of headers provides an opportunity for greater [RFC8701]. Preventing observation of headers provides an opportunity
freedom to update the protocols and can ease experimentation with new for greater freedom to update the protocols and can ease
techniques and their final deployment in endpoints. A protocol experimentation with new techniques and their final deployment in
specification needs to weigh the costs of ossifying common headers, endpoints. A protocol specification needs to weigh the costs of
versus the potential benefits of exposing specific information that ossifying common headers, versus the potential benefits of exposing
could be observed along the network path to provide tools to manage specific information that could be observed along the network path to
new variants of protocols. provide tools to manage new variants of protocols.
Header encryption can provide confidentiality of some or all of the Header encryption can provide confidentiality of some or all of the
transport header information. This prevents an on-path device from transport header information. This prevents an on-path device from
knowledge of the header field. It therefore prevents mechanisms gaining knowledge of the header field. It therefore prevents
being built that directly rely on the information or seeks to infer mechanisms being built that directly rely on the information or seeks
semantics of an exposed header field. Reduced visibility into to infer semantics of an exposed header field. Reduced visibility
transport metadata can limit the ability to measure and characterise into transport metadata can limit the ability to measure and
traffic, and conversely can provide privacy benefits. characterise traffic, and conversely can provide privacy benefits.
Extending the transport payload security context to also include the Extending the transport payload security context to also include the
transport protocol header protects both information with the same transport protocol header protects both types of information with the
key. A privacy concern would arise if this key was shared with a same key. A privacy concern would arise if this key was shared with
third party, e.g., providing access to transport header information a third party, e.g., providing access to transport header information
to debug a performance issue, would also result in exposing the to debug a performance issue, would also result in exposing the
transport payload data to the same third party. Such risks would be transport payload data to the same third party. Such risks would be
mitigated using a layered security design that provides one domain of mitigated using a layered security design that provides one domain of
protection and associated keys for the transport payload and protection and associated keys for the transport payload and
encrypted transport headers; and a separate domain of protection and encrypted transport headers; and a separate domain of protection and
associated keys for any observable transport header fields. associated keys for any observable transport header fields.
Exposed transport headers are sometimes utilised as a part of the Exposed transport headers are sometimes utilised as a part of the
information to detect anomalies in network traffic. "While PM is an information to detect anomalies in network traffic. "While PM is an
attack, other forms of monitoring that might fit the definition of PM attack, other forms of monitoring that might fit the definition of PM
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packet). These techniques are currently used by some operators to packet). These techniques are currently used by some operators to
also defend from distributed DoS attacks. also defend from distributed DoS attacks.
Exposed transport header fields can also form a part of the Exposed transport header fields can also form a part of the
information used by the receiver of a transport protocol to protect information used by the receiver of a transport protocol to protect
the transport layer from data injection by an attacker. In the transport layer from data injection by an attacker. In
evaluating this use of exposed header information, it is important to evaluating this use of exposed header information, it is important to
consider whether it introduces a significant DoS threat. For consider whether it introduces a significant DoS threat. For
example, an attacker could construct a DoS attack by sending packets example, an attacker could construct a DoS attack by sending packets
with a sequence number that falls within the currently accepted range with a sequence number that falls within the currently accepted range
of sequence numbers at the receiving endpoint, this would then of sequence numbers at the receiving endpoint. This would then
introduce additional work at the receiving endpoint, even though the introduce additional work at the receiving endpoint, even though the
data in the attacking packet might not finally be delivered by the data in the attacking packet might not finally be delivered by the
transport layer. This is sometimes known as a "shadowing attack". transport layer. This is sometimes known as a "shadowing attack".
An attack can, for example, disrupt receiver processing, trigger loss An attack can, for example, disrupt receiver processing, trigger loss
and retransmission, or make a receiving endpoint perform unproductive and retransmission, or make a receiving endpoint perform unproductive
decryption of packets that cannot be successfully decrypted (forcing decryption of packets that cannot be successfully decrypted (forcing
a receiver to commit decryption resources, or to update and then a receiver to commit decryption resources, or to update and then
restore protocol state). restore protocol state).
One mitigation to off-path attack is to deny knowledge of what header One mitigation to off-path attack is to deny knowledge of what header
skipping to change at page 33, line 38 skipping to change at page 36, line 5
[RFC6056], or a port value that cannot be predicted (see Section 5.1 [RFC6056], or a port value that cannot be predicted (see Section 5.1
of [RFC8085]). A receiver could also require additional information of [RFC8085]). A receiver could also require additional information
to be used as a part of a validation check before accepting packets to be used as a part of a validation check before accepting packets
at the transport layer (e.g., utilising a part of the sequence number at the transport layer (e.g., utilising a part of the sequence number
space that is encrypted; or by verifying an encrypted token not space that is encrypted; or by verifying an encrypted token not
visible to an attacker). This would also mitigate against on-path visible to an attacker). This would also mitigate against on-path
attacks. An additional processing cost can be incurred when attacks. An additional processing cost can be incurred when
decryption is attempted before a receiver discards an injected decryption is attempted before a receiver discards an injected
packet. packet.
Open standards motivate a desire for this evaluation to include The existence of open transport protocol standards, and a research
independent observation and evaluation of performance data, which in and operations community with a history of independent observation
turn suggests control over where and when measurement samples are and evaluation of performance data, encourages fairness and
collected. This requires consideration of the appropriate balance conformance to those standards. This suggests careful consideration
between encrypting all and no transport header information. Open will be made over where, and when, measurement samples are collected.
data, and accessibility to tools that can help understand trends in An appropriate balance between encrypting some or all of the
application deployment, network traffic and usage patterns can all transport header information needs to be considered. Open data, and
contribute to understanding security challenges. accessibility to tools that can help understand trends in application
deployment, network traffic and usage patterns can all contribute to
understanding security challenges.
The Security and Privacy Considerations in the Framework for Large- The Security and Privacy Considerations in the Framework for Large-
Scale Measurement of Broadband Performance (LMAP) [RFC7594] contain Scale Measurement of Broadband Performance (LMAP) [RFC7594] contain
considerations for Active and Passive measurement techniques and considerations for Active and Passive measurement techniques and
supporting material on measurement context. supporting material on measurement context.
Addition of observable transport information to the path increases Addition of observable transport information to the path increases
the information available to an observer and may, when this the information available to an observer and may, when this
information can be linked to a node or user, reduce the privacy of information can be linked to a node or user, reduce the privacy of
the user. See the security considerations of [RFC8558]. the user. See the security considerations of [RFC8558].
skipping to change at page 34, line 39 skipping to change at page 37, line 10
This work has received funding from the UK Engineering and Physical This work has received funding from the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1. Sciences Research Council under grant EP/R04144X/1.
11. Informative References 11. Informative References
[bufferbloat] [bufferbloat]
Gettys, J. and K. Nichols, "Bufferbloat: dark buffers in Gettys, J. and K. Nichols, "Bufferbloat: dark buffers in
the Internet. Communications of the ACM, 55(1):57-65", the Internet. Communications of the ACM, 55(1):57-65",
January 2012. January 2012.
[I-D.ietf-6man-ipv6-alt-mark]
Fioccola, G., Zhou, T., Cociglio, M., and F. Qin, "IPv6
Application of the Alternate Marking Method", draft-ietf-
6man-ipv6-alt-mark-00 (work in progress), May 2020.
[I-D.ietf-ippm-ioam-data] [I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", draft-ietf-ippm-ioam-data-10 (work in for In-situ OAM", draft-ietf-ippm-ioam-data-10 (work in
progress), July 2020. progress), July 2020.
[I-D.ietf-quic-transport] [I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-29 (work and Secure Transport", draft-ietf-quic-transport-29 (work
in progress), June 2020. in progress), June 2020.
[I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-19
(work in progress), November 2017.
[I-D.ietf-tls-dtls13] [I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-38 (work in progress), May 1.3", draft-ietf-tls-dtls13-38 (work in progress), May
2020. 2020.
[I-D.ietf-tsvwg-rtcweb-qos] [I-D.ietf-tsvwg-rtcweb-qos]
Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP
Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb- Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb-
qos-18 (work in progress), August 2016. qos-18 (work in progress), August 2016.
[I-D.marx-qlog-main-schema]
Marx, R., "Main logging schema for qlog", draft-marx-qlog-
main-schema-02 (work in progress), November 2020.
[I-D.trammell-plus-abstract-mech] [I-D.trammell-plus-abstract-mech]
Trammell, B., "Abstract Mechanisms for a Cooperative Path Trammell, B., "Abstract Mechanisms for a Cooperative Path
Layer under Endpoint Control", draft-trammell-plus- Layer under Endpoint Control", draft-trammell-plus-
abstract-mech-00 (work in progress), September 2016. abstract-mech-00 (work in progress), September 2016.
[Latency] Briscoe, B., "Reducing Internet Latency: A Survey of [Latency] Briscoe, B., "Reducing Internet Latency: A Survey of
Techniques and Their Merits, IEEE Comm. Surveys & Techniques and Their Merits, IEEE Comm. Surveys &
Tutorials. 26;18(3) p2149-2196", November 2014. Tutorials. 26;18(3) p2149-2196", November 2014.
[Measurement] [Measurement]
skipping to change at page 37, line 33 skipping to change at page 40, line 5
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006, DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/info/rfc4585>. <https://www.rfc-editor.org/info/rfc4585>.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, [RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737, S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
DOI 10.17487/RFC4737, November 2006, DOI 10.17487/RFC4737, November 2006,
<https://www.rfc-editor.org/info/rfc4737>. <https://www.rfc-editor.org/info/rfc4737>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC5166] Floyd, S., Ed., "Metrics for the Evaluation of Congestion
Control Mechanisms", RFC 5166, DOI 10.17487/RFC5166, March
2008, <https://www.rfc-editor.org/info/rfc5166>.
[RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful [RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful
Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008, Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,
<https://www.rfc-editor.org/info/rfc5218>. <https://www.rfc-editor.org/info/rfc5218>.
[RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A., and R. [RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A., and R.
Whitner, "Improved Packet Reordering Metrics", RFC 5236, Whitner, "Improved Packet Reordering Metrics", RFC 5236,
DOI 10.17487/RFC5236, June 2008, DOI 10.17487/RFC5236, June 2008,
<https://www.rfc-editor.org/info/rfc5236>. <https://www.rfc-editor.org/info/rfc5236>.
[RFC5426] Okmianski, A., "Transmission of Syslog Messages over UDP", [RFC5426] Okmianski, A., "Transmission of Syslog Messages over UDP",
skipping to change at page 39, line 5 skipping to change at page 41, line 30
"RObust Header Compression (ROHC): A Profile for TCP/IP "RObust Header Compression (ROHC): A Profile for TCP/IP
(ROHC-TCP)", RFC 6846, DOI 10.17487/RFC6846, January 2013, (ROHC-TCP)", RFC 6846, DOI 10.17487/RFC6846, January 2013,
<https://www.rfc-editor.org/info/rfc6846>. <https://www.rfc-editor.org/info/rfc6846>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013, DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>. <https://www.rfc-editor.org/info/rfc6973>.
[RFC7098] Carpenter, B., Jiang, S., and W. Tarreau, "Using the IPv6
Flow Label for Load Balancing in Server Farms", RFC 7098,
DOI 10.17487/RFC7098, January 2014,
<https://www.rfc-editor.org/info/rfc7098>.
[RFC7126] Gont, F., Atkinson, R., and C. Pignataro, "Recommendations [RFC7126] Gont, F., Atkinson, R., and C. Pignataro, "Recommendations
on Filtering of IPv4 Packets Containing IPv4 Options", on Filtering of IPv4 Packets Containing IPv4 Options",
BCP 186, RFC 7126, DOI 10.17487/RFC7126, February 2014, BCP 186, RFC 7126, DOI 10.17487/RFC7126, February 2014,
<https://www.rfc-editor.org/info/rfc7126>. <https://www.rfc-editor.org/info/rfc7126>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>. 2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[RFC7414] Duke, M., Braden, R., Eddy, W., Blanton, E., and A.
Zimmermann, "A Roadmap for Transmission Control Protocol
(TCP) Specification Documents", RFC 7414,
DOI 10.17487/RFC7414, February 2015,
<https://www.rfc-editor.org/info/rfc7414>.
[RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF [RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF
Recommendations Regarding Active Queue Management", Recommendations Regarding Active Queue Management",
BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015, BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,
<https://www.rfc-editor.org/info/rfc7567>. <https://www.rfc-editor.org/info/rfc7567>.
[RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T., [RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A Framework for Large-Scale Aitken, P., and A. Akhter, "A Framework for Large-Scale
Measurement of Broadband Performance (LMAP)", RFC 7594, Measurement of Broadband Performance (LMAP)", RFC 7594,
DOI 10.17487/RFC7594, September 2015, DOI 10.17487/RFC7594, September 2015,
<https://www.rfc-editor.org/info/rfc7594>. <https://www.rfc-editor.org/info/rfc7594>.
skipping to change at page 42, line 15 skipping to change at page 44, line 43
[RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C. [RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <https://www.rfc-editor.org/info/rfc8684>. 2020, <https://www.rfc-editor.org/info/rfc8684>.
[RFC8701] Benjamin, D., "Applying Generate Random Extensions And [RFC8701] Benjamin, D., "Applying Generate Random Extensions And
Sustain Extensibility (GREASE) to TLS Extensibility", Sustain Extensibility (GREASE) to TLS Extensibility",
RFC 8701, DOI 10.17487/RFC8701, January 2020, RFC 8701, DOI 10.17487/RFC8701, January 2020,
<https://www.rfc-editor.org/info/rfc8701>. <https://www.rfc-editor.org/info/rfc8701>.
[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>.
[RFC8837] Jones, P., Dhesikan, S., Jennings, C., and D. Druta,
"Differentiated Services Code Point (DSCP) Packet Markings
for WebRTC QoS", RFC 8837, DOI 10.17487/RFC8837, January
2021, <https://www.rfc-editor.org/info/rfc8837>.
[RFC8922] Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C. [RFC8922] Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C.
Wood, "A Survey of the Interaction between Security Wood, "A Survey of the Interaction between Security
Protocols and Transport Services", RFC 8922, Protocols and Transport Services", RFC 8922,
DOI 10.17487/RFC8922, October 2020, DOI 10.17487/RFC8922, October 2020,
<https://www.rfc-editor.org/info/rfc8922>. <https://www.rfc-editor.org/info/rfc8922>.
Appendix A. Revision information Appendix A. Revision information
-00 This is an individual draft for the IETF community. -00 This is an individual draft for the IETF community.
skipping to change at page 46, line 36 skipping to change at page 49, line 36
comments. comments.
OPSEC:: No additional changes were requested in the OPSEC review. OPSEC:: No additional changes were requested in the OPSEC review.
IETF LC:: Tom Herbert: Please refer to 8200 on EH :: addressed in IETF LC:: Tom Herbert: Please refer to 8200 on EH :: addressed in
response to Joel above. Michael Richardson, Fernando Gont, Tom response to Joel above. Michael Richardson, Fernando Gont, Tom
Herbert: Continuation of discussion on domains where EH might be (or Herbert: Continuation of discussion on domains where EH might be (or
not) useful and the tussle on what information to reveal. Unclear not) useful and the tussle on what information to reveal. Unclear
yet what additional text should be changed within this ID. yet what additional text should be changed within this ID.
Authors' Addresses ------------
- 21 Revised after IESG review:
Revision 21 includes revised text after comments from Zahed, Erik
Kline, Rob Wilton, Eric Vyncke, Roman Danyliw, and Benjamin Kaduk.
Authors' Addresses
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Department of Engineering Department of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen AB24 3UE Aberdeen AB24 3UE
Scotland Scotland
EMail: gorry@erg.abdn.ac.uk EMail: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/ URI: http://www.erg.abdn.ac.uk/
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
School of Computing Science School of Computing Science
Glasgow G12 8QQ Glasgow G12 8QQ
Scotland Scotland
EMail: csp@csperkins.org EMail: csp@csperkins.org
URI: https://csperkins.org/ URI: https://csperkins.org/
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