draft-ietf-tsvwg-transport-encrypt-07.txt   draft-ietf-tsvwg-transport-encrypt-08.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: January 5, 2020 University of Glasgow Expires: February 24, 2020 University of Glasgow
July 04, 2019 August 23, 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-07 draft-ietf-tsvwg-transport-encrypt-08
Abstract Abstract
This document describes implications of applying end-to-end This document describes some implications of applying end-to-end
encryption at the transport layer. It identifies in-network uses of encryption at the transport layer. It first identifies in-network
transport layer header information. It then reviews the implications uses of transport layer header information. Then, it reviews some
of developing end-to-end transport protocols that use authentication implications of developing end-to-end transport protocols that use
to protect the integrity of transport information or encryption to encryption to provide confidentiality of the transport protocol
provide confidentiality of the transport protocol header and expected headers, or that use authentication to protect the integrity of
implications of transport protocol design and network operation. transport header information. Since measurement and analysis of the
Since transport measurement and analysis of the impact of network impact of network characteristics on transport protocols has been
characteristics have been important to the design of current important to the design of current transports, it also considers the
transport protocols, it also considers the impact on transport and impact of transport encryption on transport and application
application evolution. evolution.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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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 January 5, 2020. This Internet-Draft will expire on February 24, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 3, line 5 skipping to change at page 3, line 5
1. Introduction 1. Introduction
There is increased interest in, and deployment of, protocols that There is increased interest in, and deployment of, 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
this document strongly supports the increased use of encryption in this document strongly supports the increased use of encryption in
transport protocols. Encryption can also be used to prevent unwanted transport protocols. Encryption and authentication can also be used
modification of transport header information by middleboxes. There to prevent unwanted modification of transport header information by
are also, however, some costs, in that the widespread use of middleboxes. There are also, however, some costs, in that the
transport encryption requires changes to network operations, and widespread use of transport encryption requires changes to network
complicates network measurement for research, operational, and operations, and complicates network measurement for research,
standardisation purposes. The direction in which the use of operational, and standardisation purposes. The direction in which
transport header confidentiality evolves could have significant the use of transport header confidentiality evolves could have
implications on the way the Internet architecture develops, and significant implications on the way the Internet architecture
therefore needs to be considered as a part of protocol design. develops, and therefore needs to be considered as a part of protocol
design.
The remainder of this document discusses some consequences of The remainder of this document discusses some consequences of
applying end-to-end encryption at the transport layer. It reviews applying end-to-end encryption at the transport layer. It reviews
the implications of developing end-to-end transport protocols that the implications of developing end-to-end transport protocols that
use encryption to provide confidentiality of the transport protocol use encryption to provide confidentiality of the transport protocol
header, and considers the effect of such changes on transport headers, and considers the effect of such changes on transport
protocol design and network operations. It also considers protocol design and network operations. It also considers some
anticipated implications on transport and application evolution. anticipated implications on transport and application evolution.
Transports are also increasingly encrypting and authenticating the Transports are also increasingly encrypting and authenticating the
payload (i.e., the application data carried within the transport payload (i.e., the application data carried within the transport
connection) end-to-end. Such protection is encouraged, and the connection) end-to-end. Such protection is encouraged, and the
implications of protecting the payload are not further discussed in implications of protecting the payload are not further discussed in
this memo. this document.
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 (transport endpoints). This protocols, running on the end systems (transport endpoints). This
simple architectural view hides one of the core functions of the simple architectural view hides one of the core functions of the
transport: to discover and adapt to the Internet path that is transport: to discover and adapt to the Internet path that is
currently used. The design of Internet transport protocols is as currently used. The design of Internet transport protocols is as
much about trying to avoid the unwanted side effects of congestion on much about trying to avoid the unwanted side effects of congestion on
a flow and other capacity-sharing flows, avoiding congestion a flow and other capacity-sharing flows, avoiding congestion
collapse, adapting to changes in the path characteristics, etc., as collapse, adapting to changes in the path characteristics, etc., as
it is about end-to-end feature negotiation, flow control and it is about end-to-end feature negotiation, flow control, and
optimising for performance of a specific application. optimising for performance of a specific application.
To achieve stable Internet operations the IETF transport community To achieve stable Internet operations, the IETF transport community
has to date relied heavily on measurement and the insights of the has to date relied heavily on the results of measurements and the
network operations community to understand the trade-offs, and to insights of the network operations community to understand the trade-
inform selection of appropriate mechanisms, to ensure a safe, offs, and to inform selection of appropriate mechanisms to ensure a
reliable, and robust Internet (e.g., [RFC1273]). In turn, the safe, reliable, and robust Internet (e.g., [RFC1273]). In turn, the
network operator (and access provider) community has relied on being network operator and access provider community has relied on being
able to understand the pattern and requirements of traffic passing able to understand the pattern and requirements of traffic passing
over the Internet, both in aggregate and at the flow level. over the Internet, both in aggregate and at the flow level. The
widespread use of transport header encryption may change this.
2.1. Use of Transport Header Information in the Network 2.1. Use of Transport Header Information in the Network
In-network measurement of transport flow characteristics can be used In-network measurement of transport flow characteristics can be used
to enhance performance, and control cost and service reliability. to enhance performance, and control cost and service reliability.
Some operators have deployed functionality in middleboxes to both Some operators have deployed functionality in middleboxes to both
support network operations can be deployed to enhance performance. A support network operations and enhance performance. This reliance on
reliance on the presence and semantics of specific header information the presence and semantics of specific header information leads to
leads to ossification, where an endpoint could be required to supply ossification, where an endpoint could be required to supply a
a specific header to receive the network service that it desires. In specific header to receive the network service that it desires. In
some case this could be benign or advantageous to the protocol (e.g., some cases, this could be benign or advantageous to the protocol
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 the semantics from other flow properties). In other cases, the
ossification could frustrate the evolution of the protocol (e.g., a ossification could frustrate the evolution of the protocol (e.g., a
mechanism implemented in a network device, such as a firewall, that mechanism implemented in a network device, such as a firewall, that
required a header field to have only a specific known set of values required a header field to have only a specific known set of values
would prevent the device from forwarding packets using a different would prevent the device from forwarding packets using a different
version of a protocol that introduces a feature that changes the version of a protocol that introduces a feature that changes the
value of this field). value of this field).
Experience developing Transport Layer Security [RFC8446], required a As an example of ossification, consider the experience of developing
design that recognised that deployed middleboxes relied on the Transport Layer Security (TLS) 1.3 [RFC8446]. This required a design
exposed information in Transport Layer Security (TLS) 1.2. Examples that recognised that deployed middleboxes relied on the presence of
of the impact of ossification can be found in the development of certain header filed exposed in TLS 1.2, and failed if those headers
Multipath TCP (MPTCP) and the TCP Fast Open option. The design of were changed. Other examples of the impact of ossification can be
MPTCP had to be revised to account for middleboxes, so called "TCP found in the development of Multipath TCP (MPTCP) and the TCP Fast
Normalizers", that monitor the evolution of the window advertised in Open option. The design of MPTCP had to be revised to account for
the TCP headers and that reset connections if the window does not middleboxes, so called "TCP Normalizers", that monitor the evolution
grow as expected. Similarly, TCP Fast Open has had issues with of the window advertised in the TCP headers and that reset
middleboxes that remove unknown TCP options, that drop segments with connections if the window does not grow as expected. Similarly, TCP
unknown TCP options, that drop segments that contain data and have Fast Open has had issues with middleboxes that remove unknown TCP
the SYN bit set, that drop packets with SYN/ACK that acknowledge options, that drop segments with unknown TCP options, that drop
data, or that disrupt connections that send data before the three-way segments that contain data and have the SYN bit set, that drop
handshake completes. In both cases, the issue was caused by packets with SYN/ACK that acknowledge data, or that disrupt
middleboxes that had a hard-coded understanding of transport connections that send data before the three-way handshake completes.
behaviour, and that interacted poorly with transports that tried to
change that behaviour. Other examples have included middleboxes that In all these cases, the issue was caused by middleboxes that had a
rewrite TCP sequence and acknowledgement numbers but are unaware of hard-coded understanding of transport behaviour, and that interacted
the (newer) SACK option and don't correctly rewrite selective poorly with transports that tried to change that behaviour. Other
acknowledgements to match the changes made to the fixed TCP header. examples have included middleboxes that rewrite TCP sequence and
acknowledgement numbers but are unaware of the (newer) SACK option
and don't correctly rewrite selective acknowledgements to match the
changes made to the fixed TCP header.
2.2. Encryption of Transport Header Information 2.2. Encryption of Transport Header Information
Encryption is expected to form a basis for many future transport Encryption is expected to form a basis for many future transport
protocol designs. There are many motivations for deploying encrypted protocol designs. These can be in the form of encrypted transport
transports [RFC7624] (i.e., transport protocols that use encryption protocols (i.e., transport protocols that use encryption to provide
to provide confidentiality of some or all of the transport-layer confidentiality of some or all of the transport-layer header
header information), and encryption of transport payloads (i.e. information), and/or the encryption of transport payloads (i.e.,
Confidentiality of the payload data). Increasing public concerns confidentiality of the payload data). There are many motivations for
about interference with Internet traffic have led to a rapidly deploying such transports, and increasing public concerns about
expanding deployment of encryption to protect end-user privacy, e.g., interference with Internet traffic [RFC7624] have led to a rapidly
QUIC [I-D.ietf-quic-transport]. Using encryption to provide expanding deployment of encrypted transport protocols such as QUIC
[I-D.ietf-quic-transport]. Using encryption to provide
confidentiality of the transport layer therefore brings some well- confidentiality of the transport layer therefore brings some well-
known privacy and security benefits. Although it is important that known privacy and security benefits.
protocols either do not expose information where the usage could
change in future protocols or that methods that utilise the
information are robust to potential changes as protocols evolve over
time.
Introducing cryptographic integrity checks for header fields can Authentication and the introduction of cryptographic integrity checks
prevent undetected manipulation of the field by network devices, or for header fields can prevent undetected manipulation of transport
undetected addition of information to a packet. This does not headers by network devices. This does not prevent inspection of the
prevent inspection of the information by a device on path, and it is information by devices on path, and it is possible that such devices
possible that such devices could develop mechanisms that rely on the could develop mechanisms that rely on the presence of such a field or
presence of such a field or a known value in the field. In this a known value in the field. In this context, specification of a non-
context, specification of a non-encrypted transport header field encrypted transport header field explicitly allows protocol designers
explicitly allows protocol designers to make specific header to make the certain header information observable by the network.
information observable in the network. This supports other uses of This supports use of this information by on-path devices, but at the
this information by on-path devices, and at the same time this can be same time can be expected to lead to ossification of the transport
expected to lead to ossification of the transport header, because header, because network forwarding could evolve to depend on the
network forwarding could evolve to depend on the presence and/or presence and/or value of these fields. To avoid unwanted inspection,
value of these fields. To avoid unwanted inspection, a protocol a protocol could intentionally vary the format or value of exposed
could intentionally vary the format and/or value of exposed header header fields [I-D.ietf-tls-grease].
fields (sometimes known as Greasing [I-D.thomson-quic-grease]).
A protocol design that uses header encryption with secure key A protocol design that uses header encryption with secure key
distribution can provide confidentiality of some or all of the distribution can provide confidentiality for some, or all, of the
protocol header information. This prevents an on-path device from protocol header information. This prevents an on-path device from
observing the header field. This prevents mechanisms being built observing the transport headers, and stops mechanisms being built
that directly rely on the information or seek to infer semantics of that directly rely on transport header information, or that seek to
an exposed header field and can therefore help reduce ossification of infer semantics of exposed header fields. Transport header
the transport layer. While encryption can hide transport header encryption can therefore help reduce ossification of the transport
information, it does not prevent ossification of the network service. layer.
People seeking to understand network traffic could come to rely on While encryption can hide transport header information, it does not
pattern inferences and other heuristics as the basis for network prevent ossification of the network service. People seeking to
decision and to derive measurement data, creating new dependencies on understand network traffic could come to rely on pattern inferences
the transport protocol (or the patterns of traffic it can generate). and other heuristics as the basis for network decision and to derive
This use of machine-learning methods usually demands large data sets, measurement data. This can create new dependencies on the transport
presenting it own requirements for collecting and distributing the protocol, or the patterns of traffic it can generate. This use of
data. machine-learning methods usually demands large data sets, presenting
it own requirements for collecting and distributing the data.
2.3. Encryption tradeoffs 2.3. Encryption tradeoffs
The are architectural challenges and considerations in the way The are architectural challenges and considerations in the way
transport protocols are designed, and the ability to characterise and transport protocols are designed, and the ability to characterise and
compare different transport solutions [Measure]. The decision about compare different transport solutions [Measure]. The decision about
which transport headers fields are made observable offers trade-offs which transport headers fields are made observable offers trade-offs
around authentication and confidentiality versus observability, around authentication and confidentiality versus observability,
network operations and management, and ossification. The impact network operations and management, and ossification. The impact
differs depending on the activity, for example: differs depending on the activity, for example:
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Confidentiality of the transport payload could be provided while Confidentiality of the transport payload could be provided while
leaving some, or all, transport headers unencrypted (or providing leaving some, or all, transport headers unencrypted (or providing
this information in a network-layer extension), possibly with this information in a network-layer extension), possibly with
authentication. This provides many of the privacy and security authentication. This provides many of the privacy and security
benefits while supporting operations and research, but at the cost benefits while supporting operations and research, but at the cost
of ossifying the exposed headers. of ossifying the exposed headers.
Protection from Denial of Service: Observable transport headers Protection from Denial of Service: Observable transport headers
currently provide useful input to classify and detect anomalous currently provide useful input to classify and detect anomalous
events (e.g., changes in application behaviour, distributed denial events, such as changes in application behaviour or distributed
of service attacks). For this application to be effective, this denial of service attacks. For this application to be effective,
needs to be able to uniquely disambiguate unwanted traffic. it needs to be possible for an operator to uniquely disambiguate
unwanted traffic. Concealing transport header information would
Concealing transport header information would prevent separating prevent disambiguation based on transport information. This could
anomalous traffic based on transport information. This could result in less-efficient identification of unwanted traffic, the
result in less-efficient identification of unwanted traffic or use of heuristics to identify anomalous flows, or the introduction
development of different methods (e.g. rate-limiting of of rate limits for uncharacterised traffic.
uncharacterised traffic). Additional mechanisms will need to be
introduced, such as heuristics to disambiguate any unwanted
traffic.
Network Troubleshooting and Diagnostics: Observable transport Network Troubleshooting and Diagnostics: Observable transport
headers can be used by operators to support network headers can be utilised by operators for network troubleshooting
troubleshooting and diagnostics. A flow experiencing packet loss and diagnostics. Flows experiencing packet loss or jitter are
or jitter looks like an unaffected flow when only observing hard to distinguish from unaffected flows when only observing
network layer headers. network layer headers. Effective troubleshooting often requires
visibility into the transport layer behaviour.
Concealing transport header information eliminates the incentive Concealing transport header information reduces the incentive for
for operators to troubleshoot, since they cannot interpret the operators to troubleshoot, since they cannot interpret the data.
data. It can limit understanding of transport dynamics, such as It can limit understanding of transport dynamics, such as the
the impact of packet loss or latency on the flows, or localizing impact of packet loss or latency on the flows, or make it harder
the network segment causing the packet loss or latency. to localise the network segment intoducing the packet loss or
Additional mechanisms will be needed to help reconstruct or latency. Additional mechanisms will be needed to help reconstruct
replace transport-level metrics for troubleshooting and or replace transport-level metrics for troubleshooting and
diagnostics. These can add complexity and operational costs diagnostics. These can add complexity and operational costs
(e.g., in deploying additional functions in equipment or adding (e.g., in deploying additional functions in equipment or adding
traffic overhead). traffic overhead).
Network Traffic Analysis: Observable transport headers can support Network Traffic Analysis: Observable transport headers can support
network traffic analysis to determine which transport protocols network traffic analysis to determine which transport protocols
and features are being used across a network segment and to and features are being used across a network segment and to
measure trends in the pattern of usage. For some applications measure trends in the pattern of usage. For some applications
end-to-end measurements/traces are sufficient, in other end-to-end measurements/traces are sufficient, but in other
applications it is important to relate observations to specific applications it is important to relate observations to specific
equipment/configurations or network segments. equipment/configurations or particular network segments.
Concealing transport header information can make analysis harder Concealing transport header information can make analysis harder
or impossible. This could impact the ability for an operator to or impossible. This could impact the ability for an operator to
anticipate the need for network upgrades and roll-out. It can anticipate the need for network upgrades and roll-out. It can
also impact the on-going traffic engineering activities performed also impact the on-going traffic engineering activities performed
by operators (such as determining which parts of the path by operators, such as determining which parts of the path
contribute delay, jitter or loss). While this impact could, in contribute delay, jitter or loss. While this impact could, in
many cases, be small, there are scenarios where operators directly many cases, be small, there are scenarios where operators directly
support particular services (e.g., to explore issues relating to support particular services and need visibility to explore issues
Quality of Service, QoS; the ability to perform fast re-routing of relating to Quality of Service (QoS), the ability to perform fast
critical traffic, or support to mitigate the characteristics of re-routing of critical traffic, or to mitigate the characteristics
specific radio links). The more complex the underlying of specific radio links, and so on.
infrastructure the more important this impact.
Open and Verifiable Network Data: Observable transport headers can Open and Verifiable Network Data: Observable transport headers can
provide open and verifiable measurement data. The ability of provide open and verifiable measurement data. The ability of
other stake holders to review transport header traces helps other stake holders to review transport header traces helps
develop insight into performance and traffic contribution of develop insight into performance and traffic contribution of
specific variants of a protocol. Independently observed data is specific variants of a protocol. Independently observed data is
important to help ensure the health of the research and important to help ensure the health of the research and
development communities. development communities.
Concealing transport header information can reduce the range of Concealing transport header information can reduce the range of
actors that observe useful data. This would limit the information actors that can observe useful data. This would limit the
sources available to the Internet community to understand the information sources available to the Internet community to
operation of new transport protocols, reducing information to understand the operation of new transport protocols, reducing
inform design decisions and standardisation of the new protocols information to inform design decisions and standardisation of the
and related operational practices. new protocols and related operational practices.
Compliance: Observable transport headers coupled with published Compliance: Observable transport headers coupled with published
transport specifications allow operators and regulators to check transport specifications allow operators and regulators to check
compliance. Independently verifiable performance metrics can also compliance. Independently verifiable performance metrics can also
be utilised to demonstrate regulatory compliance in some be utilised to demonstrate regulatory compliance in some
jurisdictions, and as a basis for informing design decisions. jurisdictions, and as a basis for informing design decisions.
This can bring assurance to those operating networks, often This can bring assurance to those operating networks, often
avoiding the need to deploy complex techniques that routinely avoiding the need to deploy complex techniques that routinely
monitor and manage Internet traffic flows (e.g., avoiding the monitor and manage Internet traffic flows (e.g., avoiding the
capital and operational costs of deploying flow rate-limiting and capital and operational costs of deploying flow rate-limiting and
network circuit-breaker methods [RFC8084]). network circuit-breaker methods [RFC8084]).
When transport header information is concealed, it is not possible When transport header information is concealed, it is not possible
to observe transport header information. Methods are still needed to observe transport header information. Methods are still needed
to confirm that the traffic produced conforms to the expectations to confirm that the traffic produced conforms to the expectations
of the operator or developer. of the operator or developer.
Different parties will view the relative importance of these issues
differently. For some, the benefits of encrypting some, or all, of
the transport headers may outweigh the impact of doing so; others
might make a different trade-off. The purpose of highlighting the
trade-offs is to make such analysis possible.
3. Current uses of Transport Headers within the Network 3. Current uses of Transport Headers within the Network
Despite transport headers having end-to-end meaning, some of these Despite transport headers having end-to-end meaning, some of these
transport headers have come to be used in various ways within the transport headers have come to be used in various ways within the
Internet. In response to pervasive monitoring [RFC7624] revelations Internet. In response to pervasive monitoring [RFC7624] revelations
and the IETF consensus that "Pervasive Monitoring is an Attack" and the IETF consensus that "Pervasive Monitoring is an Attack"
[RFC7258], efforts are underway to increase encryption of Internet [RFC7258], efforts are underway to increase encryption of Internet
traffic. Applying confidentiality to transport header fields would traffic. Applying confidentiality to transport header fields affects
affect how protocol information is used [RFC8404]. To understand how protocol information is used [RFC8404], requiring consideration
these implications, it is first necessary to understand how transport of the trade-offs discussed in Section 2.3. To understand the
layer headers are currently observed and/or modified by middleboxes implications, it is necessary to understand how transport layer
within the network. headers are currently observed and/or modified by middleboxes within
the network.
Transport protocols can be designed to encrypt or authenticate We review some current uses in the following section. This does not
transport header fields. Authentication at the transport layer can consider the intentional modification of transport headers by
be used to detect any changes to an immutable header field that were middleboxes (such as in Network Address Translation, NAT, or
made by a network device along a path. The intentional modification Firewalls). Common issues concerning IP address sharing are
of transport headers by middleboxes (such as Network Address described in [RFC6269].
Translation, NAT, or Firewalls) is not considered. Common issues
concerning IP address sharing are described in [RFC6269].
3.1. Observing Transport Information in the Network 3.1. Observing Transport Information in the Network
If in-network observation of transport protocol headers is needed, If in-network observation of transport protocol headers is needed,
this requires knowledge of the format of the transport header: this requires knowledge of the format of the transport header:
o Flows need to be identified at the level required to perform the o Flows need to be identified at the level required to perform the
observation; observation;
o The protocol and version of the header need to be visible, e.g., o The protocol and version of the header need to be visible, e.g.,
by defining the wire image [I-D.trammell-wire-image]. As by defining the wire image [RFC8546]. As protocols evolve over
protocols evolve over time and there could be a need to introduce time and there could be a need to introduce new transport headers.
new transport headers. This could require interpretation of This could require interpretation of protocol version information
protocol version information or connection setup information; or connection setup information;
o The location and syntax of any observed transport headers need to o The location and syntax of any observed transport headers need to
be known. IETF transport protocols can specify this information. be known. IETF transport protocols can specify this information.
The following subsections describe various ways that observable The following subsections describe various ways that observable
transport information has been utilised. transport information has been utilised.
3.1.1. Flow Identification 3.1.1. Flow Identification Using Transport Layer Headers
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. This becomes more complex and less easily Service, DOS, prevention. This 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.
Observable transport header information (together with information in Observable transport header information, together with information in
the network header), has been used to identify a flow and the the network header, has been used to identify flows and their
connection state of the flow, together with the protocol options connection state, together with the protocol options being used.
being used. In some usages, a low-numbered (well-known) transport
port number has been used to identify a protocol (although port
information alone is not sufficient to guarantee identification of a
protocol, since applications can use arbitrary ports, multiple
sessions can be multiplexed on a single port, and ports can be re-
used by subsequent sessions).
Transport protocols, such as TCP and the Stream Control Transport Transport protocols, such as TCP and the Stream Control Transport
Protocol (SCTP) specify a standard base header that includes sequence Protocol (SCTP), specify a standard base header that includes
number information and other data, with the possibility to negotiate sequence number information and other data. They also have the
additional headers at connection setup, identified by an option possibility to negotiate additional headers at connection setup,
number in the transport header. UDP-based protocols can use, but identified by an option number in the transport header.
sometimes do not use, well-known port numbers. Some flows can
instead be identified by observing signalling protocol data (e.g., In some uses, a low-numbered (well-known) transport port number can
[RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of magic be used to identify the protocol, although port information alone is
numbers placed in the first byte(s) of the datagram payload not sufficient to guarantee identification of a protocol since
applications can use arbitrary ports, multiple sessions can be
multiplexed on a single port, and ports can be re-used by subsequent
sessions.
UDP-based protocols often do not use well-known port numbers. Some
flows can instead be identified by observing signalling protocol data
(e.g., [RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of
magic numbers placed in the first byte(s) of the datagram payload
[RFC7983]. [RFC7983].
Concealing transport header information can remove information used Concealing transport header information can remove information used
to classify flows by passive observers along the path and operators to classify flows by passive observers along the path, so operators
will be unable to use this information directly. Careful use of the will be unable to use this information directly. Careful use of the
network layer features can help address provide similar information network layer features can help address provide similar information
in the case where the network is unable to inspect transport protocol in the case where the network is unable to inspect transport protocol
headers. Operators could also turn to more ambitious ways to headers. Operators could also turn to more ambitious ways to
collect, estimate, or infer that data (for example heuristics based collect, estimate, or infer that data, including heuristics based on
on the analysis of traffic patterns). For example, an operator no the analysis of traffic patterns. For example, an operator that no
longer has access to Session Description Protocol (SDP) session longer has access to Session Description Protocol (SDP) session
descriptions to classify a flow carry as audio traffic. Instead, the descriptions to classify a flow carry as audio traffic might instead
operator might use heuristics to infer that short UDP packets with use heuristics to infer that short UDP packets with regular spacing
regular spacing carry audio traffic. Operational practices aimed at carry audio traffic. Operational practices aimed at inferring
guessing transport parameters are out of scope for this document, and transport parameters are out of scope for this document, and are only
are only mentioned here to recognize that encryption does not prevent mentioned here to recognize that encryption does not prevent
operators from attempting to apply practices that were used with operators from attempting to apply practices that were used with
unencrypted transport headers. unencrypted transport headers.
Confidentiality of the transport payload could be provided while Confidentiality of the transport payload could be provided while
leaving some, or all, transport headers unencrypted (or providing leaving some, or all, transport headers unencrypted, or providing
this information in a network-layer extension), possibly with this information in a network-layer extension, possibly with
authentication. This provides many of the privacy and security authentication. This provides many of the privacy and security
benefits while supporting operations and research, but at the cost of benefits while supporting operations and research, but at the cost of
ossifying the exposed headers. ossifying the exposed headers.
3.1.2. Metrics derived from Transport Layer Headers 3.1.2. Metrics derived from Transport Layer Headers
Observable transport headers enable explicit measure and analysis Observable transport headers enable explicit measurement and analysis
protocol performance, network anomalies, and failure pathologies at of protocol performance, network anomalies, and failure pathologies
any point along the Internet path. Some actors manage their portion at any point along the Internet path. Some operators manage their
of the Internet by characterizing the performance of link/network portion of the Internet by characterizing the performance of link/
segments. Passive monitoring can observe traffic that does not network segments. Passive monitoring can observe traffic that does
encrypt the transport header information to make inferences from not encrypt the transport header information, and make inferences
transport headers to derive these performance metrics. from transport headers to derive performance metrics.
A variety of open source and commercial tools have been deployed that A variety of open source and commercial tools have been deployed that
utilise this information. The following metrics can be derived from utilise transport header information in this way. The following
transport header information: metrics can be derived:
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., to assess endpoint or for an aggregate of endpoints (e.g., to assess
subscriber usage). It can also be used to trigger measurement- subscriber usage). It can also be used to trigger measurement-
based traffic shaping and to implement QoS support within the based traffic shaping, and to implement QoS support within the
network and lower layers. Volume measures can be valuable for network and lower layers. Volume measures can be valuable for
capacity planning and providing detail of trends, rather than the capacity planning and providing detail of trends, rather than the
volume per subscriber. volume per subscriber.
Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g., Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g.,
from transport sequence numbers) and has been used as a metric for from transport sequence numbers) and has been used as a metric for
performance assessment and to characterise transport behaviour. performance assessment and to characterise transport behaviour.
Understanding the location and root cause of loss can help an Understanding the location and root cause of loss can help an
operator determine whether this requires corrective action. operator determine whether this requires corrective action.
Network operators have used the variation in patterns of loss as a Network operators have used the variation in patterns of loss as a
key performance metric, utilising this to detect changes in the key performance metric, utilising this to detect changes in the
offered service. offered service.
There are various causes of loss, including corruption of link There are various causes of loss, including corruption of link
frames (e.g., interference on a radio link), buffer overflow frames (e.g., interference on a radio link), buffer overflow
(e.g., due to congestion), policing (traffic management), buffer (e.g., due to congestion), policing (traffic management), buffer
management (e.g., Active Queue Management, AQM [RFC7567]), and management (e.g., Active Queue Management, AQM [RFC7567]), and
inadequate provision of traffic preemption. Understanding flow inadequate provision of traffic pre-emption. Understanding flow
loss rate requires either maintaining per flow packet counters or loss rates requires either observing sequence numbers in transport
by observing sequence numbers in transport headers. Loss can be headers, or maintaining per-flow packet counters (but note that
monitored at the interface level by devices in the network. It is flow identification often requires transport header information).
often valuable to understand the conditions under which packet Per-hop loss can be monitored at the interface level by devices in
loss occurs. This usually requires relating loss to the traffic the network. It is often valuable to understand the conditions
flowing on the network node/segment at the time of loss. under which packet loss occurs. This usually requires relating
per-flow loss to the traffic flowing on the network node/segment
at the time of loss.
Observation of transport feedback information (e.g., RTP Control Observation of transport feedback information (e.g., RTP Control
Protocol (RTCP) reception reports [RFC3550], TCP SACK blocks) can Protocol (RTCP) reception reports [RFC3550], TCP SACK blocks) can
increase understanding of the impact of loss and help identify increase understanding of the impact of loss and help identify
cases where loss could have been wrongly identified, or the cases where loss could have been wrongly identified, or where the
transport did not require the lost packet. It is sometimes more transport did not require the lost packet. It is sometimes more
helpful to understand the pattern of loss, than the loss rate, helpful to understand the pattern of loss, than the loss rate,
because losses can often occur as bursts, rather than randomly- because losses can often occur as bursts, rather than randomly-
timed events. timed events.
Throughput and Goodput: The throughput achieved by a flow can be Throughput and Goodput: Throughput is the amount of data sent by a
flow per time interval. Goodput [RFC7928] is a measure of useful
data exchanged (the ratio of useful data to total volume of
traffic sent by a flow). The throughput achieved by a flow can be
determined even when transport header information is concealed, determined even when transport header information is concealed,
providing the individual flow can be identified. Goodput providing the individual flow can be identified. Goodput requires
[RFC7928] is a measure of useful data exchanged (the ratio of ability to differentiate loss and retransmission of packets, for
useful/total volume of traffic sent by a flow). This requires example by observing packet sequence numbers in the TCP or the
ability to differentiate loss and retransmission of packets (e.g., Real-time Transport Protocol (RTP) headers [RFC3550].
by observing packet sequence numbers in the TCP or the Real-time
Transport Protocol, RTP, headers [RFC3550]).
Latency: Latency is a key performance metric that impacts Latency: Latency is a key performance metric that impacts
application response time and user-perceived response time. It application and user-perceived response times. It often
often indirectly impacts throughput and flow completion time. indirectly impacts throughput and flow completion time. Latency
Latency determines the reaction time of the transport protocol determines the reaction time of the transport protocol itself,
itself, impacting flow setup, congestion control, loss recovery, impacting flow setup, congestion control, loss recovery, and other
and other transport mechanisms. The observed latency can have transport mechanisms. The observed latency can have many
many components [Latency]. Of these, unnecessary/unwanted queuing components [Latency]. Of these, unnecessary/unwanted queuing in
in network buffers has often been observed as a significant factor network buffers has often been observed as a significant factor
[bufferbloat]. Once the cause of unwanted latency has been [bufferbloat]. Once the cause of unwanted latency has been
identified, this can often be eliminated. 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 in the network to determine not only the path
RTT, but also to measure the upstream and downstream contribution RTT, but also to measure the upstream and downstream contribution
to the RTT. This could be used to locate a source of latency, to the RTT. This could be used to locate a source of latency,
e.g., by observing cases where the median RTT is much greater than e.g., by observing cases where the median RTT is much greater than
the minimum RTT for a part of a path. 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 deployment and tune information to understand the impact of configuration changes and
deployed services. Latency metrics are key to evaluating and to tune deployed services. Latency metrics are key to evaluating
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
[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
changes in packet timing (jitter). Short and long-term delay (small) changes in packet timing (jitter). Short and long-term
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 (e.g., jitter perceived quality of applications using the network. For example,
metrics are often cited when characterising paths supporting real- jitter metrics are often cited when characterising paths
time traffic). To assess the performance of such applications, it supporting real-time traffic. To assess the performance of such
can be necessary to measure the variation in delay observed along applications, it can be necessary to measure the variation in
a portion of the path [RFC3393] [RFC5481]. The requirements delay observed along a portion of the path [RFC3393] [RFC5481].
resemble those for the measurement of latency. The requirements for observable transport headers 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. Since this impacts transport performance, 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.
skipping to change at page 13, line 31 skipping to change at page 13, line 35
and provide information on the progress and quality of a session and provide information on the progress and quality of a session
using RTP. As with other measurement, metadata is often needed to using RTP. As with other measurement, metadata is often needed to
understand the context under which the data was collected, understand the context under which the data was collected,
including the time, observation point [RFC7799], and way in which including the time, observation point [RFC7799], and way in which
metrics were accumulated. The RTCP protocol directly reports some metrics were accumulated. The RTCP protocol directly reports some
of this information in a form that can be directly visible in the of this information in a form that can be directly visible in the
network. A user of summary measurement data needs to trust the network. A user of summary measurement data needs to trust the
source of this data and the method used to generate the summary source of this data and the method used to generate the summary
information. information.
This information can support network operations, e.g. to inform This information can support network operations, inform capacity
capacity planning and assist in determining the need for equipment planning, and assist in determining the need for equipment and/or
and/or configuration changes by network operators. It can also configuration changes by network operators. It can also inform
inform Internet engineering activities by informing the development Internet engineering activities by informing the development of new
of new protocols, methodologies, and procedures. protocols, methodologies, and procedures.
3.1.3. Transport use of Network Layer Header Fields 3.1.3. Transport use of Network Layer Header Fields
Information from the transport protocol can be used by a multi-field Information from the transport protocol can be used by a multi-field
classifier as a part of policy framework. Policies are commonly used classifier as a part of policy framework. Policies are commonly used
for management of the QoS or Quality of Experience (QoE) in resource- for management of the QoS or Quality of Experience (QoE) in resource-
constrained networks and by firewalls that use the information to constrained networks, and by firewalls to implement access rules (see
implement access rules (see also section 2.2.2 of [RFC8404]). also section 2.2.2 of [RFC8404]). Network-layer classification
Network-layer classification methods that rely on a multi-field methods that rely on a multi-field classifier (e.g., inferring QoS
classifier (e.g. Inferring QoS from the 5-tuple or choice of from the 5-tuple or choice of application protocol) are incompatible
application protocol) are incompatible with transport protocols that with transport protocols that encrypt the transport information.
encrypt the transport information. Traffic that cannot be Traffic that cannot be classified will typically receive a default
classified, will typically receive a default treatment. treatment.
Transport information can also be explicitly set in network-layer Transport information can also be explicitly set in network-layer
header fields that are not encrypted. This can provide information header fields that are not encrypted. This can provide information
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 The user of a transport that multiplexes multiple sub-flows might
sub-flows could wish to hide the presence and characteristics of want to hide the presence and characteristics of these sub-flows. On
these sub-flows. On the other hand, an encrypted transport could set the other hand, an encrypted transport could set the network-layer
the network-layer information to indicate the presence of sub-flows information to indicate the presence of sub-flows, and to reflect the
and to reflect the network needs of individual sub-flows. There are network needs of individual sub-flows. There are several ways this
several ways this could be done: could be done:
IP Address: Applications expose the addresses used by endpoints, and IP Address: Applications expose the addresses used by endpoints, and
this is used in the forwarding decisions in network devices. this is used in the forwarding decisions in network devices.
Address and other protocol information can be used by a Multi- Address and other protocol information can be used by a Multi-
Field (MF) classifier to determine how traffic is treated Field (MF) classifier to determine how traffic is treated
[RFC2475], and hence the quality of experience for a flow. [RFC2475], and hence the quality of experience for a flow.
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
subflows. RFC6437 provides further guidance on choosing a flow subflows. 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". To promote privacy, the a source of flow labels will choose". To promote privacy, the
Flow Label assignment needs to avoid introducing linkability that Flow Label assignment needs to avoid introducing linkability that
a network device may observe. Once set, a label can provide a network device may observe. Once set, a flow label can provide
information that can help inform network-layer queuing and information that can help inform network-layer queuing and
forwarding [RFC6438](e.g. for Equal Cost Multi-Path, ECMP, forwarding [RFC6438], for example with Equal Cost Multi-Path
routing, and Link Aggregation, LAG) [RFC6294]. [RFC6438] routing and Link Aggregation [RFC6294]. Considerations when using
describes considerations when used with IPsec. IPsec are further described in [RFC6438].
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
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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 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 Congestion equipment that implements an AQM method with CE marking of IP
Experienced (CE) marking of IP packets [RFC8087], since it can packets [RFC8087], since it can react to congestion without also
react to congestion without also having to recover from lost having to recover from lost packets.
packets.
ECN exposes the presence of congestion. The reception of CE- ECN exposes the presence of congestion. The reception of CE-
marked packets can be used to estimate the level of incipient marked packets can be used to estimate the level of incipient
congestion on the upstream portion of the path from the point of congestion on the upstream portion of the path from the point of
observation (Section 2.5 of [RFC8087]). Interpreting the marking observation (Section 2.5 of [RFC8087]). Interpreting the marking
behaviour (i.e., assessing congestion and diagnosing faults) behaviour (i.e., assessing congestion and diagnosing faults)
requires context from the transport layer (such as path RTT). requires context from the transport layer, such as path RTT.
AQM and ECN offer a range of algorithms and configuration options. AQM and ECN offer a range of algorithms and configuration options.
Tools therefore need to be available to network operators and Tools therefore need to be available to network operators and
researchers to understand the implication of configuration choices researchers to understand the implication of configuration choices
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].
When transport headers are concealed, operators will be unable to use When transport headers are concealed, operators will be unable to use
this information directly. Careful use of the network layer features this information directly. Careful use of the network layer features
can help address provide similar information in the case where the can help address provide similar information in the case where the
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3.2. Transport Measurement 3.2. Transport Measurement
The common language between network operators and application/content The common language between network operators and application/content
providers/users is packet transfer performance at a layer that all providers/users is packet transfer performance at a layer that all
can view and analyse. For most packets, this has been the transport can view and analyse. For most packets, this has been the transport
layer, until the emergence of QUIC, with the obvious exception of layer, until the emergence of QUIC, with the obvious exception of
Virtual Private Networks (VPNs) and IPsec. Virtual Private Networks (VPNs) and IPsec.
When encryption conceals more layers in each packet, people seeking When encryption conceals more layers in each packet, people seeking
understanding of the network operation rely more on pattern understanding of the network operation rely more on pattern inference
inferences and other heuristics reliance on pattern inferences and and other heuristics. It remains to be seen whether more complex
accuracy suffers. For example, the traffic patterns between server inferences can be mastered to produce the same monitoring accuracy
and browser are dependent on browser supplier and version, even when (see section 2.1.1 of [RFC8404]).
the sessions use the same server application (e.g., web e-mail
access). It remains to be seen whether more complex inferences can
be mastered to produce the same monitoring accuracy (see section
2.1.1 of [RFC8404]).
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, is endpoints, additional metadata, such as the state of the network, is
often required to interpret this data to answer questions about often required to interpret this data to answer questions about
network performance or understand a pathology. Collecting and network performance or understand a pathology. Collecting and
coordinating such metadata is more difficult when the observation coordinating such metadata is more difficult when the observation
point is at a different location to the bottleneck/device under point is at a different location to the bottleneck/device under
evaluation [RFC7799]. evaluation [RFC7799].
Packet sampling techniques are used to scale the processing involved Packet sampling techniques are used to scale the processing involved
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Sometimes multiple on-path observation points are needed. By Sometimes multiple on-path observation points are needed. By
correlating observations of headers at multiple points along the path correlating observations of headers at multiple points along the path
(e.g., at the ingress and egress of a network segment), an observer (e.g., at the ingress and egress of a network segment), an observer
can determine the contribution of a portion of the path to an can determine the contribution of a portion of the path to an
observed metric, to locate a source of delay, jitter, loss, observed metric, to locate a source of delay, jitter, loss,
reordering, congestion marking, etc. reordering, congestion marking, etc.
3.2.2. Use by Operators to Plan and Provision Networks 3.2.2. Use by Operators to Plan and Provision Networks
Traffic measurements (e.g., traffic volume, loss, latency) is used by Traffic measurements (e.g., traffic volume, loss, latency) are used
operators to help plan deployment of new equipment and configuration by operators to help plan deployment of new equipment and
in their networks. Data is also valuable to equipment vendors who configuration in their networks. Data is also valuable to equipment
want to understand traffic trends and patterns of usage as inputs to vendors who want to understand traffic trends and patterns of usage
decisions about planning products and provisioning for new as inputs to decisions about planning products and provisioning for
deployments. This measurement information can also be correlated new deployments. This measurement information can also be correlated
with billing information when this is also collected by an operator. with billing information when this is also collected by an operator.
A network operator supporting traffic that uses transport header A network operator supporting traffic that uses transport header
encryption might not have access to per-flow measurement data. encryption might not have access to per-flow measurement data.
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 it may be impossible to correlate endpoint addresses being used, but it may be impossible to correlate
patterns in measurements with changes in transport protocols (e.g., patterns in measurements with changes in transport protocols (e.g.,
the impact of changes in introducing a new transport protocol the impact of changes in introducing a new transport protocol
mechanism). This increases the dependency on other indirect sources mechanism). This increases the dependency on other indirect sources
of information to inform planning and provisioning. of information to inform planning and provisioning.
3.2.3. Service Performance Measurement 3.2.3. Service Performance Measurement
Traffic measurements (e.g., traffic volume, loss, latency) can be Traffic measurements (e.g., traffic volume, loss, latency) can be
used by various actors to help analyse the performance offered to the used by various actors to help analyse the performance offered to the
users of a network segment, and to inform operational practice. users of a network segment, and to inform operational practice.
While active measurements (see section 3.4 of [RFC7799]) may be used While active measurements (see section 3.4 of [RFC7799]) may be used
within a network, passive measurements (see section 3.6 of [RFC7799] within a network, passive measurements (see section 3.6 of [RFC7799])
) can have advantages in terms of eliminating unproductive test can have advantages in terms of eliminating unproductive test
traffic, reducing the influence of test traffic on the overall traffic, reducing the influence of test traffic on the overall
traffic mix, and the ability to choose the point of observation (see traffic mix, and the ability to choose the point of observation (see
Section 3.2.1). However, passive measurements can rely on observing Section 3.2.1). However, passive measurements can rely on observing
transport headers which is not possible if those headers are transport headers which is not possible if those headers are
encrypted. encrypted.
3.2.4. Measuring Transport to Support Network Operations 3.2.4. Measuring Transport to Support Network Operations
Information provided by tools observing transport headers can help Information provided by tools observing transport headers can help
determine whether mechanisms are needed in the network to prevent determine whether mechanisms are needed in the network to prevent
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impact of specific transport protocols (or protocol mechanisms) on impact of specific transport protocols (or protocol mechanisms) on
the other traffic that shares a network. An observation in the the other traffic that shares a network. An observation in the
network can gain an understanding of the dynamics of a flow and network can gain an understanding of the dynamics of a flow and
its congestion control behaviour. Analysing observed flows can its congestion control behaviour. Analysing observed flows can
help to build confidence that an application flow backs-off its help to build confidence that an application flow backs-off its
share of the network load in the face of persistent congestion, share of the network load in the face of persistent congestion,
and hence to understand whether the behaviour is appropriate for and hence to understand whether the behaviour is appropriate for
sharing limited network capacity. For example, it is common to sharing limited network capacity. For example, it is common to
visualise plots of TCP sequence numbers versus time for a flow to visualise plots of TCP sequence numbers versus time for a flow to
understand how a flow shares available capacity, deduce its understand how a flow shares available capacity, deduce its
dynamics in response to congestion, etc. The ability to identify dynamics in response to congestion, etc.
sources that contribute to persistent congestion is important to
safe operation of network infrastructure, and mechanisms can The ability to identify sources that contribute to persistent
inform configuration of network devices to complement the endpoint congestion is important to safe operation of network
congestion avoidance mechanisms [RFC7567] [RFC8084] to avoid a infrastructure, and mechanisms can inform configuration of network
portion of the network being driven into congestion collapse devices to complement the endpoint congestion avoidance mechanisms
[RFC2914]. [RFC7567] [RFC8084] to avoid a portion of the network being driven
into congestion collapse [RFC2914].
Congestion Control Compliance for UDP traffic: UDP provides a Congestion Control Compliance for UDP traffic: UDP provides a
minimal message-passing datagram transport that has no inherent minimal message-passing datagram transport that has no inherent
congestion control mechanisms. Because congestion control is congestion control mechanisms. Because congestion control is
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 are required other protocols that choose to use UDP as a transport are required
to employ mechanisms to prevent congestion collapse, avoid to employ mechanisms to prevent congestion collapse, avoid
unacceptable contributions to jitter/latency, and to establish an unacceptable contributions to jitter/latency, and to establish an
acceptable share of capacity with concurrent traffic [RFC8085]. acceptable share of capacity with concurrent traffic [RFC8085].
A network operator needs tools to understand if datagram flows A network operator needs tools to understand if datagram flows
comply with congestion control expectations and therefore whether (e.g., using UDP) comply with congestion control expectations and
there is a need to deploy methods such as rate-limiters, transport therefore whether there is a need to deploy methods such as rate-
circuit breakers or other methods to enforce acceptable usage for limiters, transport circuit breakers, or other methods to enforce
the offered service. acceptable usage for the offered service.
UDP flows that expose a well-known header by specifying the format UDP flows that expose a well-known header by specifying the format
of header fields can allow information to be observed to gain of header fields can allow information to 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
the RTP and RTCP header information of real-time flows (see RTP and RTCP header information for real-time flows (see
Section 3.1.2, and the Secure RTP extensions [RFC3711] were Section 3.1.2). The Secure RTP extensions [RFC3711] were
explicitly designed to expose header information to enable such explicitly designed to expose some header information to enable
observation. such observation, while protecting the payload data.
3.3. Use for Network Diagnostics and Troubleshooting 3.3. Use for Network Diagnostics and Troubleshooting
Transport header information can be useful for a variety of Transport header information can be useful for a variety of
operational tasks [RFC8404]: to diagnose network problems, assess operational tasks [RFC8404]: to diagnose network problems, assess
network provider performance, evaluate equipment/protocol network provider performance, evaluate equipment/protocol
performance, capacity planning, management of security threats performance, capacity planning, management of security threats
(including denial of service), and responding to user performance (including denial of service), and responding to user performance
questions. Sections 3.1.2 and 5 of [RFC8404] provide further questions. Section 3.1.2 and Section 5 of [RFC8404] provide further
examples. These tasks seldom involve the need to determine the examples. These tasks seldom involve the need to determine the
contents of the transport payload, or other application details. contents of the transport payload, or other application details.
A network operator supporting traffic that uses transport header A network operator supporting traffic that uses transport header
encryption can see only encrypted transport headers. This prevents encryption can see only encrypted transport headers. This prevents
deployment of performance measurement tools that rely on transport deployment of performance measurement tools that rely on transport
protocol information. Choosing to encrypt all the information protocol information. Choosing to encrypt all the information
reduces the ability of an operator to observe transport performance reduces the ability of an operator to observe transport performance
and could limit the ability of network operators to trace problems, and could limit the ability of network operators to trace problems,
make appropriate QoS decisions, or response to other queries about make appropriate QoS decisions, or response to other queries about
skipping to change at page 20, line 18 skipping to change at page 20, line 17
an endpoint. 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 from those of wired networks. A radio-based network (e.g., different from 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, with direct impact on the available capacity,
and potentially loss/reordering of packets. The impact of the and potentially loss/reordering of packets. The impact of the
pattern of loss and congestion, differs for different traffic types, pattern of loss and congestion, differs for different traffic types,
correlation with propagation and interference can all have correlation with propagation and interference can all have
significant impact on the cost and performance of a provided service. significant impact on the cost and performance of a provided service.
The need for this type of information is expected to increase as The need for this type of information is expected to increase as
operators bring together heterogeneous types of network equipment and operators bring together heterogeneous types of network equipment and
seek to deploy opportunistic methods to access radio spectrum. seek to deploy opportunistic methods to access radio spectrum.
A flow that conceals its transport header information could imply A flow that conceals its transport header information could imply
"don't touch" to some operators. This could limit a trouble-shooting "don't touch" to some operators. This could limit a trouble-shooting
response to "can't help, no trouble found". response to "can't help, no trouble found".
3.4. Header Compression 3.4. Header Compression
Header compression saves link bandwidth by compressing network and Header compression saves link capacity by compressing network and
transport protocol headers on a per-hop basis. It was widely used transport protocol headers on a per-hop basis. It was widely used
with low bandwidth dial-up access links, and still finds application with low bandwidth dial-up access links, and still finds application
on wireless links that are subject to capacity constraints. Header on wireless links that are subject to capacity constraints. Header
compression has been specified for use with TCP/IP and RTP/UDP/IP compression has been specified for use with TCP/IP and RTP/UDP/IP
flows [RFC2507], [RFC2508], [RFC4995]. flows [RFC2507], [RFC2508], [RFC4995].
While it is possible to compress only the network layer headers, While it is possible to compress only the network layer headers,
significant bandwidth savings can be made if both the network and significant savings can be made if both the network and transport
transport layer headers are compressed together as a single unit. layer headers are compressed together as a single unit. The Secure
The Secure RTP extensions [RFC3711] were explicitly designed to leave RTP extensions [RFC3711] were explicitly designed to leave the
the transport protocol headers unencrypted, but authenticated, since transport protocol headers unencrypted, but authenticated, since
support for header compression was considered important. Encrypting support for header compression was considered important. Encrypting
the transport protocol headers does not break such header the transport protocol headers does not break such header
compression, but does cause it to fall back to compressing only the compression, but does cause it to fall back to compressing only the
network layer headers, with a significant reduction in efficiency. network layer headers, with a significant reduction in efficiency.
This may have operational impact. This can impact the efficiency of a link/path.
4. Encryption and Authentication of Transport Headers 4. Encryption and Authentication of Transport Headers
End-to-end encryption can be applied at various protocol layers. It End-to-end encryption can be applied at various protocol layers. It
can be applied above the transport to encrypt the transport payload. can be applied above the transport to encrypt the transport payload.
Encryption methods can hide information from an eavesdropper in the Encryption methods can hide information from an eavesdropper in the
network. Encryption can also help protect the privacy of a user, by network. Encryption can also help protect the privacy of a user, by
hiding data relating to user/device identity or location. Neither an hiding data relating to user/device identity or location. Neither an
integrity check nor encryption methods prevent traffic analysis, and integrity check nor encryption methods prevent traffic analysis, and
usage needs to reflect that profiling of users, identification of usage needs to reflect that profiling of users, identification of
location and fingerprinting of behaviour can take place even on location and fingerprinting of behaviour can take place even on
encrypted traffic flows. Any header information that has a clear encrypted traffic flows. Any header information that has a clear
definition in the protocol's message format(s), or is implied by that definition in the protocol's message format(s), or is implied by that
definition, and is not cryptographically confidentiality-protected definition, and is not cryptographically confidentiality-protected
can be unambiguously interpreted by on-path observers can be unambiguously interpreted by on-path observers [RFC8546].
[I-D.trammell-wire-image].
There are several motivations: There are several motivations for encryption:
o One motive to use encryption is a response to perceptions that the o One motive to use encryption is a response to perceptions that the
network has become ossified by over-reliance on middleboxes that network has become ossified by over-reliance on middleboxes that
prevent new protocols and mechanisms from being deployed. This prevent new protocols and mechanisms from being deployed. This
has lead to a perception that there is too much "manipulation" of has lead to a perception that there is too much "manipulation" of
protocol headers within the network, and that designing to deploy protocol headers within the network, and that designing to deploy
in such networks is preventing transport evolution. In the light in such networks is preventing transport evolution. In the light
of this, a method that authenticates transport headers may help of this, a method that authenticates transport headers could help
improve the pace of transport development, by eliminating the need improve the pace of transport development, by eliminating the need
to always consider deployed middleboxes to always consider deployed middleboxes
[I-D.trammell-plus-abstract-mech], or potentially to only [I-D.trammell-plus-abstract-mech], or potentially to only
explicitly enable middlebox use for particular paths with explicitly enable use by middleboxes for particular paths with
particular middleboxes that are deliberately deployed to realise a particular middleboxes that are deliberately deployed to realise a
useful function for the network and/or users[RFC3135]. useful function for the network and/or users[RFC3135].
o Another motivation stems from increased concerns about privacy and o Another motivation stems from increased concerns about privacy and
surveillance. Some Internet users have valued the ability to surveillance. Some Internet users have valued the ability to
protect identity, user location, and defend against traffic protect identity, user location, and defend against traffic
analysis, and have used methods such as IPsec Encapsulated analysis, and have used methods such as IPsec Encapsulated
Security Payload (ESP), Virtual Private Networks (VPNs) and other Security Payload (ESP), VPNs and other encrypted tunnel
encrypted tunnel technologies. Revelations about the use of technologies. Revelations about the use of pervasive surveillance
pervasive surveillance [RFC7624] have, to some extent, eroded [RFC7624] have, to some extent, eroded trust in the service
trust in the service offered by network operators, and following offered by network operators, and following the Snowden revelation
the Snowden revelation in the USA in 2013 has led to an increased in the USA in 2013 has led to an increased desire for people to
desire for people to employ encryption to avoid unwanted employ encryption to avoid unwanted "eavesdropping" on their
"eavesdropping" on their communications. Concerns have also been communications. Concerns have also been voiced about the addition
voiced about the addition of information to packets by third of information to packets by third parties to provide analytics,
parties to provide analytics, customization, advertising, cross- customization, advertising, cross-site tracking of users, to bill
site tracking of users, to bill the customer, or to selectively the customer, or to selectively allow or block content. Whatever
allow or block content. Whatever the reasons, there are now the reasons, there are now activities in the IETF to design new
activities in the IETF to design new protocols that could include protocols that could include some form of transport header
some form of transport header encryption (e.g., QUIC encryption (e.g., QUIC [I-D.ietf-quic-transport]) to supplement
[I-D.ietf-quic-transport]). the already widespread payload encryption.
Authentication methods (that provide integrity checks of protocols Authentication methods that provide integrity checks of protocols
fields) have also been specified at the network layer, and this also fields have also been specified at the network layer, and this also
protects transport header fields. The network layer itself carries protects transport header fields. The network layer itself carries
protocol header fields that are increasingly used to help forwarding protocol header fields that are increasingly used to help forwarding
decisions reflect the need of transport protocols, such as the IPv6 decisions reflect the need of transport protocols, such as the IPv6
Flow Label [RFC6437], DSCP, and ECN fields. Flow Label [RFC6437], DSCP, and ECN fields.
The use of transport layer authentication and encryption exposes a The use of transport layer authentication and encryption exposes a
tussle between middlebox vendors, operators, applications developers tussle between middlebox vendors, operators, applications developers
and users. and users:
o On the one hand, future Internet protocols that enable large-scale o On the one hand, future Internet protocols that enable large-scale
encryption assist in the restoration of the end-to-end nature of encryption assist in the restoration of the end-to-end nature of
the Internet by returning complex processing to the endpoints, the Internet by returning complex processing to the endpoints,
since middleboxes cannot modify what they cannot see. since middleboxes cannot modify what they cannot see.
o On the other hand, encryption of transport layer header o On the other hand, encryption of transport layer header
information has implications for people who are responsible for information has implications for people who are responsible for
operating networks and researchers and analysts seeking to operating networks and researchers and analysts seeking to
understand the dynamics of protocols and traffic patterns. understand the dynamics of protocols and traffic patterns.
Whatever the motives, a decision to use pervasive transport header Whatever the motives, a decision to use pervasive transport header
encryption will have implications on the way in which design and encryption will have implications on the way in which design and
evaluation is performed, and which can in turn impact the direction evaluation is performed. This can, in turn, impact the direction of
of evolution of the transport protocol stack. While the IETF can evolution of the transport protocol stack. While the IETF can
specify protocols, the success in actual deployment is often specify protocols, the success in actual deployment is often
determined by many factors [RFC5218] that are not always clear at the determined by many factors [RFC5218] that are not always clear at the
time when protocols are being defined. time when protocols are being defined.
The following briefly reviews some security design options for The following briefly reviews some security design options for
transport protocols. A Survey of Transport Security Protocols transport protocols. A Survey of Transport Security Protocols
[I-D.ietf-taps-transport-security] provides more details concerning [I-D.ietf-taps-transport-security] provides more details concerning
commonly used encryption methods at the transport layer. commonly used encryption methods at the transport layer.
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 integrity check that
protects the immutable transport header fields, but can still protects the immutable transport header fields, but can still
expose the transport protocol header information in the clear, expose the transport protocol header information in the clear,
allowing in-network devices to observe these fields. An integrity allows in-network devices to observe these fields. An integrity
check is not able to prevent in-network modification, but can check is not able to prevent in-network modification, but can
prevent a receiving from accepting changes and avoid impact on the prevent a receiving from accepting changes and avoid impact on the
transport protocol operation. transport protocol operation.
An example transport authentication mechanism is TCP- An example transport authentication mechanism is TCP-
Authentication (TCP-AO) [RFC5925]. This TCP option authenticates Authentication (TCP-AO) [RFC5925]. This TCP option authenticates
the IP pseudo header, TCP header, and TCP data. TCP-AO protects the IP pseudo header, TCP header, and TCP data. TCP-AO protects
the transport layer, preventing attacks from disabling the TCP the transport layer, preventing attacks from disabling the TCP
connection itself and provides replay protection. TCP-AO may connection itself and provides replay protection. TCP-AO may
interact with middleboxes, depending on their behaviour [RFC3234]. 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 in-network modification.
Secure RTP [RFC3711] is another example of a transport protocol Secure RTP [RFC3711] is another example of a transport protocol
that allows header authentication. that allows header authentication.
Greasing: Transport layer header information that is observable can Greasing: Protocols often provide extensibility features, reserving
be observed in the network. Protocols often provide extensibility fields or values for use by future versions of a specification.
features, reserving fields or values for use by future versions of The specification of receivers has traditionally ignored
a specification. The specification of receivers has traditionally unspecified values, however in-network devices have emerged that
ignored unspecified values, however in-network devices have ossify to require a certain value in a field, or re-use a field
emerged that ossify to require a certain value in a field, or re- for another purpose. When the specification is later updated, it
use a 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. This behaviour, presence of observable transport header fields. This behaviour,
known as GREASE (Generate Random Extensions And Sustain known as GREASE (Generate Random Extensions And Sustain
Extensibility), is designed to avoid a network device ossifying Extensibility) is designed to avoid a network device ossifying the
the use of a specific observable field. Greasing seeks to ease use of a specific observable field. Greasing seeks to ease
deployment of new methods. It can also prevent in-network devices deployment of new methods. It can also prevent in-network devices
utilising the information in a transport header, or can make an utilising the information in a transport header, or can make an
observation robust to a set of changing values, rather than a observation robust to a set of changing values, rather than a
specific set of values. specific set of values.
Encrypting the Transport Payload: The transport layer payload can be Encrypting the Transport Payload: The transport layer payload can be
encrypted to protect the content of transport segments. This encrypted to protect the content of transport segments. This
leaves transport protocol header information in the clear. The leaves transport protocol header information in the clear. The
integrity of immutable transport header fields could be protected integrity of immutable transport header fields could be protected
by combining this with an integrity check. by combining this with an integrity check.
Examples of encrypting the payload include Transport Layer Examples of encrypting the payload include Transport Layer
Security (TLS) over TCP [RFC8446] [RFC7525], Datagram TLS (DTLS) Security (TLS) over TCP [RFC8446] [RFC7525], Datagram TLS (DTLS)
over UDP [RFC6347] [RFC7525], Secure RTP [RFC3711], and TCPcrypt over UDP [RFC6347] [RFC7525], Secure RTP [RFC3711], and TCPcrypt
[I-D.ietf-tcpinc-tcpcrypt] which permits opportunistic encryption [RFC8548] which permits opportunistic encryption of the TCP
of the TCP transport payload. transport payload.
Encrypting the Transport Headers and Payload: The network layer Encrypting the Transport Headers and Payload: The network layer
payload could be encrypted (including the entire transport header payload could be encrypted (including the entire transport header
and the payload). This method provides confidentiality of the and the payload). This method provides confidentiality of the
entire transport packet. It therefore does not expose any entire transport packet. It therefore does not expose any
transport information to devices in the network, which also transport information to devices in the network, which also
prevents modification along a network path. prevents modification along a network path.
One example of encryption at the network layer is use of IPsec One example of encryption at the network layer is the use of IPsec
Encapsulating Security Payload (ESP) [RFC4303] in tunnel mode. Encapsulating Security Payload (ESP) [RFC4303] in tunnel mode.
This encrypts and authenticates all transport headers, preventing This encrypts and authenticates all transport headers, preventing
visibility of the transport headers by in-network devices. Some visibility of the transport headers by in-network devices. Some
Virtual Private Network (VPN) methods also encrypt these headers. VPN methods also encrypt these headers.
Selectively Encrypting Transport Headers and Payload: A transport Selectively Encrypting Transport Headers and Payload: A transport
protocol design can encrypt selected header fields, while also protocol design can encrypt selected header fields, while also
choosing to authenticate the entire transport header. This allows choosing to authenticate the entire transport header. This allows
specific transport header fields to be made observable by network specific transport header fields to be made observable by network
devices. End-to end integrity checks can prevent an endpoint from devices. End-to end integrity checks can prevent an endpoint from
undetected modification of the immutable transport headers. undetected modification of the immutable transport headers.
Mutable fields in the transport header provide opportunities for Mutable fields in the transport header provide opportunities for
middleboxes to modify the transport behaviour (e.g., the extended middleboxes to modify the transport behaviour (e.g., the extended
skipping to change at page 24, line 45 skipping to change at page 24, line 44
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
Some measurements can be made by adding additional protocol headers An on-path device can make measurements by appending additional
carrying operations, administration and management (OAM) information protocol headers carrying operations, administration and management
to packets at the ingress to a maintenance domain (e.g., an Ethernet (OAM) information to packets at the ingress to a maintenance domain
protocol header with timestamps and sequence number information using (e.g., an Ethernet protocol header with timestamps and sequence
a method such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data]) number information using a method such as 802.11ag or in-situ OAM
and removing the additional header at the egress of the maintenance [I-D.ietf-ippm-ioam-data]) and removing the additional header at the
domain. This approach enables some types of measurements, but does egress of the maintenance domain. This approach enables some types
not cover the entire range of measurements described in this of measurements, but does not cover the entire range of measurements
document. In some cases, it can be difficult to position measurement described in this document. In some cases, it can be difficult to
tools at the required segments/nodes and there can be challenges in position measurement tools at the required segments/nodes and there
correlating the downsream/upstream information when in-band OAM data can be challenges in correlating the downsream/upstream information
is inserted by an on-path device. This has the advantage that a when in-band OAM data is inserted by an on-path device. This has the
single header can support all transport protocols, but there could advantage that a single header can support all transport protocols,
also be less desirable implications of separating the operation of but there could also be less desirable implications of separating the
the transport protocol from the measurement framework. operation of the transport protocol from the measurement framework.
Another example of a network-layer approach is the IPv6 Performance Another example of a network-layer approach is the IPv6 Performance
and Diagnostic Metrics (PDM) Destination Option [RFC8250]. This and Diagnostic Metrics (PDM) Destination Option [RFC8250]. This
allows a sender to optionally include a destination option that allows a sender to optionally include a destination option that
caries header fields that can be used to observe timestamps and caries header fields that can be used to observe timestamps and
packet sequence numbers. This information could be authenticated by packet sequence numbers. This information could be authenticated by
receiving transport endpoints when the information is added at the receiving transport endpoints when the information is added at the
sender and visible at the receiving endpoint, although methods to do sender and visible at the receiving endpoint, although methods to do
this have not currently been proposed. This method needs to be this have not currently been proposed. This method needs to be
explicitly enabled at the sender. explicitly enabled at the sender.
Current measurements suggest it can be undesirable to rely on methods Current measurement results suggest that it can be undesirable to
requiring the presence of network options or extension headers. IPv4 rely on methods requiring end to end support of network options or
network options are often not supported (or are carried on a slower extension headers across the Internet. IPv4 network options are
processing path) and some IPv6 networks are also known to drop often not supported (or are carried on a slower processing path) and
packets that set an IPv6 header extension (e.g., [RFC7872]). Another some IPv6 networks have been observed to drop packets that set an
disadvantage is that protocols that separately expose header IPv6 header extension (e.g., results from 2016 in [RFC7872]).
information do not necessarily have an incentive to expose the Another possibility is that protocols that separately expose header
information that is utilised by the protocol itself, and could information do not necessarily have an incentive to expose the actual
manipulate the exposed header information to gain an advantage from information that is utilised by the protocol itself and could
the network. therefore manipulate the exposed header information to gain an
advantage from the network. The incentive to reflect actual
transport information needs to be considered when proposing a method
that selectively exposes header information.
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. This approach provides incentives to not reveal any is needed. This approach provides incentives to not reveal any
information that is not necessary for the end-to-end communication. information that is not necessary for the end-to-end communication.
However, there can be performance and operational benefits in However, there can be performance and operational benefits in
exposing selected information to network tools. 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 if the
scientific analysis. Encrypting transport header encryption changes transport community is to maintain an accurate understanding of the
the ability for other actors to collect and independently analyse network. Encrypting transport header encryption changes the ability
data. Internet transport protocols employ a set of mechanisms. Some to collect and independently analyse data. Internet transport
of these need to work in cooperation with the network layer - loss protocols employ a set of mechanisms. Some of these need to work in
detection and recovery, congestion detection and congestion control, cooperation with the network layer for loss detection and recovery,
some of these need to work only end-to-end (e.g., parameter congestion detection and congestion control. Others need to work
negotiation, flow-control). only end-to-end (e.g., parameter negotiation, flow-control).
The majority of present Internet applications use two well-known The majority of present Internet applications use two well-known
transport protocols, TCP and UDP. Although TCP represents the transport protocols, TCP and UDP. Although TCP represents the
majority of current traffic, some real-time applications use UDP, and majority of current traffic, many real-time applications use UDP, and
much of this traffic utilises RTP format headers in the payload of much of this traffic utilises RTP format headers in the payload of
the UDP datagram. Since these protocol headers have been fixed for the UDP datagram. Since these protocol headers have been fixed for
decades, a range of tools and analysis methods have became common and decades, a range of tools and analysis methods have became common and
well-understood. well-understood.
Protocols that expose the state information used by the transport Protocols that expose the state information used by the transport
protocol in their header information (e.g., timestamps used to protocol in their header information (e.g., timestamps used to
calculate the RTT, packet numbers used to asses congestion and 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, since the protocol will not
the observer understands the transport interaction with the network. work otherwise. This increases confidence that the observer
For example, when TCP is used over an unencrypted network path (i.e., understands the transport interaction with the network. For example,
one that does not use IPsec or other encryption below the transport), when TCP is used over an unencrypted network path (i.e., one that
it implicitly exposes header information that can be used for does not use IPsec or other encryption below the transport), it
implicitly exposes header information that can be used for
measurement at any point along the path. This information is measurement at any point along the path. This information is
necessary for the protocol's correct operation, therefore there is no necessary for the protocol's correct operation, therefore there is no
incentive for a TCP implementation to put incorrect information in incentive for a TCP implementation to put incorrect information in
this transport header. A network device can have confidence that the this transport header. A network device can have confidence that the
well-known (and ossified) transport information represents the actual well-known (and ossified) transport information represents the actual
state of the endpoints. state of the endpoints.
When encryption is used to conceal some or all of the transport When encryption is used to conceal some or all of the transport
headers, the transport protocol choose what information to reveal to headers, the transport protocol choose what information to reveal to
the network about its internal state, what information to leave the network about its internal state, what information to leave
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explicitly reveal a session's RTT [I-D.ietf-quic-spin-exp]). explicitly reveal a session's RTT [I-D.ietf-quic-spin-exp]).
When providing or using such information, it becomes important to When providing or using such information, it becomes important to
consider the privacy of the user and their incentive for providing consider the privacy of the user and their incentive for providing
accurate and detailed information. Protocols that selectively reveal accurate and detailed information. Protocols that selectively reveal
some transport state or measurement signals are choosing to establish some transport state or measurement signals are choosing to establish
a trust relationship with the network operators. There is no a trust relationship with the network operators. There is no
protocol mechanism that can guarantee that the information provided protocol mechanism that can guarantee that the information provided
represents the actual transport state of the endpoints, since those represents the actual transport state of the endpoints, since those
endpoints can always send additional information in the encrypted endpoints can always send additional information in the encrypted
part of the header, to update to replace whatever they reveal. This part of the header, to update or replace whatever they reveal. This
reduces the ability to independently measure and verify that a reduces the ability to independently measure and verify that a
protocol is behaving as expected. Some operational uses need the protocol is behaving as expected. Some operational uses need the
information to contain sufficient detail to understand, and possibly information to contain sufficient detail to understand, and possibly
reconstruct, the network traffic pattern for further testing; such reconstruct, the network traffic pattern for further testing; such
operators must gain the trust of transport protocol implementers if operators must gain the trust of transport protocol implementers if
they are to correctly reveal such information. they are to correctly reveal such information.
OAM data records [I-D.ietf-ippm-ioam-data] could be embedded into a OAM data records [I-D.ietf-ippm-ioam-data] could be embedded into a
variety of encapsulation methods at different layers to support the variety of encapsulation methods at different layers to support the
goals of a specific operational domain. OAM-related metadata can goals of a specific operational domain. OAM-related metadata can
support functions such as performance evaluation, path-tracing, path support functions such as performance evaluation, path-tracing, path
verification information, classification and a diversity of other verification information, classification and a diversity of other
uses. When encryption is used to conceal some or all of the uses. When encryption is used to conceal some or all of the
transport headers, analysis will require coordination between actors transport headers, analysis will require coordination between actors
at different layers to successfully characterise flows and correlate at different layers to successfully characterise flows and correlate
the performance or behavior of a specific mechanism with the the performance or behaviour of a specific mechanism with the
configuration and traffic using operational equipment (e.g. configuration and traffic using operational equipment (e.g.,
Combining transport and network measurements to explore congestion combining transport and network measurements to explore congestion
control dynamics or the implications of active queue management). control dynamics, the implications of designs for active queue
management or circuit breakers).
For some usage a standardised endpoint-based logging format (e.g., For some usage a standardised endpoint-based logging format (e.g.,
based onQuic-Trace [Quic-Trace]) could offer an alternative to in- based on Quic-Trace [Quic-Trace]) could offer an alternative for some
network measurement. Such information will have a diversity of uses in-network measurement. Such information will have a diversity of
- examples include developers wishing to debug/understand the uses, including developers wishing to debug/understand the transport/
transport/applictaion protocols with which they work, to researchers application protocols with which they work, researchers seeking to
seeking to spot trends, anomalies and to characterise variants of spot trends and anomalies, and to characterise variants of protocols.
protocols. This use will need to establish the validity and Measurments based on logging will need to establish the validity and
provenance of the logging information (e.g., to establish how and provenance of the logged information to establish how and when traces
when traces were captured). were captured.
However, endpoint logs do not provide equivalent information to in- However, endpoint logs do not provide equivalent information to in-
network measurements. In particular, endpoint logs contain only a network measurements. In particular, endpoint logs contain only a
part of the information needed to understand the operation of network part of the information needed to understand the operation of network
devices and identify issues such as link performance or capacity devices and identify issues such as link performance or capacity
sharing between multiple flows. Additional information is needed to sharing between multiple flows. Additional information is needed to
determine which equipment/links are used and the configuration of determine which equipment/links are used and the configuration of
equipment along the network paths being measured. equipment along the network paths being measured.
6.2. Characterising "Unknown" Network Traffic 6.2. Characterising "Unknown" Network Traffic
skipping to change at page 29, line 23 skipping to change at page 29, line 23
Each change can introduce associated costs, including the cost of Each change can introduce associated costs, including the cost of
collecting data, and the tooling needed to handle multiple formats collecting data, and the tooling needed to handle multiple formats
(possibly as these co-exist in the network, when measurements need to (possibly as these co-exist in the network, when measurements need to
span time periods during which changes are deployed, or to compare span time periods during which changes are deployed, or to compare
with historical data). These costs are incurred by an operator to with historical data). These costs are incurred by an operator to
manage the service and debug network issues. manage the service and debug network issues.
At the time of writing, the additional operational cost of using At the time of writing, the additional operational cost of using
encrypted transports is not yet well understood. Design trade-offs encrypted transports is not yet well understood. Design trade-offs
could mitigate these costs by explicitly choosing to expose selected could mitigate these costs by explicitly choosing to expose selected
information (e.g., header invariants and the spin-bit in information (e.g., header invariants and the spin-bit in QUIC
QUIC[I-D.ietf-quic-transport]), the specification of common log [I-D.ietf-quic-transport]), the specification of common log formats,
formats and development of alternative approaches. and development of alternative approaches.
6.5. Impact on Research, Development and Deployment 6.5. Impact on Research, Development and Deployment
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. Observable transport headers can provide open proceed hand-in-hand. Observable transport headers can provide open
and verifiable measurement data. Observation of pathologies has a and verifiable measurement data. Observation of pathologies has a
critical role in the design of transport protocol mechanisms and critical role in the design of transport protocol mechanisms and
development of new mechanisms and protocols. This helps development of new mechanisms and protocols. This helps
understanding the interactions between cooperating protocols and understanding the interactions between cooperating protocols and
network mechanism, the implications of sharing capacity with other network mechanism, 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 stake holders to review transport header traces helps of other stake holders to review transport header traces helps
develop insight into performance and traffic contribution of specific develop insight into performance and traffic contribution of specific
variants of a protocol. variants of a protocol.
In development of new transport protocol mechanisms, attention needs In development of new transport protocol mechanisms, attention needs
to be paid to the expected scale of deployment. Whatever the to be paid to the expected scale of deployment. Whatever the
mechanism, experience has shown that it is often difficult to mechanism, experience has shown that it is often difficult to
correctly implement combination of mechanisms [RFC8085]. Mechanisms correctly implement combinations of mechanisms [RFC8085]. 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.
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. experiment with and deploy a wide range of protocol mechanisms.
There has been recent interest in a wide range of new transport There has been recent interest in a wide range of new transport
methods, e.g., Larger Initial Window, Proportional Rate Reduction methods, e.g., Larger Initial Window, Proportional Rate Reduction
(PRR), congestion control methods based on measuring bottleneck (PRR), congestion control methods based on measuring bottleneck
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performance data, which in turn demands control over where and when performance data, which in turn demands control over where and when
measurement samples are collected. This requires consideration of measurement samples are collected. This requires consideration of
the methods used to observe data and the appropriate balance between the methods used to observe data and the appropriate balance between
encrypting all and no transport information. encrypting all and no transport information.
7. Conclusions 7. Conclusions
Confidentiality and strong integrity checks have properties that are Confidentiality and strong integrity checks have properties that are
being incorporated into new protocols and that have important being incorporated into new protocols and that have important
benefits. The pace of development of transports using the WebRTC benefits. The pace of development of transports using the WebRTC
data channel and the rapid deployment of the QUIC transport protocol data channel, and the rapid deployment of the QUIC transport
can both be attributed to using the combination of UDP as a substrate protocol, can both be attributed to using the combination of UDP as a
while providing confidentiality and authentication of the substrate while providing confidentiality and authentication of the
encapsulated transport headers and payload. encapsulated transport headers and payload.
To achieve stable Internet operations, the IETF transport community
has, to date, relied heavily on measurement and insights of the
network operations community to understand the trade-offs, and to
inform selection of appropriate mechanisms, to ensure a safe,
reliable, and robust Internet (e.g., [RFC1273],[RFC2914]).
The traffic that can be observed by on-path network devices is a The traffic that can be observed by on-path network devices is a
function of transport protocol design/options, network use, function of transport protocol design/options, network use,
applications, and user characteristics. In general, when only a applications, and user characteristics. In general, when only a
small proportion of the traffic has a specific (different) small proportion of the traffic has a specific (different)
characteristic, such traffic seldom leads to operational concern, characteristic, such traffic seldom leads to operational concern,
although the ability to measure and monitor it is less. The desire although the ability to measure and monitor it is less. The desire
to understand the traffic and protocol interactions typically grows to understand the traffic and protocol interactions typically grows
as the proportion of traffic increases in volume. The challenges as the proportion of traffic increases in volume. The challenges
increase when multiple instances of an evolving protocol contribute increase when multiple instances of an evolving protocol contribute
to the traffic that share network capacity. to the traffic that share network capacity.
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 levels (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 change. If the currently deployed tools and to catch-up with the change. If the currently deployed tools and
methods are no longer relevant then it may no longer be possible 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 inappropriately classified and then that avoids traffic being inappropriately classified and then
receiving a default treatment by the network. The flow label and receiving a default treatment by the network. The flow label and
DSCP fields provide examples of how transport information can be made DSCP fields provide examples of how transport information can be made
available for network-layer decisions. Extension headers could also available for network-layer decisions. Extension headers could also
be used to carry transport information that can inform network-layer be used to carry transport information that can inform network-layer
decisions. Other information may also be useful to various decisions. Other information may also be useful to various
stakeholder (as described in earlier sections), however this document stakeholders, however this document does not make recommendations
does not make recommendations about what information should be about what information should be exposed, to whom it should be
exposed, to whom it should be observable, or how this will be observable, or how this will be achieved.
achieved.
To achieve stable Internet operations the IETF transport community
has to date relied heavily on measurement and insights of the network
operations community to understand the trade-offs, and to inform
selection of appropriate mechanisms, to ensure a safe, reliable, and
robust Internet (e.g., [RFC1273],[RFC2914]).
There are trade-offs and implications of increased use of encryption. There are trade-offs and implications of increased use of encryption
Transport protocol designers have often ignored the implications of when designing a protocol. Transport protocol designers have often
whether the information in transport header fields can or will be ignored the implications of whether the information in transport
used by in-network devices, and the implications this places on header fields can or will be used by in-network devices, and the
protocol evolution. This motivates a design that provides implications this places on protocol evolution. This motivates a
confidentiality of the header information. It can be expected that a design that provides confidentiality of header information. This
lack of visibility of transport header information can impact the lack of visibility of transport header information can be expected to
ways that protocols are deployed, standardised, and their operational impact the ways that protocols are deployed, standardised, and their
support. The impact of hiding transport headers therefore needs to operational support. The impact of hiding transport headers
be considered in the specification and development of protocols and therefore needs to be considered in the specification and development
standards. This has a potential impact on the way in which the IRTF of protocols and standards. This has a potential impact on the way
and IETF develop new protocols, specifications, and guidelines: in which the IRTF and IETF develop new protocols, specifications, and
guidelines:
o Coexistence of Transport and Network Device Protocols/ o Coexistence of Transport and Network Device Protocols/
Configuration: Transmission Control Protocol (TCP) is currently Configuration: Transmission Control Protocol (TCP) is currently
the predominant transport protocol used over Internet paths. Its the predominant transport protocol used over Internet paths. Its
many variants have broadly consistent approaches to avoiding many variants have broadly consistent approaches to avoiding
congestion collapse, and to ensuring the stability of the congestion collapse, and to ensuring the stability of the
Internet. Increased use of transport layer encryption can Internet. Increased use of transport layer encryption can
overcome ossification, allowing deployment of new transports and overcome ossification, allowing deployment of new transports and
different types of congestion control. This flexibility can be different types of congestion control. This flexibility can be
beneficial, but it can come at the cost of fragmenting the beneficial, but it could come at the cost of fragmenting the
ecosystem. There is little doubt that developers will try to ecosystem. There is little doubt that developers will try to
produce high quality transports for their intended target uses, produce high quality transports for their intended target uses,
but it is not yet clear there are sufficient incentives to ensure but it is not yet clear there are sufficient incentives to ensure
good practice that benefits the wide diversity of requirements for good practice that benefits the wide diversity of requirements for
the Internet community as a whole. the Internet community as a whole.
o Supporting Common Specifications: Common open specifications can o Supporting Common Specifications: Common open specifications can
stimulate engagement by developers, users, and researchers. stimulate engagement by developers, users, and researchers.
Increased diversity, and the ability to innovate without public Increased diversity, and the ability to innovate without public
scrutiny, risks point solutions that optimise for specific needs, scrutiny, risks point solutions that optimise for specific needs,
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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
this information is observed. New approaches need to be this information is observed. New approaches need to be
developed. developed.
o Operational Practice: The network operations community relies on o Operational Practice: The network operations community relies on
being able to understand the pattern and requirements of traffic being able to understand the pattern and requirements of traffic
passing over the Internet, both in aggregate and at the flow passing over the Internet, both in aggregate and at the flow
level. These operational practices have developed based on the level. These operational practices have developed based on the
information available from unencrypted transport headers. The information available from unencrypted transport headers. The
iETF supports this activity by developing operations and IETF supports this activity by developing operations and
management specifications, interface specifications, and management specifications, interface specifications, and
associated Best Current Practice (BCP) specifications. Concealing associated Best Current Practice (BCP) specifications. Concealing
transport header information impacts current practice and demand transport header information impacts current practice and demand
new specifications. new specifications.
o Research and Development: Concealing transport information can o Research and Development: Concealing transport information can
impede independent research into new mechanisms, measurement of impede independent research into new mechanisms, measurement of
behaviour, and development initiatives. Experience shows that behaviour, and development initiatives. Experience shows that
transport protocols are complicated to design and complex to transport protocols are complicated to design and complex to
deploy, and that individual mechanisms need to be evaluated while deploy, and that individual mechanisms need to be evaluated while
skipping to change at page 33, line 31 skipping to change at page 33, line 31
it could eliminate the independent self-checks to the it could eliminate the independent self-checks to the
standardisation process that have previously been in place from standardisation process that have previously been in place from
research and academic contributors (e.g., the role of the IRTF research and academic contributors (e.g., the role of the IRTF
Internet Congestion Control Research Groups (ICCRG) and research Internet Congestion Control Research Groups (ICCRG) and research
publications in reviewing new transport mechanisms and assessing publications in reviewing new transport mechanisms and assessing
the impact of their experimental deployment). the impact of their experimental deployment).
The choice of whether future transport protocols encrypt their The choice of whether future transport protocols encrypt their
protocol headers needs to be taken based not solely on security and protocol headers needs to be taken based not solely on security and
privacy considerations, but also taking into account the impact on privacy considerations, but also taking into account the impact on
operations, standards, and research. As [RFC7258] notes: "Making operations, standards and research. As [RFC7258] notes: "Making
networks unmanageable to mitigate (pervasive monitoring) is not an networks unmanageable to mitigate (pervasive monitoring) is not an
acceptable outcome, but ignoring (pervasive monitoring) would go acceptable outcome, but ignoring (pervasive monitoring) would go
against the consensus documented here." against the consensus documented here."
As part of a protocol's design, the community therefore needs to As part of a protocol's design, the community therefore needs to
weigh the benefits of ossifying common headers versus the potential weigh the benefits of ossifying common headers versus the potential
demerits of exposing specific information that could be observed demerits of exposing specific information that could be observed
along the network path, to ensure network operators, researchers and along the network path, to ensure network operators, researchers and
other stakeholders have appropriate tools to manage their networks other stakeholders have appropriate tools to manage their networks
and enable stable operation of the Internet as new protocols are and enable stable operation of the Internet as new protocols are
deployed. An appropriate balance will emerge over time as real deployed. An appropriate balance will emerge over time as real
instances of this tension are considered [RFC7258]. This balance instances of this tension are analysed [RFC7258]. This balance
between information exposed and information concealed ought to be between information exposed and information concealed ought to be
carefully considered when specifying new transport protocols. carefully considered when specifying new transport protocols.
8. Security Considerations 8. Security Considerations
This document is about design and deployment considerations for This document is about design and deployment considerations for
transport protocols. Issues relating to security are discussed in transport protocols. Issues relating to security are discussed
the various sections of the 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 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 design 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
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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 knowledge of the header field. This prevents an on-path device from knowledge of the header field.
It therefore prevents mechanisms being built that directly rely on It therefore prevents mechanisms being built that directly rely on
the information or seeks to infer semantics of an exposed header the information or seeks to infer semantics of an exposed header
field. Hiding headers can limit the ability to measure and field. Hiding headers can limit the ability to measure and
characterise traffic. characterise traffic.
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. This can be used information to detect anomalies in network traffic. This can be used
as the first line of defence yo identify potential threats from DOS as the first line of defence to identify potential threats from DOS
or malware and redirect suspect traffic to dedicated nodes or malware and redirect suspect traffic to dedicated nodes
responsible for DOS analysis, malware detection, or to perform packet responsible for DOS analysis, malware detection, or to perform packet
"scrubbing" (the normalization of packets so that there are no "scrubbing" (the normalization of packets so that there are no
ambiguities in interpretation by the ultimate destination of the ambiguities in interpretation by the ultimate destination of the
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 are sometimes also utilised as a part Exposed transport header fields are sometimes also utilised as a part
of the information used by the receiver of a transport protocol to of the information used by the receiver of a transport protocol to
protect the transport layer from data injection by an attacker. In protect the transport layer from data injection by an attacker. In
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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 obfuscate 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 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 on-path attacks. visible to an attacker). This would also mitigate against on-path
An additional processing cost can be incurred when decryption needs attacks. An additional processing cost can be incurred when
to be attempted before a receiver is able to discard injected decryption needs to be attempted before a receiver is able to discard
packets. injected packets.
Open standards motivate a desire for this evaluation to include Open standards motivate a desire for this evaluation to include
independent observation and evaluation of performance data, which in independent observation and evaluation of performance data, which in
turn suggests control over where and when measurement samples are turn suggests control over where and when measurement samples are
collected. This requires consideration of the appropriate balance collected. This requires consideration of the appropriate balance
between encrypting all and no transport information. Open data, and between encrypting all and no transport information. Open data, and
accessibility to tools that can help understand trends in application accessibility to tools that can help understand trends in application
deployment, network traffic and usage patterns can all contribute to deployment, network traffic and usage patterns can all contribute to
understanding security challenges. understanding security challenges.
skipping to change at page 36, line 6 skipping to change at page 36, line 6
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, Chris Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, Chris
Wood, Thomas Fossati, and other members of the TSVWG for their Wood, Thomas Fossati, and other members of the TSVWG for their
comments and feedback. 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,
opinions expressed and arguments employed reflect only the authors' and the EU Stand ICT Call 4. The opinions expressed and arguments
view. The European Commission is not responsible for any use that employed reflect only the authors' view. The European Commission is
may be made of that information. not responsible for any use that 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.
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-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-06 (work in progress), July 2019.
[I-D.ietf-quic-spin-exp] [I-D.ietf-quic-spin-exp]
Trammell, B. and M. Kuehlewind, "The QUIC Latency Spin Trammell, B. and M. Kuehlewind, "The QUIC Latency Spin
Bit", draft-ietf-quic-spin-exp-01 (work in progress), Bit", draft-ietf-quic-spin-exp-01 (work in progress),
October 2018. 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-22 (work
in progress), August 2018. in progress), July 2019.
[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.
[I-D.ietf-taps-transport-security] [I-D.ietf-taps-transport-security]
Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey Wood, C., Enghardt, T., Pauly, T., Perkins, C., and K.
of Transport Security Protocols", draft-ietf-taps- Rose, "A Survey of Transport Security Protocols", draft-
transport-security-02 (work in progress), June 2018. ietf-taps-transport-security-08 (work in progress), August
2019.
[I-D.ietf-tcpinc-tcpcrypt] [I-D.ietf-tls-grease]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack, Benjamin, D., "Applying GREASE to TLS Extensibility",
Q., and E. Smith, "Cryptographic protection of TCP Streams draft-ietf-tls-grease-04 (work in progress), August 2019.
(tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-12 (work in
progress), June 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]
Thomson, M., "More Apparent Randomization for QUIC",
draft-thomson-quic-grease-00 (work in progress), December
2017.
[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.
[I-D.trammell-wire-image]
Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", draft-trammell-wire-image-04 (work in
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] [Quic-Trace]
"https:QUIC trace utilities //github.com/google/quic- "https:QUIC trace utilities //github.com/google/quic-
skipping to change at page 43, line 5 skipping to change at page 42, line 30
[RFC8404] Moriarty, K., Ed. and A. Morton, Ed., "Effects of [RFC8404] Moriarty, K., Ed. and A. Morton, Ed., "Effects of
Pervasive Encryption on Operators", RFC 8404, Pervasive Encryption on Operators", RFC 8404,
DOI 10.17487/RFC8404, July 2018, DOI 10.17487/RFC8404, July 2018,
<https://www.rfc-editor.org/info/rfc8404>. <https://www.rfc-editor.org/info/rfc8404>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
2019, <https://www.rfc-editor.org/info/rfc8546>.
[RFC8548] Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic Protection of TCP Streams
(tcpcrypt)", RFC 8548, DOI 10.17487/RFC8548, May 2019,
<https://www.rfc-editor.org/info/rfc8548>.
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.
-01 This draft was a result of walking away from the text for a few -01 This draft was a result of walking away from the text for a few
days and then reorganising the content. days and then reorganising the content.
-02 This draft fixes textual errors. -02 This draft fixes textual errors.
-03 This draft follows feedback from people reading this draft. -03 This draft follows feedback from people reading this draft.
skipping to change at page 44, line 37 skipping to change at page 44, line 37
-07 Addressed feedback from Ruediger and Thomas. -07 Addressed feedback from Ruediger and Thomas.
Section 2 deserved some work to make it easier to read and avoid Section 2 deserved some work to make it easier to read and avoid
repetition. This edit finally gets to this, and eliminates some repetition. This edit finally gets to this, and eliminates some
duplication. This also moves some of the material from section 2 to duplication. This also moves some of the material from section 2 to
reform a clearer conclusion. The scope remains focussed on the usage reform a clearer conclusion. The scope remains focussed on the usage
of transport headers and the implications of encryption - not on of transport headers and the implications of encryption - not on
proposals for new techniques/specifications to be developed. proposals for new techniques/specifications to be developed.
-08 Addressed feedback and completed editorial work, including
updating the text referring to RFC7872, in preparation for a WGLC.
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. 114 change blocks. 
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