draft-ietf-tsvwg-transport-encrypt-03.txt   draft-ietf-tsvwg-transport-encrypt-04.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: May 29, 2019 University of Glasgow Expires: August 22, 2019 University of Glasgow
November 25, 2018 February 18, 2019
The Impact of Transport Header Confidentiality on Network Operation and The Impact of Transport Header Confidentiality on Network Operation and
Evolution of the Internet Evolution of the Internet
draft-ietf-tsvwg-transport-encrypt-03 draft-ietf-tsvwg-transport-encrypt-04
Abstract Abstract
This document describes implications of applying end-to-end This document describes implications of applying end-to-end
encryption at the transport layer. It identifies in-network uses of encryption at the transport layer. It identifies in-network uses of
transport layer header information. It then reviews the implications transport layer header information. It then reviews the implications
of developing end-to-end transport protocols that use authentication of developing end-to-end transport protocols that use authentication
to protect the integrity of transport information or encryption to to protect the integrity of transport information or encryption to
provide confidentiality of the transport protocol header and expected provide confidentiality of the transport protocol header and expected
implications of transport protocol design and network operation. implications of transport protocol design and network operation.
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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 May 29, 2019. This Internet-Draft will expire on August 22, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 3 2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 3
3. Current uses of Transport Headers within the Network . . . . 10 3. Current uses of Transport Headers within the Network . . . . 10
3.1. Observing Transport Information in the Network . . . . . 10 3.1. Observing Transport Information in the Network . . . . . 10
3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 16 3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 16
3.3. Use for Network Diagnostics and Troubleshooting . . . . . 19 3.3. Use for Network Diagnostics and Troubleshooting . . . . . 20
3.4. Header Compression . . . . . . . . . . . . . . . . . . . 20 3.4. Header Compression . . . . . . . . . . . . . . . . . . . 21
4. Encryption and Authentication of Transport Headers . . . . . 21 4. Encryption and Authentication of Transport Headers . . . . . 21
5. Addition of Transport Information to Network-Layer Protocol 5. Addition of Transport Information to Network-Layer Protocol
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6. Implications of Protecting the Transport Headers . . . . . . 26 6. Implications of Protecting the Transport Headers . . . . . . 26
6.1. Independent Measurement . . . . . . . . . . . . . . . . . 26 6.1. Independent Measurement . . . . . . . . . . . . . . . . . 26
6.2. Characterising "Unknown" Network Traffic . . . . . . . . 27 6.2. Characterising "Unknown" Network Traffic . . . . . . . . 28
6.3. Accountability and Internet Transport Protocols . . . . . 27 6.3. Accountability and Internet Transport Protocols . . . . . 28
6.4. Impact on Research, Development and Deployment . . . . . 28 6.4. Impact on Operational Cost . . . . . . . . . . . . . . . 29
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.5. Impact on Research, Development and Deployment . . . . . 30
8. Security Considerations . . . . . . . . . . . . . . . . . . . 31 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 30
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 8. Security Considerations . . . . . . . . . . . . . . . . . . . 33
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
11. Informative References . . . . . . . . . . . . . . . . . . . 33 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35
Appendix A. Revision information . . . . . . . . . . . . . . . . 40 11. Informative References . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 Appendix A. Revision information . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction 1. Introduction
There is increased interest in, and deployment of, new protocols that There is increased interest in, and deployment of, new protocols that
employ end-to-end encryption at the transport layer, including the employ end-to-end encryption at the transport layer, including the
transport layer headers. An example of such a transport is the QUIC transport layer headers. An example of such a transport is the QUIC
transport protocol [I-D.ietf-quic-transport], currently being transport protocol [I-D.ietf-quic-transport], currently being
standardised in the IETF. Encryption of transport layer headers and standardised in the IETF. Encryption of transport layer headers and
payload data has many benefits in terms of protecting user privacy. payload data has many benefits in terms of protecting user privacy.
These benefits have been widely discussed [RFC7258], [RFC7624], and These benefits have been widely discussed [RFC7258], [RFC7624], and
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This document discusses some consequences of applying end-to-end This document discusses some consequences of applying end-to-end
encryption at the transport layer. It reviews the implications of encryption at the transport layer. It reviews the implications of
developing end-to-end transport protocols that use encryption to developing end-to-end transport protocols that use encryption to
provide confidentiality of the transport protocol header, and provide confidentiality of the transport protocol header, and
considers the effect of such changes on transport protocol design and considers the effect of such changes on transport protocol design and
network operations. It also considers anticipated implications on network operations. It also considers anticipated implications on
transport and application evolution. transport and application evolution.
Transports are increasingly encrypting and authenticating the payload Transports are increasingly encrypting and authenticating the payload
(i.e., the application data carried within the transport connection) (i.e., the application data carried within the transport connection)
end-to-end. Such protection is encouraged, and iits implications are end-to-end. Such protection is encouraged, and the implications are
not further discussed in this memo. not further discussed in this memo.
2. Context and Rationale 2. Context and Rationale
The transport layer provides end-to-end interactions between The transport layer provides end-to-end interactions between
endpoints (processes) using an Internet path. Transport protocols endpoints (processes) using an Internet path. Transport protocols
layer directly over the network-layer service and are sent in the layer directly over the network-layer service and are sent in the
payload of network-layer packets. They support end-to-end payload of network-layer packets. They support end-to-end
communication between applications, supported by higher-layer communication between applications, supported by higher-layer
protocols, running on the end systems (or transport endpoints). This protocols, running on the end systems (or transport endpoints). This
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selection of appropriate mechanisms, to ensure a safe, reliable, and selection of appropriate mechanisms, to ensure a safe, reliable, and
robust Internet (e.g., [RFC1273]). In turn, the network operations robust Internet (e.g., [RFC1273]). In turn, the network operations
community relies on being able to understand the pattern and community relies on being able to understand the pattern and
requirements of traffic passing over the Internet, both in aggregate requirements of traffic passing over the Internet, both in aggregate
and at the flow level. and at the flow level.
There are many motivations for deploying encrypted transports There are many motivations for deploying encrypted transports
[RFC7624] (i.e., transport protocols that use encryption to provide [RFC7624] (i.e., transport protocols that use encryption to provide
confidentiality of some or all of the transport-layer header confidentiality of some or all of the transport-layer header
information), and encryption of transport payloads (i.e. information), and encryption of transport payloads (i.e.
confidentiality of the payload data). The increasing public concerns Confidentiality of the payload data). The increasing public concerns
about interference with Internet traffic have led to a rapidly about interference with Internet traffic have led to a rapidly
expanding deployment of encryption to protect end-user privacy, e.g., expanding deployment of encryption to protect end-user privacy, e.g.,
QUIC [I-D.ietf-quic-transport]. Encryption is also expected to form QUIC [I-D.ietf-quic-transport]. Encryption is also expected to form
a basis of future transport protocol designs. a basis of future transport protocol designs.
Some network operators and access providers have come to rely on the Some network operators and access providers have come to rely on the
in-network measurement of transport properties and the functionality in-network measurement of transport properties and the functionality
provided by middleboxes to both support network operations and provided by middleboxes to both support network operations and
enhance performance. There can therefore be implications when enhance performance. There can therefore be implications when
working with encrypted transport protocols that hide transport header working with encrypted transport protocols that hide transport header
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some cases, this could be benign or advantageous to the protocol some cases, this could be benign or advantageous to the protocol
(e.g., recognising the start of a connection, or explicitly exposing (e.g., recognising the start of a connection, or explicitly exposing
protocol information can be expected to provide more consistent protocol information can be expected to provide more consistent
decisions by on-path devices than the use of diverse methods to infer decisions by on-path devices than the use of diverse methods to infer
semantics from other flow properties); in other cases this is not semantics from other flow properties); in other cases this is not
beneficial (e.g., a mechanism implemented in a network device, such beneficial (e.g., a mechanism implemented in a network device, such
as a firewall, that required a header field to have only a specific as a firewall, that required a header field to have only a specific
known set of values could prevent the device from forwarding packets known set of values could prevent the device from forwarding packets
using a different version of a protocol that introduces a new feature using a different version of a protocol that introduces a new feature
that changes the value present in this field, preventing evolution of that changes the value present in this field, preventing evolution of
the protocol). the protocol). Experience developing Transport Layer Security
[RFC8446], required a design that recognised that deployed
middleboxes relied on the exposed information in TLS 1.2
Examples of the impact of ossification on transport protocol design Examples of the impact of ossification on transport protocol design
and ease of deployment can be seen in the case of Multipath TCP and ease of deployment can be seen in the case of Multipath TCP
(MPTCP) and the TCP Fast Open option. The design of MPTCP had to be (MPTCP) and the TCP Fast Open option. The design of MPTCP had to be
revised to account for middleboxes, so called "TCP Normalizers", that revised to account for middleboxes, so called "TCP Normalizers", that
monitor the evolution of the window advertised in the TCP headers and monitor the evolution of the window advertised in the TCP headers and
that reset connections if the window does not grow as expected. that reset connections if the window does not grow as expected.
Similarly, TCP Fast Open has had issues with middleboxes that remove Similarly, TCP Fast Open has had issues with middleboxes that remove
unknown TCP options, that drop segments with unknown TCP options, unknown TCP options, that drop segments with unknown TCP options,
that drop segments that contain data and have the SYN bit set, that that drop segments that contain data and have the SYN bit set, that
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In both cases, the issue was caused by middleboxes that had a hard- In both cases, the issue was caused by middleboxes that had a hard-
coded understanding of transport behaviour, and that interacted coded understanding of transport behaviour, and that interacted
poorly with transports that tried to change that behaviour. Other poorly with transports that tried to change that behaviour. Other
examples have included middleboxes that rewrite TCP sequence and examples have included middleboxes that rewrite TCP sequence and
acknowledgement numbers but are unaware of the (newer) SACK option acknowledgement numbers but are unaware of the (newer) SACK option
and don't correctly rewrite selective acknowledgements to match the and don't correctly rewrite selective acknowledgements to match the
changes made to the fixed TCP header. changes made to the fixed TCP header.
A protocol design that uses header encryption can provide A protocol design that uses header encryption can provide
confidentiality of some or all of the protocol header information. confidentiality of some or all of the protocol header information.
This prevents an on-path device from gaining knowledge of the header Encryption with secure key distribution prevents an on-path device
field. It therefore prevents mechanisms being built that directly from observing the header field. It therefore prevents mechanisms
rely on the information or seek to infer semantics of an exposed being built that directly rely on the information or seek to infer
header field. Using encryption to provide confidentiality of the semantics of an exposed header field. Using encryption to provide
transport layer brings some well-known privacy and security benefits confidentiality of the transport layer brings some well-known privacy
and can therefore help reduce ossification of the transport layer. and security benefits and can therefore help reduce ossification of
In particular, it is important that protocols either do not expose the transport layer. In particular, it is important that protocols
information where the usage could change in future protocols, or that either do not expose information where the usage could change in
methods that utilise the information are robust to potential changes future protocols, or that methods that utilise the information are
as protocols evolve over time. To avoid unwanted inspection, a robust to potential changes as protocols evolve over time. To avoid
protocol could also intentionally vary the format and/or value of unwanted inspection, a protocol could also intentionally vary the
header fields (sometimes known as Greasing format and/or value of header fields (sometimes known as Greasing
[I-D.thomson-quic-grease]). However, while encryption hides the [I-D.thomson-quic-grease]). However, while encryption hides the
protocol header information, it does not prevent ossification of the protocol header information, it does not prevent ossification of the
network service. People seeking understanding of network traffic network service. People seeking understanding of network traffic
could come to rely on pattern inferences and other heuristics as the could come to rely on pattern inferences and other heuristics as the
basis for network decision and to derive measurement data, creating basis for network decision and to derive measurement data, creating
new dependencies on the transport protocol. new dependencies on the transport protocol.
Specification of non-encrypted transport header fields explicitly Specification of non-encrypted transport header fields explicitly
allows protocol designers to make specific header information allows protocol designers to make specific header information
observable in the network. This supports other uses of this observable in the network. This supports other uses of this
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network forwarding could evolve to depend on the presence and/or network forwarding could evolve to depend on the presence and/or
value of these fields. The decision about which transport headers value of these fields. The decision about which transport headers
fields are made observable offers trade-offs around authentication fields are made observable offers trade-offs around authentication
and confidentiality versus observability, network operations and and confidentiality versus observability, network operations and
management, and ossification. For example, a design that provides management, and ossification. For example, a design that provides
confidentiality of protocol header information can impact the confidentiality of protocol header information can impact the
following activities that rely on measurement and analysis of traffic following activities that rely on measurement and analysis of traffic
flows: flows:
Network Operations and Research: Observable transport headers enable Network Operations and Research: Observable transport headers enable
both operators and the research community to measure and analyse both operators and the research community to explicitly measure
protocol performance, network anomalies, and failure pathologies. and analyse protocol performance, network anomalies, and failure
pathologies.
This information can help inform capacity planning, and assist in This information can help inform capacity planning, and assist in
determining the need for equipment and/or configuration changes by determining the need for equipment and/or configuration changes by
network operators. network operators.
The data can also inform Internet engineering research, and help The data can also inform Internet engineering research, and help
in the development of new protocols, methodologies, and in the development of new protocols, methodologies, and
procedures. Concealing the transport protocol header information procedures. Concealing the transport protocol header information
makes the stream performance unavailable to passive observers makes the stream performance unavailable to passive observers
along the path, and likely leads to the development of alternative along the path, and likely leads to the development of alternative
methods to collect or infer that data. methods to collect or infer that data (for example heuristics
based on analysis of traffic patterns).
Providing confidentiality of the transport payload, but leaving Providing confidentiality of the transport payload, but leaving
some, or all, of the transport headers unencrypted, possibly with some, or all, of the transport headers unencrypted, possibly with
authentication, can provide the majority of the privacy and authentication, can provide many of the privacy and security
security benefits while supporting operations and research, but at benefits while supporting operations and research, but at the cost
the cost of ossifying the transport headers. of ossifying the transport headers.
Protection from Denial of Service: Observable transport headers Protection from Denial of Service: Observable transport headers
currently provide useful input to classify traffic and detect currently provide useful input to classify traffic and detect
anomalous events (e.g., changes in application behaviour, anomalous events (e.g., changes in application behaviour,
distributed denial of service attacks). To be effective, this distributed denial of service attacks). To be effective, this
protection needs to be able to uniquely disambiguate unwanted protection needs to be able to uniquely disambiguate unwanted
traffic. An inability to separate this traffic using packet traffic. An inability to separate this traffic using packet
header information could result in less-efficient identification header information could result in less-efficient identification
of unwanted traffic or development of different methods (e.g. of unwanted traffic or development of different methods (e.g.
rate-limiting of uncharacterised traffic). rate-limiting of uncharacterised traffic).
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[RFC7983]. [RFC7983].
Flow identification is a common function. For example, performed by Flow identification is a common function. For example, performed by
measurement activities, QoS classification, firewalls, Denial of measurement activities, QoS classification, firewalls, Denial of
Service, DOS, prevention. It becomes more complex and less easily Service, DOS, prevention. It becomes more complex and less easily
achieved when multiplexing is used at or above the transport layer. achieved when multiplexing is used at or above the transport layer.
3.1.2. Metrics derived from Transport Layer Headers 3.1.2. Metrics derived from Transport Layer Headers
Some actors manage their portion of the Internet by characterizing Some actors manage their portion of the Internet by characterizing
the performance of link/network segments. Passive monitoring uses the performance of link/network segments. Passive monitoring can
observed traffic to make inferences from transport headers to derive observe traffic that does not encrypt the transport header
these performance metrics. A variety of open source and commercial information to make inferences from transport headers to derive these
tools have been deployed that utilise this information. The performance metrics. A variety of open source and commercial tools
following metrics can be derived from transport header information: have been deployed that utilise this information. The following
metrics can be derived from transport header information:
Traffic Rate and Volume: Header information (e.g., sequence number Traffic Rate and Volume: Header information (e.g., sequence number
and packet size) allows derivation of volume measures per- and packet size) allows derivation of volume measures per-
application, to characterise the traffic that uses a network application, to characterise the traffic that uses a network
segment or the pattern of network usage. This can be measured per segment or the pattern of network usage. This can be measured per
endpoint or for an aggregate of endpoints (e.g., by an operator to endpoint or for an aggregate of endpoints (e.g., by an operator to
assess subscriber usage). It can also be used to trigger assess subscriber usage). It can also be used to trigger
measurement-based traffic shaping and to implement QoS support measurement-based traffic shaping and to implement QoS support
within the network and lower layers. Volume measures can be within the network and lower layers. Volume measures can be
valuable for capacity planning and providing detail of trends, valuable for capacity planning and providing detail of trends,
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deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit 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
[RFC7567], current methods [RFC8290] [RFC8289] [RFC8033] often [RFC7567], current methods [RFC8290] [RFC8289] [RFC8033] often
cannot scale across all possible deployment scenarios. cannot scale across all possible deployment scenarios.
Variation in delay: Some network applications are sensitive to small Variation in delay: Some network applications are sensitive to small
changes in packet timing. To assess the performance of such changes in packet timing (jitter). Short and long-term delay
applications, it can be necessary to measure the variation in variation can impact on the latency of a flow and the hence the
delay observed along a portion of the path [RFC3393] [RFC5481]. perceived quality of applications using the network (e.g., jitter
The requirements resemble those for the measurement of latency. metrics are often cited when characterising paths supporting real-
time traffic). To assess the performance of such applications, it
can be necessary to measure the variation in delay observed along
a portion of the path [RFC3393] [RFC5481]. 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 impacted by reordering (e.g., triggering TCP retransmission, or
re-buffering of real-time applications). Packet reordering can re-buffering of real-time applications). Packet reordering can
occur for many reasons, from equipment design to misconfiguration occur for many reasons, from equipment design to misconfiguration
of forwarding rules. Since this impacts transport performance, of forwarding rules. Since this impacts transport performance,
network tools are needed to detect and measure unwanted/excessive network tools are needed to detect and measure unwanted/excessive
reordering. reordering.
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to enable a different forwarding treatment by the network, even when to enable a different forwarding treatment by the network, even when
a transport employs encryption to protect other header information. a 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 could wish to hide the presence and characteristics of sub-flows could wish to hide 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 network needs of individual sub-flows. There are and to reflect the network needs of individual sub-flows. There are
several ways this could be done: several ways this could be done:
Using the IPv6 Network-Layer Flow Label: Endpoints are encouraged to IP Address: Applications expose the addresses used by endpoints, and
set the IPv6 Flow Label field of the network-layer header (e.g., this is used in the forwarding decisions in network devices.
Address and other protocol information can be used by a Multi-
Field (MF) classifier to determine how traffic is treated
[RFC2475], and hence the quality of experience for a flow.
[RFC8085]). The label can provide information that can help Using the IPv6 Network-Layer Flow Label: A number of Standards Track
inform network-layer queuing, forwarding (e.g., for Equal Cost and Best Current Practice RFCs (e.g., [RFC8085], [RFC6437],
Multi-Path, ECMP, routing, and Link Aggregation, LAG) [RFC6294]. [RFC6438]) encourage endpoints to set the IPv6 Flow label field of
A multiplexing transport could choose to use multiple flow labels the network-layer header. IPv6 "source nodes SHOULD assign each
to allow the network to independently forward subflows. unrelated transport connection and application data stream to a
new flow" [RFC6437]. A multiplexing transport could choose to use
multiple Flow labels to allow the network to independently forward
subflows. RFC6437 provides further guidance on choosing a flow
label value, stating these "should be chosen such that their bits
exhibit a high degree of variability", and chosen so that "third
parties should be unlikely to be able to guess the next value that
a source of flow labels will choose". To promote privacy, the
Flow Label assignment needs to avoid introducing linkability that
a network device may observe. Once set, a label can provide
information that can help inform network-layer queuing and
forwarding [RFC6438](e.g. for Equal Cost Multi-Path, ECMP,
routing, and Link Aggregation, LAG) [RFC6294]. [RFC6438] includes
describes considerations when used with IPsec.
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 the network
by setting the Differentiated Services Code Point (DSCP) field of by setting the Differentiated Services Code Point (DSCP) field of
IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications
identify different forwarding treatments for individual sub-flows identify different forwarding treatments for individual sub-flows
(audio vs. video) based on the value of the DSCP field (audio vs. video) based on the value of the DSCP field
[I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information [I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information
to inform network-layer queuing and forwarding, rather than an to inform network-layer queuing and forwarding, rather than an
operator inferring traffic requirements from transport and operator inferring traffic requirements from transport and
application headers via a multi-field classifier. application headers via a multi-field classifier.
Since the DSCP value can impact the quality of experience for a Since the DSCP value can impact the quality of experience for a
flow., observations of service performance need to consider this flow, observations of service performance need to consider this
field when a network path has support for differentiated service field when a network path has support for differentiated service
treatment. treatment.
Using Explicit Congestion Marking: ECN [RFC3168] is a transport Using Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that utilises the ECN field in the network-layer header. mechanism that utilises 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 flows packets. is ECN-capable, and requests ECN treatment of the flows packets.
An ECN-capable transport can offer benefits when used over a path An ECN-capable transport can offer benefits when used over a path
with equipment that implements an AQM method with Congestion with equipment that implements an AQM method with Congestion
Experienced (CE) marking of IP packets [RFC8087], since it can Experienced (CE) marking of IP packets [RFC8087], since it can
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make appropriate QoS decisions, or response to other queries about make appropriate QoS decisions, or response to other queries about
the network service. For some this will be blessing, for others it the network service. For some this will be blessing, for others it
may be a curse. For example, operational performance data about may be a curse. For example, operational performance data about
encrypted flows needs to be determined by traffic pattern analysis, encrypted flows needs to be determined by traffic pattern analysis,
rather than relying on traditional tools. This can impact the rather than relying on traditional tools. This can impact the
ability of the operator to respond to faults, it could require ability of the operator to respond to faults, it could require
reliance on endpoint diagnostic tools or user involvement in reliance on endpoint diagnostic tools or user involvement in
diagnosing and troubleshooting unusual use cases or non-trivial diagnosing and troubleshooting unusual use cases or non-trivial
problems. A key need here is for tools to provide useful information problems. A key need here is for tools to provide useful information
during network anomalies (e.g., significant reordering, high or during network anomalies (e.g., significant reordering, high or
intermittent loss). Many network operators currently utilise intermittent loss).
observed transport information as a part of their operational
practice. However, the network will not break just because transport
headers are encrypted, although alternative diagnostic and
troubleshooting tools would need to be developed and deployed.
Measurements can be used to monitor the health of a portion of the Measurements can be used to monitor the health of a portion of the
Internet, to provide early warning of the need to take action. They Internet, to provide early warning of the need to take action. They
can assist in debugging and diagnosing the root causes of faults that can assist in debugging and diagnosing the root causes of faults that
concern a particular user's traffic. They can also be used to concern a particular user's traffic. They can also be used to
support post-mortem investigation after an anomaly to determine the support post-mortem investigation after an anomaly to determine the
root cause of a problem. root cause of a problem.
In some case, measurements may involve active injection of test In some case, measurements may involve active injection of test
traffic to complete a measurement. However, most operators do not traffic to perform a measurement. However, most operators do not
have access to user equipment, and injection of test traffic may be have access to user equipment, therefore the point of test is
associated with costs in running such tests (e.g., the implications normally different from the transport endpoint. Injection of test
of capacity tests in a mobile network are obvious). Some active traffic can incur an additional costs in running such tests (e.g.,
measurements (e.g., response under load or particular workloads) the implications of capacity tests in a mobile network are obvious).
perturb other traffic, and could require dedicated access to the Some active measurements (e.g., response under load or particular
network segment. An alternative approach is to use in-network workloads) perturb other traffic, and could require dedicated access
techniques that observe transport packet headers in operational to the network segment. An alternative approach is to use in-network
networks to make the measurements. techniques that observe transport packet headers added while traffic
traverses an operational networks to make the measurements. These
measurements do not require the cooperation of an endpoint.
In other cases, measurement involves dissecting network traffic In other cases, measurement involves dissecting network traffic
flows. The observed transport layer information can help identify flows. The observed transport layer information can help identify
whether the link/network tuning is effective and alert to potential whether the link/network tuning is effective and alert to potential
problems that can be hard to derive from link or device measurements problems that can be hard to derive from link or device measurements
alone. The design trade-offs for radio networks are often very alone. The design trade-offs for radio networks are often very
different to those of wired networks. A radio-based network (e.g., different to those of wired networks. A radio-based network (e.g.,
cellular mobile, enterprise WiFi, satellite access/back-haul, point- cellular mobile, enterprise WiFi, satellite access/back-haul, point-
to-point radio) has the complexity of a subsystem that performs radio to-point radio) has the complexity of a subsystem that performs radio
resource management,s with direct impact on the available capacity, resource management,s with direct impact on the available capacity,
skipping to change at page 25, line 13 skipping to change at page 25, line 36
fields. Instead, fields of a specific type ought to always be fields. Instead, fields of a specific type ought to always be
sent with the same level of confidentiality or integrity sent with the same level of confidentiality or integrity
protection. protection.
As seen, different transports use encryption to protect their header As seen, different transports use encryption to protect their header
information to varying degrees. There is, however, a trend towards information to varying degrees. There is, however, a trend towards
increased protection with newer transport protocols. increased protection with newer transport protocols.
5. Addition of Transport Information to Network-Layer Protocol Headers 5. Addition of Transport Information to Network-Layer Protocol Headers
Transport protocol information can be made visible in a network-layer
header. This has the advantage that this information can then be
observed by in-network devices.
Information from the transport protocol can be used by a multi-field
classifier to prioritise flows as a part of a policy framework. This
was discussed in Section 3.1.3.
Some measurements can be made by adding additional protocol headers Some measurements can be made by adding additional protocol headers
carrying operations, administration and management (OAM) information carrying operations, administration and management (OAM) information
to packets at the ingress to a maintenance domain (e.g., an Ethernet to packets at the ingress to a maintenance domain (e.g., an Ethernet
protocol header with timestamps and sequence number information using protocol header with timestamps and sequence number information using
a method such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data]) a method such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data])
and removing the additional header at the egress of the maintenance and removing the additional header at the egress of the maintenance
domain. This approach enables some types of measurements, but does domain. This approach enables some types of measurements, but 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 required segments/nodes and there can be challenges in tools at the required segments/nodes and there can be challenges in
skipping to change at page 26, line 17 skipping to change at page 26, line 33
manipulate this header information to gain an advantage from the manipulate this header information to gain an advantage from the
network. network.
6. Implications of Protecting the Transport Headers 6. Implications of Protecting the Transport Headers
The choice of which fields to expose and which to encrypt is a design The choice of which fields to expose and which to encrypt is a design
choice for the transport protocol. Any selective encryption method choice for the transport protocol. Any selective encryption method
requires trading two conflicting goals for a transport protocol requires trading two conflicting goals for a transport protocol
designer to decide which header fields to encrypt. Security work designer to decide which header fields to encrypt. Security work
typically employs a design technique that seeks to expose only what typically employs a design technique that seeks to expose only what
is needed. However, there can be performance and operational is needed. This approach provides incentives to not reveal any
benefits in exposing selected information to network tools. information that is not necessary for the end-to-end communication.
However, there can be performance and operational benefits in
exposing selected information to network tools.
This section explores key implications of working with encrypted This section explores key implications of working with encrypted
transport protocols. transport protocols.
6.1. Independent Measurement 6.1. Independent Measurement
Independent observation by multiple actors is important for Independent observation by multiple actors is important for
scientific analysis. Encrypting transport header encryption changes scientific analysis. Encrypting transport header encryption changes
the ability for other actors to collect and independently analyse the ability for other actors to collect and independently analyse
data. Internet transport protocols employ a set of mechanisms. Some data. Internet transport protocols employ a set of mechanisms. Some
of these need to work in cooperation with the network layer - loss of these need to work in cooperation with the network layer - loss
detection and recovery, congestion detection and congestion control, detection and recovery, congestion detection and congestion control,
some of these need to work only end-to-end (e.g., parameter some of these need to work only end-to-end (e.g., parameter
negotiation, flow-control). negotiation, flow-control).
When encryption conceals information in the transport header, it The majority of present Internet applications use two well-known
could be possible for an applications to provide summary data on transport protocols, TCP and UDP. Although TCP represents the
performance and usage of the network. This data could be made majority of current traffic, some real-time applications use UDP, and
available to other actors. However, this data needs to contain much of this traffic utilises RTP format headers in the payload of
sufficient detail to understand (and possibly reconstruct the network the UDP datagram. Since these protocol headers have been fixed for
traffic pattern for further testing) and to be correlated with the decades, a range of tools and analysis methods have became common and
configuration of the network paths being measured. well-understood.
Sharing information between actors needs also to consider the privacy Protocols that expose the state information used by the transport
of the user and the incentives for providing accurate and detailed protocol in their header information (e.g., timestamps used to
information. Protocols that expose the state information used by the calculate the RTT, packet numbers used to asses congestion and
transport protocol in their header information (e.g., timestamps used
to calculate the RTT, packet numbers used to asses congestion and
requests for retransmission) provide an incentive for the sending requests for retransmission) provide an incentive for the sending
endpoint to provide correct information, increasing confidence that endpoint to provide correct information, increasing confidence that
the observer understands the transport interaction with the network. the observer understands the transport interaction with the network.
This can support decisions when considering changes to transport For example, when TCP is used over an unencrypted network path (i.e.,
protocols, changes in network infrastructure, or the emergence of new one that does not use IPsec or other encryption below the transport),
traffic patterns. it implicitly exposes header information that can be used for
measurement at any point along the path. This information is
necessary for the protocol's correct operation, therefore there is no
incentive for a TCP implementation to put incorrect information in
this transport header. A network device can have confidence that the
well-known (and ossified) transport information represents the actual
state of the endpoints.
When encryption is used to conceal some or all of the transport
headers, the transport protocol choose what information to reveal to
the network about its internal state, what information to leave
encrypted, and what fields to grease to protect against future
ossification. Such a transport could be designed, for example, to
provide summary data regarding its performance, congestion control
state, etc., or to make an explicit measurement signal available.
For example, a QUIC endpoint could set the spin bit to reflect to
explicitly reveal a session's RTT [I-D.ietf-quic-spin-exp]).
When providing or using such information, it becomes important to
consider the privacy of the user and their incentive for providing
accurate and detailed information. Protocols that selectively reveal
some transport state or measurement signals are choosing to establish
a trust relationship with the network operators. There is no
protocol mechanism that can guarantee that the information provided
represents the actual transport state of the endpoints, since those
endpoints can always send additional information in the encrypted
part of the header, to update to replace whatever they reveal. This
reduces the ability to independently measure and verify that a
protocol is behaving as expected. Some operational uses need the
information to contain sufficient detail to understand, and possibly
reconstruct, the network traffic pattern for further testing; such
operators must gain the trust of transport protocol implementers if
they are to correctly reveal such information.
For some usage a standardised endpoint-based logging format (e.g.,
based onQuic-Trace [Quic-Trace]) could offer an alternative to in-
network measurement. Such information will have a diversity of uses
- examples include developers wishing to debug/understand the
transport/applictaion protocols with which they work, to researchers
seeking to spot trends, anomalies and to characterise variants of
protocols. This use will need to establish the validity and
provenance of the logging information (e.g., to establish how and
when traces were captured).
However, endpoint logs do not provide equivalent information to in-
network measurements. In particular, endpoint logs contain only a
part of the information needed to understand the operation of network
devices and identify issues such as link performance or capacity
sharing between multiple flows. Additional information is needed to
determine which equipment/links are used and the configuration of
equipment along the network paths being measured.
6.2. Characterising "Unknown" Network Traffic 6.2. Characterising "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.
If "unknown" or "uncharacterised" traffic patterns form a small part If "unknown" or "uncharacterised" traffic patterns form a small part
of the traffic aggregate passing through a network device or segment of the traffic aggregate passing through a network device or segment
of the network the path, the dynamics of the uncharacterised traffic of the network the path, the dynamics of the uncharacterised traffic
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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. On a shorter timescale,
information may also need to be collected to manage denial of service information may also need to be collected to manage denial of service
attacks against the infrastructure. attacks against the infrastructure.
6.3. Accountability and Internet Transport Protocols 6.3. Accountability and Internet Transport Protocols
Information provided by tools observing transport headers can be used Information provided by tools observing transport headers can be used
to classify traffic, and to limit the network capacity used by to classify traffic, and to limit the network capacity used by
certain flows. Operators can potentially use this information to certain flows, as discussed in Section 3.2.4). Equally, operators
prioritise or de-prioritise certain flows or classes of flow, with
potential implications for network neutrality, or to rate limit
malicious or otherwise undesirable flows (e.g., for Distributed
Denial of Service, DDOS, protection, or to ensure compliance with a
traffic profile, as discussed in Section 3.2.4). Equally, operators
could use analysis of transport headers and transport flow state to could use analysis of transport headers and transport flow state to
demonstrate that they are not providing differential treatment to demonstrate that they are not providing differential treatment to
certain flows. Obfuscating or hiding this information using certain flows. Obfuscating or hiding this information using
encryption may lead operators and maintainers of middleboxes encryption may lead operators and maintainers of middleboxes
(firewalls, etc.) to seek other methods to classify, and potentially (firewalls, etc.) to seek other methods to classify, and potentially
other mechanisms to condition, network traffic. other mechanisms to condition, network traffic.
A lack of data reduces the level of precision with which flows can be A lack of data that reduces the level of precision with which flows
classified and conditioning mechanisms can be applied (e.g., rate can be classified also reduces the design space for conditioning
limiting, circuit breaker techniques [RFC8084], or blocking of mechanisms (e.g., rate limiting, circuit breaker techniques
uncharacterised traffic), and this needs to be considered when [RFC8084], or blocking of uncharacterised traffic), and this needs to
evaluating the impact of designs for transport encryption [RFC5218]. be considered when evaluating the impact of designs for transport
encryption [RFC5218].
6.4. Impact on Research, Development and Deployment 6.4. Impact on Operational Cost
The majority of present Internet applications use two well-known Many network operators currently utilise observed transport
transport protocols, TCP and UDP. Although TCP represents the information as a part of their operational practice, and have
majority of current traffic, some real-time applications use UDP, and developed tools and operational practices based around currently
much of this traffic utilises RTP format headers in the payload of deployed transports and their applications. Encryption of the
the UDP datagram. Since these protocol headers have been fixed for transport information prevents tools from directly observing this
decades, a range of tools and analysis methods have became common and information. A variety of open source and commercial tools have been
well-understood. Over this period, the transport protocol headers deployed that utilise this information for a variety of short and
have mostly changed slowly, and so also the need to develop tools long term measurements.
track new versions of the protocol.
Looking ahead, there will be a need to update these protocols and to The network will not break just because transport headers are
develop and deploy new transport mechanisms and protocols. There are encrypted, although alternative diagnostic and troubleshooting tools
both opportunities and also challenges to the design, evaluation and would need to be developed and deployed. Introducing a new protocol
deployment of new transport protocol mechanisms. or application can require these tool chains and practice to be
updated, and may in turn impact operational mechanisms, and policies.
Each change can introduce associated costs, including the cost of
collecting data, and the tooling needed to handle multiple formats
(possibly as these co-exist in the network, when measurements need to
span time periods during which changes are deployed, or to compare
with historical data). These costs are incurred by an operator to
manage the service and debug network issues.
Integrity checks can protect an endpoint from undetected modification At the time of writing, the additional operational cost of using
of protocol fields by network devices, whereas encryption and encrypted transports is not yet well understood. Design trade-offs
obfuscation can further prevent these headers from being utilised by could mitigate these costs by explicitly choosing to expose selected
network devices. Hiding headers can therefore provide the information (e.g., header invariants and the spin-bit in
opportunity for greater freedom to update the protocols, and can ease QUIC[I-D.ietf-quic-transport]), the specification of common log
experimentation with new techniques and their final deployment in formats and development of alternative approaches.
endpoints.
Hiding headers can limit the ability to measure and characterise 6.5. Impact on Research, Development and Deployment
traffic. Measurement data is increasingly being used to inform
design decisions in networking research, during development of new Measurement has a critical role in the design of transport protocol
mechanisms and protocols and in standardisation. Measurement has a mechanisms and their acceptance by the wider community (e.g., as a
critical role in the design of transport protocol mechanisms and method to judge the safety for Internet deployment) and is
their acceptance by the wider community (e.g., as a method to judge increasingly being used to inform design decisions in networking
the safety for Internet deployment). Observation of pathologies are research, during development of new mechanisms and protocols and in
also important in understanding the interactions between cooperating standardisation. Observation of pathologies are also important in
protocols and network mechanism, the implications of sharing capacity understanding the interactions between cooperating protocols and
with other traffic and the impact of different patterns of usage. network mechanism, the implications of sharing capacity with other
traffic and the impact of different patterns of usage.
Evolution and the ability to understand (measure) the impact need to Evolution and the ability to understand (measure) the impact need to
proceed hand-in-hand. Attention needs to be paid to the expected proceed hand-in-hand. Attention needs to be paid to the expected
scale of deployment of new protocols and protocol mechanisms. scale of deployment of new protocols and protocol mechanisms.
Whatever the mechanism, experience has shown that it is often Whatever the mechanism, experience has shown that it is often
difficult to correctly implement combination of mechanisms [RFC8085]. difficult to correctly implement combination of mechanisms [RFC8085].
These mechanisms therefore typically evolve as a protocol matures, or These mechanisms therefore typically evolve as a protocol matures, or
in response to changes in network conditions, changes in network in response to changes in network conditions, changes in network
traffic or changes to application usage. traffic or changes to application usage.
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An increased pace of evolution therefore needs to be accompanied by An increased pace of evolution therefore needs to be accompanied by
methods that can be successfully deployed and used across operational methods that can be successfully deployed and used across operational
networks. This leads to a need for network operators (at various networks. This leads to a need for network operators (at various
level (ISPs, enterprises, firewall maintainer, etc) to identify level (ISPs, enterprises, firewall maintainer, etc) to identify
appropriate operational support functions and procedures. appropriate operational support functions and procedures.
Protocols that change their transport header format (wire format) or Protocols that change their transport header format (wire format) or
their behaviour (e.g., algorithms that are needed to classify and their behaviour (e.g., algorithms that are needed to classify and
characterise the protocol), will require new tooling to be developed characterise the protocol), will require new tooling to be developed
to catch-up with the changes. If the currently deployed tools and to catch-up with the changes. If the currently deployed tools and
methods are no longer relevant then it may no longer be posisble to methods are no longer relevant then it may no longer be possible to
correctly measure performance. This can increase the response-time correctly measure performance. This can increase the response-time
after faults, and can impact the ability to manage the network after faults, and can impact the ability to manage the network
resulting in traffic causing traffic to be treated inappropriately resulting in traffic causing traffic to be treated inappropriately
(e.g., rate limiting because of being incorrectly classified/ (e.g., rate limiting because of being incorrectly classified/
monitored). monitored).
There are benefits in exposing consistent information to the network There are benefits in exposing consistent information to the network
that avoids traffic being mis-classified and then receiving a default that avoids traffic being mis-classified and then receiving a default
treatment by the network. The flow label and DSCP fields provide treatment by the network. The flow label and DSCP fields provide
examples of how transport information can be made available for examples of how transport information can be made available for
network-layer decisions. Extension headers could also be used to network-layer decisions. Extension headers could also be used to
carry transport information that can inform network-layer decisions. carry transport information that can inform network-layer decisions.
As a part of its design a new protocol specification therefore needs As a part of its design a new protocol specification therefore needs
to weigh the benefits of ossifying common headers, versus the to weigh the benefits of ossifying common headers, versus the
potential demerits of exposing specific information that could be potential demerits of exposing specific information that could be
observed along the network path, to provide tools to manage new observed along the network path, to provide tools to manage new
variants of protocols. This can be done for the entire transport variants of protocols. This can be done for the entire transport
header, or by dividing header fields between those that are header, or by dividing header fields between those that are
observable and mutable; those that are observable, but imutable; and observable and mutable; those that are observable, but immutable; and
those that are hidden/obfusticated. those that are hidden/obfusticated.
Several scenarios to illustrate different ways this could evolve are Several scenarios to illustrate different ways this could evolve are
provided below: provided below:
o One scenario is when transport protocols provide consistent o One scenario is when transport protocols provide consistent
information to the network by intentionally exposing a part of the information to the network by intentionally exposing a part of the
transport header. The design fixes the format of this information transport header. The design fixes the format of this information
between versions of the protocol. This ossification of the between versions of the protocol. This ossification of the
transport header allows an operator to establish tooling and transport header allows an operator to establish tooling and
procedures that enable it to provide consistent traffic management procedures that enable it to provide consistent traffic management
as the protocol evolves. In contrast to TCP (where all protocol as the protocol evolves. In contrast to TCP (where all protocol
information is exposed), evolution of the transport is facilitated information is exposed), evolution of the transport is facilitated
by providing cryptographic integrity checks of the transport by providing cryptographic integrity checks of the transport
header fields (preventing undetected middlebox changes) and header fields (preventing undetected middlebox changes) and
encryption of other protocol information (preventing observation encryption of other protocol information (preventing observation
within the network, or incentivising the use of the exposed within the network, or providing incentives for the use of the
information, rather than inferring information from other exposed information, rather than inferring information from other
characteristics of the flow traffic). The exposed transport characteristics of the flow traffic). The exposed transport
information can be used by operators to provide troubleshooting, information can be used by operators to provide troubleshooting,
measurement and any necessary functions appropriate to the class measurement and any necessary functions appropriate to the class
of traffic (priority, retransmission, reordering, circuit of traffic (priority, retransmission, reordering, circuit
breakers, etc). breakers, etc).
o An alternative scenario adopts different design goals, with a o An alternative scenario adopts different design goals, with a
different outcome. A protocol that encrypts all header different outcome. A protocol that encrypts all header
information forces network operators to act independently from information forces network operators to act independently from
apps/transport developments to extract the information they need apps/transport developments to extract the information they need
skipping to change at page 31, line 51 skipping to change at page 33, line 27
transport protocols. Issues relating to security are discussed in transport protocols. Issues relating to security are discussed in
the various sections of the document. the various sections of the 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 protocol or layer on top of the transport protocol
[I-D.ietf-taps-transport-security]. [I-D.ietf-taps-transport-security].
Confidentiality and strong integrity checks have properties that can Confidentiality and strong integrity checks have properties that can
also be incorporated into the deisgn of a transport protocol. also be incorporated into the design of a transport protocol.
Integrity checks can protect an endpoint from undetected modification Integrity checks can protect an endpoint from undetected modification
of protocol fields by network devices, whereas encryption and of protocol fields by network devices, whereas encryption and
obfuscation or greasing can further prevent these headers being obfuscation or greasing can further prevent these headers being
utilised by network devices. Hiding headers can therefore provide utilised by network devices. Hiding headers can therefore provide
the opportunity for greater freedom to update the protocols and can the opportunity for greater freedom to update the protocols and can
ease experimentation with new techniques and their final deployment ease experimentation with new techniques and their final deployment
in endpoints. A protocol specification needs to weigh the benefits in endpoints. A protocol specification needs to weigh the benefits
of ossifying common headers, versus the potential demerits of of ossifying common headers, versus the potential demerits of
exposing specific information that could be observed along the exposing specific information that could be observed along the
network path to provide tools to manage new variants of protocols. network path to provide tools to manage new variants of protocols.
skipping to change at page 32, line 52 skipping to change at page 34, line 27
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 may not finally be delivered by the data in the attacking packet may 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
information is accepted by a receiver or obfusticate the accepted information is accepted by a receiver or obfuscate the accepted
header information, e.g., setting a non-predictable initial value for header information, e.g., setting a non-predictable initial value for
a sequence number during a protocol handshake, as in [RFC3550] and a sequence number during a protocol handshake, as in [RFC3550] and
[RFC6056], or a port value that can not be predicted (see section 5.1 [RFC6056], or a port value that can not 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 check before accepting packets at the to be used as a part of check before accepting packets at the
transport layer (e.g., utilising a part of the sequence number space transport layer (e.g., utilising a part of the sequence number space
that is encrypted; or by verifying an encrypted token not visible to that is encrypted; or by verifying an encrypted token not visible to
an attacker). This would also mitigate on-path attacks. An an attacker). This would also mitigate on-path attacks. An
additional processing cost can be incurred when decryption needs to additional processing cost can be incurred when decryption needs to
be attempted before a receiver is able to discard injected packets. be attempted before a receiver is able to discard injected packets.
skipping to change at page 33, line 34 skipping to change at page 35, line 15
9. IANA Considerations 9. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX XX RFC ED - PLEASE REMOVE THIS SECTION XXX
This memo includes no request to IANA. This memo includes no request to IANA.
10. Acknowledgements 10. Acknowledgements
The authors would like to thank Mohamed Boucadair, Spencer Dawkins, The authors would like to thank Mohamed Boucadair, Spencer Dawkins,
Tom Herbert, Jana Iyengar, Mirja Kuehlewind, Kyle Rose, Kathleen Tom Herbert, Jana Iyengar, Mirja Kuehlewind, Kyle Rose, Kathleen
Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, and other Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, Chris
members of the TSVWG for their comments and feedback. Wood, and other members of the TSVWG for their comments and feedback.
This work has received funding from the European Union's Horizon 2020 This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No 688421.The research and innovation programme under grant agreement No 688421.The
opinions expressed and arguments employed reflect only the authors' opinions expressed and arguments employed reflect only the authors'
view. The European Commission is not responsible for any use that view. The European Commission is not responsible for any use that
may be made of that information. may be made of that information.
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.
skipping to change at page 34, line 12 skipping to change at page 35, line 41
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-ippm-ioam-data] [I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., Pignataro, C., Gredler, H., Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon, P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
"Data Fields for In-situ OAM", draft-ietf-ippm-ioam- "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
data-03 (work in progress), June 2018. data-03 (work in progress), June 2018.
[I-D.ietf-quic-spin-exp]
Trammell, B. and M. Kuehlewind, "The QUIC Latency Spin
Bit", draft-ietf-quic-spin-exp-01 (work in progress),
October 2018.
[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-14 (work and Secure Transport", draft-ietf-quic-transport-14 (work
in progress), August 2018. in progress), August 2018.
[I-D.ietf-rtcweb-overview] [I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-19 Browser-based Applications", draft-ietf-rtcweb-overview-19
(work in progress), November 2017. (work in progress), November 2017.
skipping to change at page 34, line 33 skipping to change at page 36, line 21
Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey
of Transport Security Protocols", draft-ietf-taps- of Transport Security Protocols", draft-ietf-taps-
transport-security-02 (work in progress), June 2018. transport-security-02 (work in progress), June 2018.
[I-D.ietf-tcpinc-tcpcrypt] [I-D.ietf-tcpinc-tcpcrypt]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack, Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic protection of TCP Streams Q., and E. Smith, "Cryptographic protection of TCP Streams
(tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-12 (work in (tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-12 (work in
progress), June 2018. progress), June 2018.
[I-D.ietf-tsvwg-l4s-arch]
Briscoe, B., Schepper, K., and M. Bagnulo, "Low Latency,
Low Loss, Scalable Throughput (L4S) Internet Service:
Architecture", draft-ietf-tsvwg-l4s-arch-02 (work in
progress), March 2018.
[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.thomson-quic-grease] [I-D.thomson-quic-grease]
Thomson, M., "More Apparent Randomization for QUIC", Thomson, M., "More Apparent Randomization for QUIC",
draft-thomson-quic-grease-00 (work in progress), December draft-thomson-quic-grease-00 (work in progress), December
2017. 2017.
skipping to change at page 35, line 18 skipping to change at page 36, line 49
progress), April 2018. progress), April 2018.
[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.
[Measure] Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement- [Measure] Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement-
based Protocol Design, Eur. Conf. on Networks and based Protocol Design, Eur. Conf. on Networks and
Communications, Oulu, Finland.", June 2017. Communications, Oulu, Finland.", June 2017.
[Quic-Trace]
"https:QUIC trace utilities //github.com/google/quic-
trace".
[RFC1273] Schwartz, M., "Measurement Study of Changes in Service- [RFC1273] Schwartz, M., "Measurement Study of Changes in Service-
Level Reachability in the Global TCP/IP Internet: Goals, Level Reachability in the Global TCP/IP Internet: Goals,
Experimental Design, Implementation, and Policy Experimental Design, Implementation, and Policy
Considerations", RFC 1273, DOI 10.17487/RFC1273, November Considerations", RFC 1273, DOI 10.17487/RFC1273, November
1991, <https://www.rfc-editor.org/info/rfc1273>. 1991, <https://www.rfc-editor.org/info/rfc1273>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998, DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>. <https://www.rfc-editor.org/info/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>.
[RFC2507] Degermark, M., Nordgren, B., and S. Pink, "IP Header [RFC2507] Degermark, M., Nordgren, B., and S. Pink, "IP Header
Compression", RFC 2507, DOI 10.17487/RFC2507, February Compression", RFC 2507, DOI 10.17487/RFC2507, February
1999, <https://www.rfc-editor.org/info/rfc2507>. 1999, <https://www.rfc-editor.org/info/rfc2507>.
[RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP [RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
Headers for Low-Speed Serial Links", RFC 2508, Headers for Low-Speed Serial Links", RFC 2508,
DOI 10.17487/RFC2508, February 1999, DOI 10.17487/RFC2508, February 1999,
<https://www.rfc-editor.org/info/rfc2508>. <https://www.rfc-editor.org/info/rfc2508>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
skipping to change at page 37, line 45 skipping to change at page 39, line 41
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>. January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437, "IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011, DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>. <https://www.rfc-editor.org/info/rfc6437>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[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>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>. 2015, <https://www.rfc-editor.org/info/rfc7525>.
skipping to change at page 40, line 49 skipping to change at page 42, line 49
giving some examples of why ossification has been an issue. giving some examples of why ossification has been an issue.
-01 This resolved some reference issues. Updated section on -01 This resolved some reference issues. Updated section on
observation by devices on the path. observation by devices on the path.
-02 Comments received from Kyle Rose, Spencer Dawkins and Tom -02 Comments received from Kyle Rose, Spencer Dawkins and Tom
Herbert. The network-layer information has also been re-organised Herbert. The network-layer information has also been re-organised
after comments at IETF-103. after comments at IETF-103.
-03 Added a section on header compression and rewriting of sections -03 Added a section on header compression and rewriting of sections
refering to RTP transport. This version contains author editorial referring to RTP transport. This version contains author editorial
work and removed duplicate section. work and removed duplicate section.
-04 Revised following SecDir Review
o Added some text on TLS story (additional input sought on relevant
considerations).
o Section 2, paragraph 8 - changed to be clearer, in particular,
added "Encryption with secure key distribution prevents"
o Flow label description rewritten based on PDS/BCP RFCs.
o Clarify requirements from RFCs concerning the IPv6 flow label and
highlight ways it can be used with encryption. (section 3.1.3)
o Add text on the explicit spin-bit work in the QUIC DT. Added
greasing of spin-bit. (Section 6.1)
o Updated section 6 and added more explanation of impact on
operators.
o Other comments addressed.
Authors' Addresses 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
 End of changes. 45 change blocks. 
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