draft-ietf-tsvwg-transport-encrypt-12.txt   draft-ietf-tsvwg-transport-encrypt-13.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: August 29, 2020 University of Glasgow Expires: September 21, 2020 University of Glasgow
February 26, 2020 March 20, 2020
Considerations around Transport Header Confidentiality, Network Considerations around Transport Header Confidentiality, Network
Operations, and the Evolution of Internet Transport Protocols Operations, and the Evolution of Internet Transport Protocols
draft-ietf-tsvwg-transport-encrypt-12 draft-ietf-tsvwg-transport-encrypt-13
Abstract Abstract
To protect user data and privacy, Internet transport protocols have To protect user data and privacy, Internet transport protocols have
supported payload encryption and authentication for some time. Such supported payload encryption and authentication for some time. Such
encryption and authentication is now also starting to be applied to encryption and authentication is now also starting to be applied to
the transport protocol headers. This helps avoid transport protocol the transport protocol headers. This helps avoid transport protocol
ossification by middleboxes, while also protecting metadata about the ossification by middleboxes, while also protecting metadata about the
communication. Current operational practice in some networks inspect communication. Current operational practice in some networks inspect
transport header information within the network, but this is no transport header information within the network, but this is no
longer possible when those transport headers are encrypted. This longer possible when those transport headers are encrypted. This
document discusses the possible impact when network traffic uses a document discusses the possible impact when network traffic uses a
protocol with an encrypted transport header. It suggests issues to protocol with an encrypted transport header. It suggests issues to
consider when designing new transport protocols, to account for consider when designing new transport protocols or features. These
network operations, prevent network ossification, enable transport considerations arise from concerns such as network operations,
evolution, and respect user privacy. prevention of network ossification, enabling transport protocol
evolution and respect for user privacy.
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.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 29, 2020. This Internet-Draft will expire on September 21, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 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 2, line 29 skipping to change at page 2, line 29
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 4 2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 4
2.1. Use of Transport Header Information in the Network . . . 6 2.1. Use of Transport Header Information in the Network . . . 6
2.2. Authentication of Transport Header Information . . . . . 7 2.2. Authentication of Transport Header Information . . . . . 7
2.3. Perspectives on Observable Transport Header Fields . . . 8 2.3. Perspectives on Observable Transport Header Fields . . . 8
3. Current uses of Transport Headers within the Network . . . . 11 3. Current uses of Transport Headers within the Network . . . . 11
3.1. Observing Transport Information in the Network . . . . . 12 3.1. Observing Transport Information in the Network . . . . . 12
3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 19 3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 20
3.3. Use for Network Diagnostics and Troubleshooting . . . . . 22 3.3. Use for Network Diagnostics and Troubleshooting . . . . . 23
3.4. Header Compression . . . . . . . . . . . . . . . . . . . 24 3.4. Header Compression . . . . . . . . . . . . . . . . . . . 24
4. Encryption and Authentication of Transport Headers . . . . . 24 4. Encryption and Authentication of Transport Headers . . . . . 25
4.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 24 4.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 25
4.2. Approaches to Transport Header Protection . . . . . . . . 25 4.2. Approaches to Transport Header Protection . . . . . . . . 26
5. Addition of Transport Information to Network-Layer Headers . 27 5. Addition of Transport Information to Network-Layer Headers . 28
5.1. Use of OAM within a Maintenance Domain . . . . . . . . . 27 5.1. Use of OAM within a Maintenance Domain . . . . . . . . . 28
5.2. Use of OAM across Multiple Maintenance Domains . . . . . 27 5.2. Use of OAM across Multiple Maintenance Domains . . . . . 28
6. Implications of Protecting the Transport Headers . . . . . . 28 5.3. Exposing Transport Information at the Network Layer . . . 29
6.1. Independent Measurement . . . . . . . . . . . . . . . . . 29 6. Implications of Protecting the Transport Headers . . . . . . 30
6.2. Characterising "Unknown" Network Traffic . . . . . . . . 31 6.1. Independent Measurement . . . . . . . . . . . . . . . . . 30
6.3. Accountability and Internet Transport Protocols . . . . . 31 6.2. Characterising "Unknown" Network Traffic . . . . . . . . 32
6.4. Impact on Network Operations . . . . . . . . . . . . . . 32 6.3. Accountability and Internet Transport Protocols . . . . . 32
6.5. Impact on Research, Development and Deployment . . . . . 32 6.4. Impact on Network Operations . . . . . . . . . . . . . . 33
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 34 6.5. Impact on Research, Development and Deployment . . . . . 34
8. Security Considerations . . . . . . . . . . . . . . . . . . . 36 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 35
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 8. Security Considerations . . . . . . . . . . . . . . . . . . . 38
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
11. Informative References . . . . . . . . . . . . . . . . . . . 39 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 40
Appendix A. Revision information . . . . . . . . . . . . . . . . 46 11. Informative References . . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 Appendix A. Revision information . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
1. Introduction 1. Introduction
Transport protocols have supported end-to-end encryption of payload Transport protocols have supported end-to-end encryption of payload
data for many years. Examples include Transport Layer Security (TLS) data for many years. Examples include Transport Layer Security (TLS)
over TCP [RFC8446], Datagram TLS (DTLS) over UDP [RFC6347], Secure over TCP [RFC8446], Datagram TLS (DTLS) over UDP [RFC6347], Secure
RTP [RFC3711], and TCPcrypt [RFC8548] which permits opportunistic RTP [RFC3711], and TCPcrypt [RFC8548] which permits opportunistic
encryption of the TCP transport payload. Some of these also provide encryption of the TCP transport payload. Some of these also provide
integrity protection of all or part of the transport header. integrity protection of all or part of the transport header.
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terms of providing confidentiality and protecting user privacy. The terms of providing confidentiality and protecting user privacy. The
benefits have been widely discussed, for example in [RFC7624]. This benefits have been widely discussed, for example in [RFC7624]. This
document supports and encourages increased use of end-to-end payload document supports and encourages increased use of end-to-end payload
encryption in transport protocols. The implications of protecting encryption in transport protocols. The implications of protecting
the transport payload data are therefore not further discussed in the transport payload data are therefore not further discussed in
this document. this document.
A further level of protection can be achieved by encrypting the A further level of protection can be achieved by encrypting the
entire network layer payload, including both the transport headers entire network layer payload, including both the transport headers
and the transport payload data. This does not expose any transport and the transport payload data. This does not expose any transport
information to devices in the network, and therefore also prevents header information to devices in the network, and therefore also
modification along a network path. An example of encryption at the prevents modification along a network path. An example of encryption
network layer is the IPsec Encapsulating Security Payload (ESP) at the network layer is the IPsec Encapsulating Security Payload
[RFC4303] in tunnel mode. Virtual Private Networks (VPNs) typically (ESP) [RFC4303] in tunnel mode. Virtual Private Networks (VPNs)
also operate in this way. This form of encryption is not further typically also operate in this way. This form of encryption is not
discussed in this document. further discussed in this document.
There is also a middle ground, comprising transport protocols that There is also a middle ground, comprising transport protocols that
encrypt some, or all, of the transport layer header information, in encrypt some, or all, of the transport layer header information, in
addition to encrypting the transport payload data. An example of addition to encrypting the transport payload data. An example of
such a protocol, that is now seeing widespread interest and such a protocol, that is now seeing widespread interest and
deployment, is the QUIC transport protocol [I-D.ietf-quic-transport]. deployment, is the QUIC transport protocol [I-D.ietf-quic-transport].
The encryption and authentication of transport header information can The encryption and authentication of transport header information can
prevent unwanted modification of transport header information by prevent unwanted modification of transport header information by
middleboxes, reducing the risk of protocol ossification. It also network devices, reducing the risk of protocol ossification. It also
reduces the amount of metadata about the progress of the transport reduces the amount of metadata about the progress of the transport
connection that is visible to the network [RFC8558]. connection that is visible to the network [RFC8558]. In this
document, the term "transport header information" is used to describe
transport layer information concerning the operation of the transport
protocol (i.e., information used by the transport protocol that might
be carried in a protocol header). This does not refer to transport
payload data (i.e., information transferred by the transport
service), which itself could be encrypted.
There is also, however, some impact, in that the widespread use of There is also, however, some impact, in that the widespread use of
transport encryption requires changes to network operations and other transport header encryption requires changes to network operations
practises. Operators could choose to do nothing special with and other practises. Operators could choose to do nothing special
encrypted traffic. In some cases, encryption could drive changes to with encrypted traffic. In some cases, encryption could drive
the design of network measurement for research, operational, and changes to the design of network measurement for research,
standardisation purposes. operational, and standardisation purposes.
The direction in which the use of transport header confidentiality The direction in which the use of transport header encryption evolves
evolves could have significant implications on the way the Internet could have significant implications on the way the Internet
architecture develops, and therefore needs to be considered as a part architecture develops, and therefore needs to be considered as a part
of protocol design. This include considering whether the endpoints of protocol design and evolution. This include considering whether
permit network devices to observe a specific field of the transport the endpoints permit (or are able to permit) network devices to
header; whether the devices could modify that field; and whether any observe a specific information by explicitly exposing a transport
modification can be detected by the receiving endpoint. header field (or a field derived from transport header information)
to the network; whether it is intended that a network device can
modify the field, whether the devices are able to modify that field;
and whether any modification along the network path can be detected
by the receiving endpoint.
As discussed in [RFC7258], the IETF has concluded that Pervasive As discussed in [RFC7258], the IETF has concluded that Pervasive
Monitoring (PM) is a technical attack that needs to be mitigated in Monitoring (PM) is a technical attack that needs to be mitigated in
the design of IETF protocols, but RFC7528 also notes that "Making the design of IETF protocols, but RFC7528 also notes that "Making
networks unmanageable to mitigate PM is not an acceptable outcome, networks unmanageable to mitigate PM is not an acceptable outcome,
but ignoring PM would go against the consensus documented here. An but ignoring PM would go against the consensus documented here. An
appropriate balance will emerge over time as real instances of this appropriate balance will emerge over time as real instances of this
tension are considered". In support of achieving that balance, this tension are considered". In support of achieving that balance, this
document discusses design and deployment considerations for use of document discusses design and deployment considerations for use of
transport header encryption to protect against pervasive monitoring. transport header encryption to protect against pervasive monitoring.
The transport protocols developed for the Internet are used across a The transport protocols developed for the Internet are used across a
wide range of paths across network segments with many different wide range of paths across network segments with many different
regulatory, commercial, and engineering considerations. This regulatory, commercial, and engineering considerations. This
document considers some of the costs and changes to network document considers some of the costs and changes to network
management and research that are implied by widespread use of management and research that are implied by widespread use of
transport protocols that encrypt their transport header information. transport protocols that encrypt their transport header information.
It reviews the implications of developing transport protocols that It reviews the implications of developing transport protocols that
use end-to-end encryption to provide confidentiality of their use end-to-end encryption to provide confidentiality of their
transport layer headers, and considers the effect of such changes on transport layer headers, and considers the effect of such changes on
transport protocol design and network operations. It also considers transport protocol design, transport protocol evolution, and network
some anticipated implications on transport and application evolution. operations. It also considers some anticipated implications on
This provides considerations relating to the design of transport application evolution. This provides considerations relating to the
protocols that protect their header information and respect user design of transport protocols and features where the transport
privacy. protocol encrypts some or all of their header information.
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 over the network-layer service, and are usually sent in the layer over the network-layer service, and are usually sent in the
payload of network-layer packets. They support end-to-end payload of network-layer packets. Transport protocols support end-
communication between applications, using higher-layer protocols to-end communication between applications, using higher-layer
running on the end systems (transport endpoints). protocols running on the end systems (i.e., transport endpoints).
This simple architectural view does not present one of the core This simple architectural view does not present one of the core
functions of an Internet transport: to discover and adapt to the functions of an Internet transport: to discover and adapt to the
network path that is currently being used. The design of Internet characteristics of the network path that is currently being used.
transport protocols is as much about trying to avoid the unwanted The design of Internet transport protocols is as much about trying to
side effects of congestion on a flow and other capacity-sharing avoid the unwanted side effects of congestion on a flow and other
flows, avoiding congestion collapse, adapting to changes in the path capacity-sharing flows, avoiding congestion collapse, adapting to
characteristics, etc., as it is about end-to-end feature negotiation, changes in the path characteristics, etc., as it is about end-to-end
flow control, and optimising for performance of a specific feature negotiation, flow control, and optimising for performance of
application. a specific application.
Transport headers have end-to-end meaning, but have often been Transport headers have end-to-end meaning, but have often been
observed by equipment within the network. Transport protocol observed by equipment within the network. Transport protocol
specifications have not tended to consider this, and have failed to specifications have not tended to consider this, and have often
indicate what parts of the transport header are intended to be failed to indicate what parts of the transport header are intended to
invariant across protocol versions and visible to the network; what be invariant across protocol versions and visible to the network; to
parts of the header can be modified by the network to signal to the specify what parts of the transport header can be modified by the
transport, and in what way; and what parts of the header are private network to signal to the transport, and in what way; and to define
and/or expected to change in future, and need to be protected for which parts of the header are private and/or expected to change in
privacy or to prevent protocol ossification. future and which need to be protected for privacy or to prevent
protocol ossification. This motivates a need to change the way
transport protocols are designed, modified, and specified.
Increasing concern about pervasive network monitoring Increasing concern about pervasive network monitoring
[RFC7258][RFC7624], and growing awareness of the problem of protocol [RFC7258][RFC7624], and growing awareness of the problem of protocol
ossification caused by middlebox interference with Internet traffic, ossification caused by middlebox interference with Internet traffic,
has motivated a shift in transport protocol design. Recent transport has motivated a shift in transport protocol design. Recent transport
protocols, such as QUIC [I-D.ietf-quic-transport], encrypt the protocols, such as QUIC [I-D.ietf-quic-transport], encrypt the
majority of their transport headers to prevent observation and majority of their transport headers to prevent observation and
protect against modification by the network, and to make explicit protect against modification by the network, and to make explicit
their invariants and what is intended to be visible to the network. their invariants and what is intended to be visible to the network.
Transport header encryption is expected to form a core part of future Transport header encryption is expected to form a core part of future
transport protocol designs. It can help to protect against pervasive transport protocol designs. It can help to protect against pervasive
monitoring, improve privacy, and reduce protocol ossification. monitoring, improve privacy, and reduce protocol ossification.
Transport protocols that use header encryption with secure key Transport protocols that use header encryption with secure key
distribution can provide confidentiality and protection for some, or distribution can provide confidentiality and protection for some, or
all, of the transport header information, controlling what is visible all, of the transport header, controlling what is visible to, and can
to, and can be modified by, the network. be modified by, the network.
The increased use of transport header encryption has benefits, but The increased use of transport header encryption has benefits, but
also has implications for the broader ecosystem. The transport also has implications for the broader ecosystem. The transport
community has, to date, relied heavily on measurements and insights community has, to date, relied heavily on measurements and insights
from the network operations community to understand protocol from the network operations community to understand protocol
behaviour, and to inform the selection of appropriate mechanisms to behaviour, and to inform the selection of appropriate mechanisms to
ensure a safe, reliable, and robust Internet. In turn, network ensure a safe, reliable, and robust Internet. In turn, network
operators and access providers have relied upon being able to observe operators and access providers have relied upon being able to observe
traffic patterns and requirements, both in aggregate and at the flow traffic patterns and requirements, both in aggregate and at the flow
level, to help understand and optimise the behaviour of their level, to help understand and optimise the behaviour of their
networks. Transport header encryption can be used to intentionally networks. Transport header encryption can be used to intentionally
limit the information available to network observers. The widespread limit the information available to network observers. The widespread
use of transport header encryption would therefore limit such use of transport header encryption would therefore limit such
observations in future. It is important to understand how transport observations, unless transport protocols are modified to selectively
header information is used in the network, to allow future protocol expose transport header information outside of the encrypted
designs to make an informed choice on what, if any, headers to expose transport header. It is important to understand how transport header
to the network. information is used by networks, to allow future protocol designs to
make an informed choice on what, if any, transport layer information
to expose to the network.
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, control cost and improve service reliability. to enhance performance, control cost and improve service reliability.
To support network operations and enhance performance, some operators To support network operations and enhance performance, some operators
have deployed functionality that utilises on-path observations of the have deployed functionality that utilises on-path observations of the
transport headers of packets passing through their network. transport headers of packets passing through their network.
When network devices rely on the presence of a header field or the When network devices rely on the presence of a header field or the
semantics of specific header information, this can lead to semantics of specific header information, this can lead to
ossification where an endpoint has to supply a specific header to ossification where an endpoint has to supply a specific header to
receive the network service that it desires. receive the network service that it desires.
In some cases, network-layer use of transport header information can In some cases, network-layer use of transport layer information can
be benign or advantageous to the protocol (e.g., recognising the be benign or advantageous to the protocol (e.g., recognising the
start of a TCP connection, providing header compression for a Secure start of a TCP connection, providing header compression for a Secure
RTP flow, or explicitly using exposed protocol information to provide RTP flow, or explicitly using exposed protocol information to provide
consistent decisions by on-path devices). Header compression (e.g., consistent decisions by on-path devices). Header compression (e.g.,
[RFC5795]) depends understanding of transport header and the way [RFC5795]) depends understanding of transport header and the way
fields change packet-by-packet; as also do techniques to improve TCP fields change packet-by-packet; as also do techniques to improve TCP
performance by transparent modification of acknowledgement traffic performance by transparent modification of acknowledgement traffic
[RFC3449]. Introducing a new transport protocol or changes to [RFC3449]. Introducing a new transport protocol or changes to
existing transport header information prevent these methods being existing transport header information prevent these methods being
used or require the network devices to be updated. used or require the network devices to be updated.
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People seeking to understand network traffic could still come to rely People seeking to understand network traffic could still come to rely
on pattern inferences and other heuristics or machine learning to on pattern inferences and other heuristics or machine learning to
derive measurement data and as the basis for network forwarding derive measurement data and as the basis for network forwarding
decisions [RFC8546]. This can also create dependencies on the decisions [RFC8546]. This can also create dependencies on the
transport protocol, or the patterns of traffic it can generate, also transport protocol, or the patterns of traffic it can generate, also
in time resulting in ossification of the service. in time resulting in ossification of the service.
2.2. Authentication of Transport Header Information 2.2. Authentication of Transport Header Information
The designers of a transport protocol decide whether to encrypt all, The designers of a transport protocol decide whether to encrypt all,
or a part of, the transport header information. Section 4 of RFC8558 or a part of, the transport layer information. Section 4 of RFC8558
states: "Anything exposed to the path should be done with the intent states: "Anything exposed to the path should be done with the intent
that it be used by the network elements on the path" [RFC8558]. New that it be used by the network elements on the path" [RFC8558].
protocol designs can decide not to encrypt certain transport header
fields, making those fields observable in the network. Where fields Protocol designs can decide not to encrypt certain transport header
are intended to immutable (i.e., can be observed, but not modified by fields, making those fields observable in the network, or can choose
to expose new fields designed to explicitly expose observable
transport layer information to the network. Where exposed fields are
intended to be immutable (i.e., can be observed, but not modified by
a network device), the endpoints are encouraged to use authentication a network device), the endpoints are encouraged to use authentication
to provide a cryptographic integrity check that includes these to provide a cryptographic integrity check that includes these
immutable fields to detect any manipulation by network devices. immutable fields to detect any manipulation by network devices.
Making part of a transport header observable can lead to ossification Making part of a transport header observable, or exposing new header
of that part of a header, as middleboxes come to rely on observations fields, can lead to ossification of that part of a header as network
of the exposed fields. A protocol design that provides an observable devices come to rely on observations of the exposed fields. A
field might want to avoid inspection restricting the choice of usable protocol design that provides an observable field might want to
values in the field by intentionally varying the format and/or value restrict the choice of usable values in a field by intentionally
of the field to reduce the chance of ossification (see Section 4). varying the format and/or value of the field to reduce the chance of
ossification (see Section 4).
2.3. Perspectives on Observable Transport Header Fields 2.3. Perspectives on Observable Transport Header Fields
Transport headers fields have been observed within the network for a Transport headers fields have been observed within the network for a
variety of purposes. Some of these are related to network management variety of purposes. Some of these are related to network management
and operations. The lists below, and in the following section, seek and operations. The lists below, and in the following section, seek
to identify some of these uses and the implications of the increased to identify some of these uses and the implications of the increased
use of transport header encryption. This analysis does not judge use of transport header encryption. This analysis does not judge
whether specific practises are necessary, or endorse the use of any whether specific practises are necessary, or endorse the use of any
specific approach. specific approach.
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application. application.
When transport header information is not When transport header information is not
observable, it cannot be used by network observable, it cannot be used by network
operators. Some operators might work without operators. Some operators might work without
that information, or some might turn to more that information, or some might turn to more
ambitious ways to collect, estimate, or infer ambitious ways to collect, estimate, or infer
this data. (Operational practises aimed at this data. (Operational practises aimed at
guessing transport parameters are out of scope guessing transport parameters are out of scope
for this document, and are only mentioned here to for this document, and are only mentioned here to
recognize that encryption does not stop operators recognise that encryption does not stop operators
from attempting to apply practises that have been from attempting to apply practises that have been
used with unencrypted transport headers.) used with unencrypted transport headers.)
See also Section 3, Section 5, Section 6.4 and s See also Section 3, Section 5, Section 6.4 and s
(Section 6.5). (Section 6.5).
Analysis of Aggregate Traffic: Observable transport headers have Analysis of Aggregate Traffic: Observable transport headers have
been utilised to determine which transport been utilised to determine which transport
protocols and features are being used across a protocols and features are being used across a
network segment, and to measure trends in the network segment, and to measure trends in the
pattern of usage. For some use cases, end-to-end pattern of usage. For some use cases, end-to-end
measurements/traces are sufficient and can assist measurements/traces are sufficient and can assist
in developing and debugging new transports and in developing and debugging new transports and
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important to relate observations to specific important to relate observations to specific
equipment/configurations or particular network equipment/configurations or particular network
segments. segments.
This information can help anticipate the demand This information can help anticipate the demand
for network upgrades and roll-out, or affect on- for network upgrades and roll-out, or affect on-
going traffic engineering activities performed by going traffic engineering activities performed by
operators such as determining which parts of the operators such as determining which parts of the
path contribute delay, jitter, or loss. path contribute delay, jitter, or loss.
Tools that rely upon observing headers, could Tools that rely upon observing specific headers,
fail to produce useful data when those headers could fail to produce useful data when those
are encrypted. While this impact could, in many headers are encrypted. While this impact could,
cases, be small, there are scenarios where in many cases, be small, there are scenarios
operators have actively monitored and supported where operators have actively monitored and
particular services, e.g., to explore issues supported particular services, e.g., to explore
relating to Quality of Service (QoS), to perform issues relating to Quality of Service (QoS), to
fast re-routing of critical traffic, to mitigate perform fast re-routing of critical traffic, to
the characteristics of specific radio links, and mitigate the characteristics of specific radio
so on. links, and so on.
See also Section 3.1 to Section 3.2 and See also Section 3.1 to Section 3.2 and
Section 5. Section 5.
Troubleshooting: Observable transport headers have been utilised Troubleshooting: Observable transport headers have been utilised
by operators as a part of network troubleshooting by operators as a part of network troubleshooting
and diagnostics. Metrics derived from this and diagnostics. Metrics derived from this
observed header information can help localise the observed header information can help localise the
network segment introducing the loss or latency. network segment introducing the loss or latency.
Effective troubleshooting often requires Effective troubleshooting often requires
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layers to provide these functions. [RFC8558] layers to provide these functions. [RFC8558]
motivates the design of signals to focus on their motivates the design of signals to focus on their
usage, decoupled from the internal design of the usage, decoupled from the internal design of the
protocol state machine. This could avoid protocol state machine. This could avoid
ossifying the protocol around the design of a ossifying the protocol around the design of a
specific protocol mechanism. specific protocol mechanism.
See also Section 3.3 and Section 5. See also Section 3.3 and Section 5.
Network Protection: Observable transport headers currently provide Network Protection: Observable transport headers currently provide
useful input to classify and detect anomalous information that is useful input to classify and
events, such as changes in application behaviour detect anomalous events, such as changes in
or distributed denial of service attacks. application behaviour or distributed denial of
Operators often seek to uniquely disambiguate service attacks. Operators often seek to
unwanted traffic. uniquely disambiguate unwanted traffic.
Where flows cannot be disambiguated based on Where flows cannot be disambiguated based on
transport information, this could result in less- transport header information, this could result
efficient identification of unwanted traffic, the in less-efficient identification of unwanted
introduction of rate limits for uncharacterised traffic, the introduction of rate limits for
traffic, or the use of heuristics to identify uncharacterised traffic, or the use of heuristics
anomalous flows. to identify anomalous flows.
See also Section 6.2 and Section 6.3. See also Section 6.2 and Section 6.3.
Verifiable Data: Observable transport headers can be used to Verifiable Data: Observable transport headers can be used to
provide open and verifiable measurements to provide open and verifiable measurements to
support operations, research, and protocol support operations, research, and protocol
development. The ability of multiple stake development. The ability of multiple stake
holders to review transport header traces helps holders to review transport header traces helps
develop insight into performance and traffic develop insight into performance and traffic
contribution of specific variants of a protocol. contribution of specific variants of a protocol.
Independently observed data is important to help Independently observed data is important to help
ensure the health of the research and development ensure the health of the research and development
communities. communities.
When transport header information can not be When transport header information can not be
observed, this can reduce the range of actors observed, this can reduce the range of actors
that can observe data. This limits the that can observe data. This limits the
information sources available to the Internet information sources available to the Internet
community to understand the operation of new community to understand the operation of
transport protocols, reducing information to transport protocols, reducing information to
inform design decisions and standardisation of inform design decisions and standardisation of
the new protocols and related operational the new protocols/features and related
practises operational practises
See also Section 6. See also Section 6.
SLA Compliance: Observable transport headers coupled with SLA Compliance: Observable transport headers coupled with
published transport specifications allow published transport specifications allow
operators and regulators to explore the operators and regulators to explore the
compliance with Service Level Agreements (SLAs). compliance with Service Level Agreements (SLAs).
When transport header information can not be When transport header information can not be
observed, other methods have to be found to observed, other methods have to be found to
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There are architectural challenges and considerations in the way There 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 [Measurement]. The decision compare different transport solutions [Measurement]. The decision
about which transport headers fields are made observable offers about which transport headers fields are made observable offers
trade-offs around header confidentiality versus header observability trade-offs around header confidentiality versus header observability
(including non-encrypted but authenticated header fields) for network (including non-encrypted but authenticated header fields) for network
operations and management, and the implications for ossification and operations and management, and the implications for ossification and
user privacy. Different parties will view the relative importance of user privacy. Different parties will view the relative importance of
these differently. For some, the benefits of encrypting all these differently. For some, the benefits of encrypting all
transport headers outweigh the impact of doing so; others might transport headers outweigh the impact of doing so; others might
analyse the security, privacy and ossification impacts and arrive at analyse the security, privacy and ossification impacts, and arrive at
a different trade-off. a different trade-off.
To understand the implications, it is necessary to understand how To understand the implications, it is necessary to understand how
transport layer headers are currently observed and/or modified by transport layer headers are currently observed and/or modified by
middleboxes within the network. This section therefore reviews middleboxes within the network. This section therefore reviews
examples of current usage. It does not consider the intentional examples of current usage. It does not consider the intentional
modification of transport headers by middleboxes (such as in Network modification of transport headers by middleboxes (such as in Network
Address Translation, NAT, or Firewalls). Common issues concerning IP Address Translation, NAT, or Firewalls). Common issues concerning IP
address sharing are described in [RFC6269]. address sharing are described in [RFC6269].
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the header, e.g., by defining the wire image [RFC8546]. As the header, e.g., by defining the wire image [RFC8546]. As
protocols evolve over time, new transport headers could be protocols evolve over time, new transport headers could be
introduced. Detecting this could require interpretation of introduced. Detecting this could require interpretation of
protocol version information or connection setup information; protocol version information or connection setup information;
o Observing transport header information depends on the observer o Observing transport header information depends on the observer
knowing the location and the syntax of the observable transport knowing the location and the syntax of the observable transport
headers. IETF transport protocols can specify this information. headers. 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 header information has been utilised.
3.1.1. Flow Identification Using Transport Layer Headers 3.1.1. Flow Identification Using Transport Layer Headers
Flow/Session identification [RFC8558] is a common function. For Flow/Session identification [RFC8558] is a common function. For
example, performed by measurement activities, QoS classification, example, performed by measurement activities, QoS classification,
firewalls, Denial of Service, DOS, prevention. firewalls, Denial of Service, DOS, prevention.
Observable transport header information, together with information in Observable transport header information, together with information in
the network header, has been used to identify flows and their the network header, has been used to identify flows and their
connection state, together with the set of protocol options being connection state, together with the set of protocol options being
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When transport header information can not be observed, this removes When transport header information can not be observed, this removes
information that could have been used to classify flows by passive information that could have been used to classify flows by passive
observers along the path. More ambitious ways could be used to observers along the path. More ambitious ways could be used to
collect, estimate, or infer flow information, including heuristics collect, estimate, or infer flow information, including heuristics
based on the analysis of traffic patterns. For example, an operator based on the analysis of traffic patterns. For example, an operator
that cannot access the Session Description Protocol (SDP) session that cannot access the Session Description Protocol (SDP) session
descriptions to classify a flow as audio traffic, might instead use descriptions to classify a flow as audio traffic, might instead use
(possibly less-reliable) heuristics to infer that short UDP packets (possibly less-reliable) heuristics to infer that short UDP packets
with regular spacing carry audio traffic. Operational practises with regular spacing carry audio traffic. Operational practises
aimed at inferring transport parameters are out of scope for this aimed at inferring transport parameters are out of scope for this
document, and are only mentioned here to recognize that encryption document, and are only mentioned here to recognise that encryption
does not prevent operators from attempting to apply practises that does not prevent operators from attempting to apply practises that
were used with unencrypted transport headers. The IAB have provided were used with unencrypted transport headers. The IAB have provided
a summary of expected implications of increased encryption on network a summary of expected implications of increased encryption on network
functions that use the observable headers [RFC8546] and describe the functions that use the observable headers [RFC8546] and describe the
expected benefits of designs that explicitly declare protocol expected benefits of designs that explicitly declare protocol
invariant header information that can be used for this purpose. invariant header information that can be used for this purpose.
3.1.2. Metrics derived from Transport Layer Headers 3.1.2. Metrics derived from Transport Layer Headers
Observable transport headers enable explicit measurement and analysis Observable transport headers enable explicit measurement and analysis
of protocol performance, network anomalies, and failure pathologies of protocol performance, network anomalies, and failure pathologies
at any point along the Internet path. Some operators use passive at any point along the Internet path. Some operators use passive
monitoring to manage their portion of the Internet by characterizing monitoring to manage their portion of the Internet by characterising
the performance of link/network segments. Inferences from transport the performance of link/network segments. Inferences from transport
headers are used to derive performance metrics. A variety of open headers are used to derive performance metrics. A variety of open
source and commercial tools have been deployed that utilise transport source and commercial tools have been deployed that utilise transport
header information in this way to derive the following metrics: header information in this way to derive the following metrics:
Traffic Rate and Volume: Volume measures per-application can be used Traffic Rate and Volume: Volume measures per-application can be used
to characterise the traffic that uses a network segment or the to characterise the traffic that uses a network segment or the
pattern of network usage. Observing the protocol sequence number pattern of network usage. Observing the protocol sequence number
and packet size offers one way to measure this (e.g., measurements and packet size offers one way to measure this (e.g., measurements
observing counters in periodic reports such as RTCP; or observing counters in periodic reports such as RTCP; or
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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., due to interference on a radio link), buffering loss frames (e.g., due to interference on a radio link), buffering loss
(e.g., overflow due to congestion, Active Queue Management, AQM (e.g., overflow due to congestion, Active Queue Management, AQM
[RFC7567], or inadequate provision following traffic pre-emption), [RFC7567], or inadequate provision following traffic pre-emption),
and policing (traffic management). Understanding flow loss rates and policing (traffic management). Understanding flow loss rates
requires either observing sequence numbers in network or transport requires either observing sequence numbers in network or transport
headers, or maintaining per-flow packet counters (flow headers, or maintaining per-flow packet counters (flow
identification often requires transport header information). Per- identification often requires transport layer information). Per-
hop loss can also sometimes be monitored at the interface level by hop loss can also sometimes be monitored at the interface level by
devices in the network. devices in the network.
Losses can often occur as bursts, randomly-timed events, etc. The Losses can often occur as bursts, randomly-timed events, etc. The
pattern of loss can provide insight into the cause of loss. It pattern of loss can provide insight into the cause of loss. It
can also be valuable to understand the conditions under which loss can also be valuable to understand the conditions under which loss
occurs, which usually requires relating loss to the traffic occurs, which usually requires relating loss to the traffic
flowing on the network node/segment at the time of loss. This can flowing on the network node/segment at the time of loss. This can
also help identify cases where loss could have been wrongly also help identify cases where loss could have been wrongly
identified, or where the transport did not require transmission of identified, or where the transport did not require transmission of
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and retransmission of packets, for example by observing packet and retransmission of packets, for example by observing packet
sequence numbers in the TCP or the Real-time Transport Protocol sequence numbers in the TCP or the Real-time Transport Protocol
(RTP) headers [RFC3550]. (RTP) headers [RFC3550].
Latency: Latency is a key performance metric that impacts Latency: Latency is a key performance metric that impacts
application and user-perceived response times. It often application and user-perceived response times. It often
indirectly impacts throughput and flow completion time. This indirectly impacts throughput and flow completion time. This
determines the reaction time of the transport protocol itself, determines the reaction time of the transport protocol itself,
impacting flow setup, congestion control, loss recovery, and other impacting flow setup, congestion control, loss recovery, and other
transport mechanisms. The observed latency can have many transport mechanisms. The observed latency can have many
components [Latency]. Of these, unnecessary/unwanted queuing in components [Latency]. Of these, unnecessary/unwanted queueing 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 allows measurement of the upstream and downstream RTT, but also allows measurement of the upstream and downstream
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utilise information about traffic volumes or patterns of interaction utilise information about traffic volumes or patterns of interaction
to deduce metrics. to deduce metrics.
An alternative approach is to use in-network techniques to add and An alternative approach is to use in-network techniques to add and
observe packet headers to facilitate measurements while traffic observe packet headers to facilitate measurements while traffic
traverses an operational network. This approach does not require the traverses an operational network. This approach does not require the
cooperation of an endpoint. cooperation of an endpoint.
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 is used by a multi-field Information from the transport header is 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 to implement access rules (see constrained networks, and by firewalls to implement access rules (see
also Section 2.2.2 of [RFC8404]). Network-layer classification also Section 2.2.2 of [RFC8404]). Network-layer classification
methods that rely on a multi-field classifier (e.g., inferring QoS methods that rely on a multi-field classifier (e.g., inferring QoS
from the 5-tuple or choice of application protocol) are incompatible from the 5-tuple or choice of application protocol) are incompatible
with transport protocols that encrypt the transport information. with transport protocols that encrypt the transport header
Traffic that cannot be classified typically receives a default information. Traffic that cannot be classified typically receives a
treatment. default treatment.
Transport information can also be explicitly set in network-layer Transport layer information can also be explicitly carried in
header fields that are not encrypted, serving as a replacement/ network-layer header fields that are not encrypted, serving as a
addition to the exposed transport information [RFC8558]. This replacement/addition to the exposed transport header information
information can enable a different forwarding treatment by the [RFC8558]. This information can enable a different forwarding
network, even when a transport employs encryption to protect other treatment by the network, even when a transport employs encryption to
header information. protect other header information.
The user of a transport that multiplexes multiple sub-flows might The user of a transport that multiplexes multiple sub-flows might
want to obscure the presence and characteristics of these sub-flows. want to obscure the presence and characteristics of these sub-flows.
On the other hand, an encrypted transport could set the network-layer On the other hand, an encrypted transport could set the network-layer
information to indicate the presence of sub-flows, and to reflect the information to indicate the presence of sub-flows, and to reflect the
service requirements of individual sub-flows. There are several ways service requirements of individual sub-flows. There are several ways
this could be done: this could be done:
IP Address: Applications normally expose the addresses used by IP Address: Applications normally expose the addresses used by
endpoints, and this is used in the forwarding decisions in network endpoints, and this is used in the forwarding decisions in network
devices. Address and other protocol information can be used by a devices. Address and other protocol information can be used by a
Multi-Field (MF) classifier to determine how traffic is treated Multi-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], ,
[RFC6438]) encourage endpoints to set the IPv6 Flow label field of [RFC6437][RFC6438]) encourage endpoints to set the IPv6 Flow label
the network-layer header. IPv6 "source nodes SHOULD assign each field of the network-layer header. IPv6 "source nodes SHOULD
unrelated transport connection and application data stream to a assign each unrelated transport connection and application data
new flow" [RFC6437]. A multiplexing transport could choose to use stream to a new flow" [RFC6437]. A multiplexing transport could
multiple Flow labels to allow the network to independently forward choose to use multiple Flow labels to allow the network to
sub-flows. RFC6437 provides further guidance on choosing a flow independently forward sub-flows. RFC6437 provides further
label value, stating these "should be chosen such that their bits guidance on choosing a flow label value, stating these "should be
exhibit a high degree of variability", and chosen so that "third chosen such that their bits exhibit a high degree of variability",
parties should be unlikely to be able to guess the next value that and chosen so that "third parties should be unlikely to be able to
a source of flow labels will choose". guess the next value that a source of flow labels will choose".
Once set, a flow label can provide information that can help Once set, a flow label can provide information that can help
inform network-layer queuing and forwarding [RFC6438], for example inform network-layer queueing and forwarding [RFC6438], for
with Equal Cost Multi-Path routing and Link Aggregation [RFC6294]. example with Equal Cost Multi-Path routing and Link Aggregation
Considerations when using IPsec are further described in [RFC6294]. Considerations when using IPsec are further described
[RFC6438]. in [RFC6438].
The choice of how to assign a Flow Label needs to avoid The choice of how to assign a Flow Label needs to avoid
introducing linkability that a network device could observe. introducing linkability that a network device could observe.
Inappropriate use by the transport can have privacy implications Inappropriate use by the transport can have privacy implications
(e.g., assigning the same label to two independent flows that (e.g., assigning the same label to two independent flows that
ought not to be classified the same). ought not to be classified the same).
Using the Network-Layer Differentiated Services Code Point: Using the Network-Layer Differentiated Services Code Point:
Applications can expose their delivery expectations to the network Applications can expose their delivery expectations to 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 queueing and forwarding, rather than an
operator inferring traffic requirements from transport and operator inferring traffic requirements from transport and
application headers via a multi-field classifier. Inappropriate application headers via a multi-field classifier. Inappropriate
use by the transport can have privacy implications (e.g., use by the transport can have privacy implications (e.g.,
assigning a different DSCP to a subflow could assist in a network assigning a different DSCP to a subflow could assist in a network
device discovering the traffic pattern used by an application, device discovering the traffic pattern used by an application,
assigning the same label to two independent flows that ought not assigning the same label to two independent flows that ought not
to be classified the same). The field is mutable, i.e., some to be classified the same). The field is mutable, i.e., some
network devices can be expected to change this field (use of each network devices can be expected to change this field (use of each
DSCP value is defined by an RFC). DSCP value is defined by an RFC).
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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 have to be available to network operators and Tools therefore have 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].
Network-Layer Options Network protocols can carry optional headers.
These can be used to explicitly expose transport header
information to on-path devices operating at the network layer (as
discussed further inSection 5).
IPv4 [RFC0791] has provision for optional header fields identified
by an option type field. IP routers can examine these headers and
are required to ignore IPv4 options that they does not recognise.
Many current paths include network devices that forward packets
that carry options on a slower processing path. Some network
devices (e.g., firewalls) can be (and are) configured to drop
these packets [RFC7126]. RFC 7126 provides Best Current Practice
guidance on how operators should treat IPv4 packets that specify
options.
IPv6 can encode optional network-layer information in separate
headers that may be placed between the IPv6 header and the upper-
layer header [RFC8200]. The Hop-by-Hop Options header, when
present, immediately follows the IPv6 header. IPv6 permits this
header to be examined by any node along the path. While [RFC7872]
required all nodes to examine and process the Hop-by-Hop Options
header, it is now expected [RFC8200] that nodes along a path only
examine and process the Hop-by-Hop Options header if explicitly
configured to do so.
When transport headers cannot be observed, operators are unable to When transport headers cannot be observed, operators are unable to
use this information directly. Careful use of the network layer use this information directly. Careful use of the network layer
features can help provide similar information in the case where the features can help provide similar information in the case where the
network is unable to inspect transport protocol headers. Section 5 network is unable to inspect transport protocol headers. Section 5
describes use of network extension headers. describes use of network extension headers.
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
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Traffic rate and volume measurements are used by operators to help Traffic rate and volume measurements are used by operators to help
plan deployment of new equipment and configuration in their networks. plan deployment of new equipment and configuration in their networks.
Data is also valuable to equipment vendors who want to understand Data is also valuable to equipment vendors who want to understand
traffic trends and patterns of usage as inputs to decisions about traffic trends and patterns of usage as inputs to decisions about
planning products and provisioning for new deployments. This planning products and provisioning for new deployments. This
measurement information can also be correlated with billing measurement information can also be correlated with billing
information when this is also collected by an operator. information when this is also collected by an operator.
Trends in aggregate traffic can be observed and can be related to the Trends in aggregate traffic can be observed and can be related to the
endpoint addresses being used, but when transport information is not endpoint addresses being used, but when transport header information
observable, it might be impossible to correlate patterns in is not observable, it might be impossible to correlate patterns in
measurements with changes in transport protocols. This increases the measurements with changes in transport protocols. This increases the
dependency on other indirect sources of information to inform dependency on other indirect sources of information to inform
planning and provisioning. planning and provisioning.
3.2.3. Service Performance Measurement 3.2.3. Service Performance Measurement
Performance measurements (e.g., throughput, loss, latency) can be Performance measurements (e.g., throughput, loss, latency) can be
used by various actors to analyse the service offered to the users of used by various actors to analyse the service offered to the users of
a network segment, and to inform operational practice. a network segment, and to inform operational practice.
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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 under persistent congestion, and hence share of the network load under persistent congestion, and hence
to understand whether the behaviour is appropriate for sharing to understand whether the behaviour is appropriate for sharing
limited network capacity. For example, it is common to visualise limited network capacity. For example, it is common to visualise
plots of TCP sequence numbers versus time for a flow to understand plots of TCP sequence numbers versus time for a flow to understand
how a flow shares available capacity, deduce its dynamics in how a flow shares available capacity, deduce its dynamics in
response to congestion, etc. response to congestion, etc.
The ability to identify sources that contribute to persistent The ability to identify sources and flows that contribute to
congestion is important to the safe operation of network persistent congestion is important to the safe operation of
infrastructure, and can inform configuration of network devices to network infrastructure, and can inform configuration of network
complement the endpoint congestion avoidance mechanisms [RFC7567] devices to complement the endpoint congestion avoidance mechanisms
[RFC8084] to avoid a portion of the network being driven into [RFC7567] [RFC8084] to avoid a portion of the network being driven
congestion collapse [RFC2914]. 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 have to other protocols that choose to use UDP as a transport have to
employ mechanisms to prevent collapse, avoid unacceptable employ mechanisms to prevent collapse, avoid unacceptable
contributions to jitter/latency, and to establish an acceptable contributions to jitter/latency, and to establish an acceptable
share of capacity with concurrent traffic [RFC8085]. share of capacity with concurrent traffic [RFC8085].
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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
(e.g., using TLS). This can hide information from an eavesdropper in (e.g., using TLS). This can hide information from an eavesdropper in
the network. It can also help protect the privacy of a user, by the network. It can also help protect the privacy of a user, by
hiding data relating to user/device identity or location. hiding data relating to user/device identity or location.
4.1. Motivation 4.1. Motivation
There are several motivations for encryption: There are several motivations for encryption:
o One motive to encrypt transport headers is in response to o One motive to encrypt transport headers is in response to a
perceptions that the network has become ossified, since traffic growing awareness of the implications of network ossification from
inspecting middleboxes prevent new protocols and mechanisms from network devices that inspect transport headers. Once a network
being deployed. One benefit of encrypting transport headers is devices observes a transport header and becomes reliant upon using
that it can help improve the pace of transport development by it, the overall use of that field can become ossified, preventing
eliminating interference by deployed middleboxes. new protocols and mechanisms from being deployed. One of the
benefits of encrypting transport headers is that it can help
improve the pace of transport development by eliminating
interference by deployed middleboxes.
o Another motivation stems from increased concerns about privacy and o Another motivation stems from increased concerns about privacy and
surveillance. Users value the ability to protect their identity surveillance. Users value the ability to protect their identity
and location, and defend against analysis of the traffic. and location, and defend against analysis of the traffic.
Revelations about the use of pervasive surveillance [RFC7624] Revelations about the use of pervasive surveillance [RFC7624]
have, to some extent, eroded trust in the service offered by have, to some extent, eroded trust in the service offered by
network operators and have led to an increased use of encryption network operators and have led to an increased use of encryption
to avoid unwanted eavesdropping on communications. Concerns have to avoid unwanted eavesdropping on communications. Concerns have
also been voiced about the addition of information to packets by also been voiced about the addition of information to packets by
third parties to provide analytics, customization, advertising, third parties to provide analytics, customisation, advertising,
cross-site tracking of users, to bill the customer, or to cross-site tracking of users, to bill the customer, or to
selectively allow or block content. Whatever the reasons, the selectively allow or block content. Whatever the reasons, the
IETF is designing protocols that include transport header IETF is designing protocols that include transport header
encryption (e.g., QUIC [I-D.ietf-quic-transport]) to supplement encryption (e.g., QUIC [I-D.ietf-quic-transport]) to supplement
the already widespread payload encryption, and to further limit the already widespread payload encryption, and to further limit
exposure of transport metadata to the network. exposure of transport metadata to the network.
The use of transport header authentication and encryption exposes a The use of transport header 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 support transport o On the one hand, future Internet protocols that support transport
header encryption assist in the restoration of the end-to-end header encryption assist in the restoration of the end-to-end
nature of the Internet by returning complex processing to the nature of the Internet by returning complex processing to the
endpoints, since middleboxes cannot modify what they cannot see, endpoints, since middleboxes cannot modify what they cannot see,
and can improve privacy by reducing leakage of transport metadata. and can improve privacy by reducing leakage of transport metadata.
o On the other hand, encryption of transport layer header o On the other hand, encryption of transport layer information has
information has implications for people who are responsible for implications for people who are responsible for operating
operating networks, and researchers and analysts seeking to networks, and researchers and analysts seeking to understand the
understand the dynamics of protocols and traffic patterns. dynamics of protocols and traffic patterns.
A decision to use transport header encryption can improve user A decision to use transport header encryption can improve user
privacy, and can reduce protocol ossification and help the evolution privacy, and can reduce protocol ossification and help the evolution
of the transport protocol stack, but is also has implications for of the transport protocol stack, but is also has implications for
network operations and management. network operations and management.
4.2. Approaches to Transport Header Protection 4.2. Approaches to Transport Header Protection
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
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connection itself and provides replay protection. TCP-AO might connection itself and provides replay protection. TCP-AO might
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: Protocols often provide extensibility features, reserving
fields or values for use by future versions of a specification.
The specification of receivers has traditionally ignored
unspecified values, however in-network devices have emerged that
ossify to require a certain value in a field, or re-use a field
for another purpose. When the specification is later updated, it
is impossible to deploy the new use of the field, and forwarding
of the protocol could even become conditional on a specific header
field value.
A protocol can intentionally vary the value, format, and/or
presence of observable transport header fields. This behaviour,
known as GREASE (Generate Random Extensions And Sustain
Extensibility) is designed to avoid a network device ossifying the
use of a specific observable field. Greasing seeks to ease
deployment of new methods. It can also prevent in-network devices
utilising the information in a transport header, or can make an
observation robust to a set of changing values, rather than a
specific set of values
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 (explicitly exposed either in a transport header field or
undetected modification of the immutable transport headers. lower layer protocol header). A design that only exposes
immutable fields can also perform end-to-end authentication of
these fields across the path to prevent undetected modification of
the immutable transport headers.
Mutable fields in the transport header provide opportunities for Mutable fields in the transport header provide opportunities where
middleboxes to modify the transport behaviour (e.g., the extended network devices can modify the transport behaviour (e.g., the
headers described in [I-D.trammell-plus-abstract-mech]). This extended headers described in [I-D.trammell-plus-abstract-mech]).
considers only immutable fields in the transport headers, that is,
fields that can be authenticated End-to-End across a path.
An example of a method that encrypts some, but not all, transport An example of a method that encrypts some, but not all, transport
information is GRE-in-UDP [RFC8086] when used with GRE encryption. header information is GRE-in-UDP [RFC8086] when used with GRE
encryption.
Optional Encryption of Header Information: There are implications to Optional Encryption of Header Information: There are implications to
the use of optional header encryption in the design of a transport the use of optional header encryption in the design of a transport
protocol, where support of optional mechanisms can increase the protocol, where support of optional mechanisms can increase the
complexity of the protocol and its implementation, and in the complexity of the protocol and its implementation, and in the
management decisions that are have to be made to use variable management decisions that are have to be made to use variable
format fields. Instead, fields of a specific type ought to always format fields. Instead, fields of a specific type ought to always
be sent with the same level of confidentiality or integrity be sent with the same level of confidentiality or integrity
protection. protection.
Greasing: Protocols often provide extensibility features, reserving
fields or values for use by future versions of a specification.
The specification of receivers has traditionally ignored
unspecified values, however in-network devices have emerged that
ossify to require a certain value in a field, or re-use a field
for another purpose. When the specification is later updated, it
is impossible to deploy the new use of the field, and forwarding
of the protocol could even become conditional on a specific header
field value.
A protocol can intentionally vary the value, format, and/or
presence of observable transport header fields. This behaviour,
known as GREASE (Generate Random Extensions And Sustain
Extensibility) is designed to avoid a network device ossifying the
use of a specific observable field. Greasing seeks to ease
deployment of new methods. This seeks to prevent in-network
devices utilising the information in a transport header, or can
make an observation robust to a set of changing values, rather
than a specific set of values. It is not a security mechanism,
although use can be combined with an authentication mechanism.
As seen, different transports use encryption to protect their header As seen, different transports use encryption to protect their header
information to varying degrees. The trend is towards increased information to varying degrees. The trend is towards increased
protection. protection.
5. Addition of Transport Information to Network-Layer Headers 5. Addition of Transport Information to Network-Layer Headers
An on-path device can make measurements by utilising additional An on-path device can make measurements by utilising additional
protocol headers carrying operations, administration and management protocol headers carrying operations, administration and management
(OAM) information in an additional packet header. Using network- (OAM) information in an additional packet header. Using network-
layer approaches to reveal information has the potential that the layer approaches to reveal information has the potential that the
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One example is the IPv6 Performance and Diagnostic Metrics (PDM) One example is the IPv6 Performance and Diagnostic Metrics (PDM)
Destination Option [RFC8250]. This allows a sender to optionally Destination Option [RFC8250]. This allows a sender to optionally
include a destination option that caries header fields that can be include a destination option that caries header fields that can be
used to observe timestamps and packet sequence numbers. This used to observe timestamps and packet sequence numbers. This
information could be authenticated by receiving transport endpoints information could be authenticated by receiving transport endpoints
when the information is added at the sender and visible at the when the information is added at the sender and visible at the
receiving endpoint, although methods to do this have not currently receiving endpoint, although methods to do this have not currently
been proposed. This method has to be explicitly enabled at the been proposed. This method has to be explicitly enabled at the
sender. sender.
Current measurement results suggest that it could currently be 5.3. Exposing Transport Information at the Network Layer
undesirable to rely on methods requiring end-to-end support of
network options or extension headers across the Internet. IPv4
network options are often not supported (or are carried on a slower
processing path) and some IPv6 networks have been observed to drop
packets that set an IPv6 header extension (e.g., results from 2016 in
[RFC7872]).
Protocols can be designed to expose header information separately to Network packets can carry optional headers may be used to explicitly
the (hidden) fields used by the protocol state machine. On the one expose transport header information to the on-path devices operating
hand, such approaches can simplify tools by exposing the relevant at the network layer Section 3.1.3. For example, an endpoint that
metrics (loss, latency, etc), rather having to derive this from other provides an IPv6 Hop-by-Hop option [RFC8200] can provide explicit
fields. This also permits the protocol to evolve independently of transport layer information that can be observed and used by network
the ossified observable header [RFC8558]. On the other hand, devices on the path.
protocols do not necessarily have an incentive to expose the actual
information that is used by the protocol itself and could therefore When the path includes a network device that drops packets that
manipulate the exposed header information to gain an advantage from include a specific option used for this purpose (e.g., see[RFC7872]),
the network. Where the information is provided by an endpoint, the this impacts the proper functioning of the protocols using the path.
incentive to reflect actual transport information has to be Protocol methods can be designed to probe to discover whether the
considered when proposing a method. specific option(s) can be used along the current path, enabling use
on arbitrary paths.
The transport header information exposed by a transport endpoint can
be different to the (hidden) transport header fields used by the
protocol state machine and could instead be specifically designed to
meet the needs of the network layer [RFC8558]. There are
opportunities for the format and usage of this transport information
to be standardised, providing an opportunity for common
specifications and tools to be used with more than one transport
protocol.
o On the one hand, protocols do not necessarily have an incentive to
expose the actual information that is used by the protocol itself
and could therefore manipulate the exposed transport header
information to gain an advantage from the network. The incentive
to reflect actual transport header information has to be
considered when proposing a method.
o On the other hand, explicit approaches can simplify tools by
exposing the relevant metrics (loss, latency, etc), rather having
to derive this from other fields. This could stimulate the
development of proocol-independent tools and also permits
protocols to evolve independently of the ossified observable
header [RFC8558].
6. Implications of Protecting the Transport Headers 6. Implications of Protecting the Transport Headers
The choice of which transport header fields to expose and which to The choice of which transport header fields to expose and which to
encrypt is a design decision for the transport protocol. Selective encrypt is a design decision for the transport protocol. Selective
encryption requires trading conflicting goals of observability and encryption requires trading conflicting goals of observability and
network support, privacy, and risk of ossification, to decide what network support, privacy, and risk of ossification, to decide what
header fields to protect and which to make visible. header fields to protect and which to make visible.
Security work typically employs a design technique that seeks to Security work typically employs a design technique that seeks to
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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, since the protocol will not endpoint to provide correct information, since the protocol will not
work otherwise. This increases confidence that the observer work otherwise. This increases confidence that the observer
understands the transport interaction with the network. For example, understands the transport interaction with the network. For example,
when TCP is used over an unencrypted network path (i.e., one that when TCP is used over an unencrypted network path (i.e., one that
does not use IPsec or other encryption below the transport), it does not use IPsec or other encryption below the transport), it
implicitly exposes header information that can be used for implicitly exposes transport 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 or RTP implementation to put incorrect incentive for a TCP or RTP implementation to put incorrect
information in this transport header. A network device can have information in this transport header. A network device can have
confidence that the well-known (and ossified) transport information confidence that the well-known (and ossified) transport header
represents the actual state of the endpoints. information represents the actual state of the endpoints.
When encryption is used to hide some or all of the transport headers, When encryption is used to hide some or all of the transport headers,
the transport protocol chooses which information to reveal to the the transport protocol chooses which information to reveal to the
network about its internal state, what information to leave network about its internal state, what information to leave
encrypted, and what fields to grease to protect against future encrypted, and what fields to grease to protect against future
ossification. Such a transport could be designed, for example, to ossification. Such a transport could be designed (or an existing
provide summary data regarding its performance, congestion control transport modified), for example, to provide summary data regarding
state, etc., or to make an explicit measurement signal available. its performance, congestion control state, etc., or to make an
For example, a QUIC endpoint can optionally set the spin bit to explicit measurement signal available. For example, a QUIC endpoint
reflect to explicitly reveal the RTT of an encrypted transport can optionally set the spin bit to reflect to explicitly reveal the
session to the on-path network devices [I-D.ietf-quic-transport]). RTT of an encrypted transport session to the on-path network devices
[I-D.ietf-quic-transport]).
When providing or using such information, it is important to consider When providing or using such information, it is important to consider
the privacy of the user and their incentive for providing accurate the privacy of the user and their incentive for providing accurate
and detailed information. Protocols that selectively reveal some and detailed information. Protocols that selectively reveal some
transport state or measurement signals are choosing to establish a transport state or measurement signals are choosing to establish a
trust relationship with the network operators. There is no protocol trust relationship with the network operators. There is no protocol
mechanism that can guarantee that the information provided represents mechanism that can guarantee that the information provided represents
the actual transport state of the endpoints, since those endpoints the actual transport state of the endpoints, since those endpoints
can always send additional information in the encrypted part of the can always send additional information in the encrypted part of the
header, to update or replace whatever they reveal. This reduces the header, to update or replace whatever they reveal. This reduces the
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encryption [RFC5218]. encryption [RFC5218].
6.4. Impact on Network Operations 6.4. Impact on Network Operations
Some network operators currently use observed transport header Some network operators currently use observed transport header
information as a part of their operational practice, and have information as a part of their operational practice, and have
developed tools and techniques that use information observed in developed tools and techniques that use information observed in
currently deployed transports and their applications. A variety of currently deployed transports and their applications. A variety of
open source and proprietary tools have been deployed that use this open source and proprietary tools have been deployed that use this
information for a variety of short and long term measurements. information for a variety of short and long term measurements.
Encryption of the transport information prevents tooling from Encryption of the transport header information prevents tooling from
observing the header information, limiting its utility. directly observing the transport header information, limiting its
utility.
Alternative diagnostic and troubleshooting tools would have to be Alternative diagnostic and troubleshooting tools would have to be
developed and deployed is transport header encryption is widely developed and deployed is transport header encryption is widely
deployed. Introducing a new protocol or application might then deployed. Introducing a new protocol or application might then
require these tool chains and practises to be updated, and could in require these tool chains and practises to be updated, and could in
turn impact operational mechanisms, and policies. Each change can turn impact operational mechanisms, and policies. Each change can
introduce associated costs, including the cost of collecting data, introduce associated costs, including the cost of collecting data,
and the tooling to handle multiple formats (possibly as these co- and the tooling to handle multiple formats (possibly as these co-
exist in the network, when measurements span time periods during exist in the network, when measurements span time periods during
which changes are deployed, or to compare with historical data). which changes are deployed, or to compare with historical data).
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Independently observed data is also important to ensure the health of Independently observed data is also important to ensure the health of
the research and development communities and can help promote the research and development communities and can help promote
acceptance of proposed specifications by the wider community (e.g., acceptance of proposed specifications by the wider community (e.g.,
as a method to judge the safety for Internet deployment) and provides as a method to judge the safety for Internet deployment) and provides
valuable input during standardisation. Open standards motivate a valuable input during standardisation. Open standards motivate a
desire to include independent observation and evaluation of desire to include independent observation and evaluation of
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 header information.
7. Conclusions 7. Conclusions
Header encryption and strong integrity checks are being incorporated Header encryption and strong integrity checks are being incorporated
into new transport protocols and have important benefits. The pace into new transport protocols and have important benefits. The pace
of development of transports using the WebRTC data channel, and the of development of transports using the WebRTC data channel, and the
rapid deployment of the QUIC transport protocol, can both be rapid deployment of the QUIC transport protocol, can both be
attributed to using the combination of UDP as a substrate while attributed to using the combination of UDP as a substrate while
providing confidentiality and authentication of the encapsulated providing confidentiality and authentication of the encapsulated
transport headers and payload. transport headers and payload.
This document has described some current practises, and the This document has described some current practises, and the
implications for some stakeholders, when transport layer header implications for some stake holders, when transport layer header
encryption is used. It does not judge whether these practises are encryption is used. It does not judge whether these practises are
necessary, or endorse the use of any specific practise. Rather, the necessary, or endorse the use of any specific practise. Rather, the
intent is to highlight operational tools and practises to consider intent is to highlight operational tools and practises to consider
when designing transport protocols, so protocol designers can make when designing and modifying transport protocols, so protocol
informed choice about what transport header fields to encrypt, and designers can make informed choice about what transport header fields
whether it might be beneficial to make an explicit choice to expose to encrypt, and whether it might be beneficial to make an explicit
certain fields to the network. In making such a decision, it is choice to expose certain fields to the network. In making such a
important to balance: decision, it is important to balance:
o User Privacy: The less transport header information that is o User Privacy: The less transport header information that is
exposed to the network, the lower the risk of leaking metadata exposed to the network, the lower the risk of leaking metadata
that might have privacy implications for the users. Transports that might have privacy implications for the users. Transports
that chose to expose some header fields need to make a privacy that chose to expose some header fields need to make a privacy
assessment to understand the privacy cost versus benefit trade-off assessment to understand the privacy cost versus benefit trade-off
in making that information available. The process used to define in making that information available. The process used to define
and expose the QUIC spin bit to the network is an example of such and expose the QUIC spin bit to the network is an example of such
an analysis. an analysis.
o Protocol Ossification: Unencrypted transport header fields are o Protocol Ossification: Unencrypted transport header fields are
likely to ossify rapidly, as middleboxes come to rely on their likely to ossify rapidly, as network devices come to rely on their
presence, making it difficult to change the transport in future. presence, making it difficult to change the transport in future.
This argues that the choice to expose information to the network This argues that the choice to expose information to the network
is made deliberately and with care, since it is essentially is made deliberately and with care, since it is essentially
defining a stable interface between the transport and the network. defining a stable interface between the transport and the network.
Some protocols will want to make that interface as limited as Some protocols will want to make that interface as limited as
possible; other protocols might find value in exposing certain possible; other protocols might find value in exposing certain
information to signal to the network, or in allowing the network information to signal to the network, or in allowing the network
to change certain header fields as signals to the transport. The to change certain header fields as signals to the transport. The
visible wire image of a protocol should be explicitly designed. visible wire image of a protocol should be explicitly designed.
o Impact on Operational Practice: The network operations community o Impact on Operational Practice: The network operations community
has long relied on being able to understand Internet traffic has long relied on being able to understand Internet traffic
patterns, both in aggregate and at the flow level, to support patterns, both in aggregate and at the flow level, to support
network management, traffic engineering, and troubleshooting. network management, traffic engineering, and troubleshooting.
Operational practice has developed based on the information Operational practice has developed based on the information
available from unencrypted transport headers. The IETF has available from unencrypted transport headers. The IETF has
supported this practice by developing operations and management supported this practice by developing operations and management
specifications, interface specifications, and associated Best specifications, interface specifications, and associated Best
Current Practises. Widespread deployment of transport protocols Current Practises. Widespread deployment of transport protocols
that encrypt their header information might impact network that encrypt their information might impact network operations,
operations, unless operators can develop alternative practises unless operators can develop alternative practises that work
that work without access to the transport header information. without access to the transport header.
o Pace of Evolution: Removing obstacles to change can enable an o Pace of Evolution: Removing obstacles to change can enable an
increased pace of evolution. If a protocol changes its transport increased pace of evolution. If a protocol changes its transport
header format (wire image) or their transport behaviour, this can header format (wire image) or their transport behaviour, this can
result in the currently deployed tools and methods becoming no result in the currently deployed tools and methods becoming no
longer relevant. Where this needs to be accompanied by longer relevant. Where this needs to be accompanied by
development of appropriate operational support functions and development of appropriate operational support functions and
procedures, it can incur a cost in new tooling to catch-up with procedures, it can incur a cost in new tooling to catch-up with
each change. Protocols that consistently expose observable data each change. Protocols that consistently expose observable data
do not require such development, but can suffer from ossification do not require such development, but can suffer from ossification
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interworking specifications, and on it being possible to detect interworking specifications, and on it being possible to detect
violations. It is important to find new ways of maintaining that violations. It is important to find new ways of maintaining that
community trust as increased use of transport header encryption community trust as increased use of transport header encryption
limits visibility into transport behaviour. limits visibility into transport behaviour.
o Impact on Benchmarking and Understanding Feature Interactions: An o Impact on Benchmarking and Understanding Feature Interactions: An
appropriate vantage point for observation, coupled with timing appropriate vantage point for observation, coupled with timing
information about traffic flows, provides a valuable tool for information about traffic flows, provides a valuable tool for
benchmarking network devices, endpoint stacks, functions, and/or benchmarking network devices, endpoint stacks, functions, and/or
configurations. This can also help with understanding complex configurations. This can also help with understanding complex
feature interactions. An inability to observe transport layer feature interactions. An inability to observe transport header
header information can make it harder to diagnose and explore information can make it harder to diagnose and explore
interactions between features at different protocol layers, a interactions between features at different protocol layers, a
side-effect of not allowing a choice of vantage point from which side-effect of not allowing a choice of vantage point from which
this information is observed. New approaches might have to be this information is observed. New approaches might have to be
developed. developed.
o Impact on Research and Development: Hiding transport information o Impact on Research and Development: Hiding transport header
can impede independent research into new mechanisms, measurement information can impede independent research into new mechanisms,
of behaviour, and development initiatives. Experience shows that measurement of behaviour, and development initiatives. Experience
transport protocols are complicated to design and complex to shows that transport protocols are complicated to design and
deploy, and that individual mechanisms have to be evaluated while complex to deploy, and that individual mechanisms have to be
considering other mechanisms, across a broad range of network evaluated while considering other mechanisms, across a broad range
topologies and with attention to the impact on traffic sharing the of network topologies and with attention to the impact on traffic
capacity. If increased use of transport header encryption results sharing the capacity. If increased use of transport header
in reduced availability of open data, it could eliminate the encryption results in reduced availability of open data, it could
independent self-checks to the standardisation process that have eliminate the independent self-checks to the standardisation
previously been in place from research and academic contributors process that have previously been in place from research and
(e.g., the role of the IRTF Internet Congestion Control Research academic contributors (e.g., the role of the IRTF Internet
Group (ICCRG) and research publications in reviewing new transport Congestion Control Research Group (ICCRG) and research
mechanisms and assessing the impact of their deployment). publications in reviewing new transport mechanisms and assessing
the impact of their deployment).
Observable transport information might be useful to various Observable transport header information might be useful to various
stakeholders. Other stakeholders have incentives to limit what can stake holders. Other stake holders have incentives to limit what can
be observed. This document does not make recommendations about what be observed. This document does not make recommendations about what
information ought to be exposed, to whom it ought to be observable, information ought to be exposed, to whom it ought to be observable,
or how this will be achieved. There are also design choices about or how this will be achieved. There are also design choices about
where observable fields are placed. For example, one location could where observable fields are placed. For example, one location could
be a part of the transport header outside of the encryption envelope, be a part of the transport header outside of the encryption envelope,
another alternative is to carry the information in a network-layer another alternative is to carry the information in a network-layer
extension header. New transport protocol designs ought to explicitly option or extension header. New transport protocol designs ought to
identify any fields that are intended to be observed, consider if explicitly identify any fields that are intended to be observed,
there are alternative ways of providing the information, and reflect consider if there are alternative ways of providing the information,
on the implications of observable fields being used by network and reflect on the implications of observable fields being used by
devices, and how this might impact user privacy and protocol network devices, and how this might impact user privacy and protocol
evolution when these fields become ossified. evolution when these fields become ossified.
As [RFC7258] notes, "Making networks unmanageable to mitigate As [RFC7258] notes, "Making networks unmanageable to mitigate
(pervasive monitoring) is not an acceptable outcome, but ignoring (pervasive monitoring) is not an acceptable outcome, but ignoring
(pervasive monitoring) would go against the consensus documented (pervasive monitoring) would go against the consensus documented
here." Providing explicit information can help avoid traffic being here." Providing explicit information can help avoid traffic being
inappropriately classified, impacting application performance. An inappropriately classified, impacting application performance. An
appropriate balance will emerge over time as real instances of this appropriate balance will emerge over time as real instances of this
tension are analysed [RFC7258]. This balance between information tension are analysed [RFC7258]. This balance between information
exposed and information hidden ought to be carefully considered when exposed and information hidden ought to be carefully considered when
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transport protocols. Issues relating to security are discussed transport protocols. Issues relating to security are discussed
throughout this document. throughout this document.
Authentication, confidentiality protection, and integrity protection Authentication, confidentiality protection, and integrity protection
are identified as Transport Features by [RFC8095]. As currently are identified as Transport Features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a deployed in the Internet, these features are generally provided by a
protocol or layer on top of the transport protocol 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 or to
Integrity checks can protect an endpoint from undetected modification modify an existing transport. Integrity checks can protect an
of protocol fields by network devices, whereas encryption and endpoint from undetected modification of protocol fields by network
obfuscation or greasing can further prevent these headers being devices, whereas encryption and obfuscation or greasing can further
utilised by network devices. Preventing observation of headers prevent these headers being utilised by network devices. Preventing
provides an opportunity for greater freedom to update the protocols observation of headers provides an opportunity for greater freedom to
and can ease experimentation with new techniques and their final update the protocols and can ease experimentation with new techniques
deployment in endpoints. A protocol specification needs to weigh the and their final deployment in endpoints. A protocol specification
costs of ossifying common headers, versus the potential benefits of needs to weigh the costs of ossifying common headers, versus the
exposing specific information that could be observed along the potential benefits of exposing specific information that could be
network path to provide tools to manage new variants of protocols. observed along the network path to provide tools to manage new
variants of protocols.
A protocol design that uses header encryption can provide Header encryption can provide confidentiality of some or all of the
confidentiality of some or all of the protocol header information. transport header information. This prevents an on-path device from
This prevents an on-path device from knowledge of the header field. knowledge of the header field. It therefore prevents mechanisms
It therefore prevents mechanisms being built that directly rely on being built that directly rely on the information or seeks to infer
the information or seeks to infer semantics of an exposed header semantics of an exposed header field. Reduces visibility into
field. Reduces visibility into transport metadata can limit the transport metadata can limit the ability to measure and characterise
ability to measure and characterise traffic. It can also provide traffic. It can also provide privacy benefits in some cases.
privacy benefits in some cases.
Extending the transport payload security context to also include the Extending the transport payload security context to also include the
transport protocol header protects both information with the same transport protocol header protects both information with the same
key. A privacy concern would arise if this key was shared with a key. A privacy concern would arise if this key was shared with a
third party, e.g., providing access to transport header information third party, e.g., providing access to transport header information
to debug a performance issue, would also result in exposing the to debug a performance issue, would also result in exposing the
transport payload data to the same third party. A layered security transport payload data to the same third party. Such risks would be
design that separates network data from payload data would avoid such mitigated using a layered security design that provides one domain of
risks. protection and associated keys for the transport payload and
encrypted transport headers; and a separate domain of protection and
associated keys for any observable transport header fields.
Exposed transport headers are sometimes utilised as a part of the Exposed transport headers are sometimes utilised as a part of the
information to detect anomalies in network traffic. "While PM is an information to detect anomalies in network traffic. "While PM is an
attack, other forms of monitoring that might fit the definition of PM attack, other forms of monitoring that might fit the definition of PM
can be beneficial and not part of any attack, e.g., network can be beneficial and not part of any attack, e.g., network
management functions monitor packets or flows and anti-spam management functions monitor packets or flows and anti-spam
mechanisms need to see mail message content." [RFC7258]. This can mechanisms need to see mail message content." [RFC7258]. This can
be used as the first line of defence to identify potential threats be used as the first line of defence to identify potential threats
from DOS or malware and redirect suspect traffic to dedicated nodes from DOS 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 normalisation 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 can also form a part of the Exposed transport header fields can also form a part of the
information used by the receiver of a transport protocol to protect information used by the receiver of a transport protocol to protect
the transport layer from data injection by an attacker. In the transport layer from data injection by an attacker. In
evaluating this use of exposed header information, it is important to evaluating this use of exposed header information, it is important to
consider whether it introduces a significant DOS threat. For consider whether it introduces a significant DOS threat. For
example, an attacker could construct a DOS attack by sending packets example, an attacker could construct a DOS attack by sending packets
skipping to change at page 38, line 40 skipping to change at page 40, line 9
space that is encrypted; or by verifying an encrypted token not space that is encrypted; or by verifying an encrypted token not
visible to an attacker). This would also mitigate against on-path visible to an attacker). This would also mitigate against on-path
attacks. An additional processing cost can be incurred when attacks. An additional processing cost can be incurred when
decryption has to be attempted before a receiver is able to discard decryption has to be attempted before a receiver is able to discard
injected 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 header information. Open
accessibility to tools that can help understand trends in application data, and accessibility to tools that can help understand trends in
deployment, network traffic and usage patterns can all contribute to application deployment, network traffic and usage patterns can all
understanding security challenges. contribute to understanding security challenges.
The Security and Privacy Considerations in the Framework for Large- The Security and Privacy Considerations in the Framework for Large-
Scale Measurement of Broadband Performance (LMAP) [RFC7594] contain Scale Measurement of Broadband Performance (LMAP) [RFC7594] contain
considerations for Active and Passive measurement techniques and considerations for Active and Passive measurement techniques and
supporting material on measurement context. supporting material on measurement context.
9. IANA Considerations 9. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX XX RFC ED - PLEASE REMOVE THIS SECTION XXX
skipping to change at page 40, line 34 skipping to change at page 42, line 5
[Measurement] [Measurement]
Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement- 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-
trace". trace".
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998, DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>. <https://www.rfc-editor.org/info/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>. <https://www.rfc-editor.org/info/rfc2475>.
skipping to change at page 43, line 23 skipping to change at page 44, line 46
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437, "IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011, DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>. <https://www.rfc-editor.org/info/rfc6437>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>. <https://www.rfc-editor.org/info/rfc6438>.
[RFC7126] Gont, F., Atkinson, R., and C. Pignataro, "Recommendations
on Filtering of IPv4 Packets Containing IPv4 Options",
BCP 186, RFC 7126, DOI 10.17487/RFC7126, February 2014,
<https://www.rfc-editor.org/info/rfc7126>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>. 2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF [RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF
Recommendations Regarding Active Queue Management", Recommendations Regarding Active Queue Management",
BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015, BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,
<https://www.rfc-editor.org/info/rfc7567>. <https://www.rfc-editor.org/info/rfc7567>.
[RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T., [RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
skipping to change at page 45, line 5 skipping to change at page 46, line 28
Explicit Congestion Notification (ECN)", RFC 8087, Explicit Congestion Notification (ECN)", RFC 8087,
DOI 10.17487/RFC8087, March 2017, DOI 10.17487/RFC8087, March 2017,
<https://www.rfc-editor.org/info/rfc8087>. <https://www.rfc-editor.org/info/rfc8087>.
[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind, [RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
Ed., "Services Provided by IETF Transport Protocols and Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Mechanisms", RFC 8095, Congestion Control Mechanisms", RFC 8095,
DOI 10.17487/RFC8095, March 2017, DOI 10.17487/RFC8095, March 2017,
<https://www.rfc-editor.org/info/rfc8095>. <https://www.rfc-editor.org/info/rfc8095>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6 [RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6
Performance and Diagnostic Metrics (PDM) Destination Performance and Diagnostic Metrics (PDM) Destination
Option", RFC 8250, DOI 10.17487/RFC8250, September 2017, Option", RFC 8250, DOI 10.17487/RFC8250, September 2017,
<https://www.rfc-editor.org/info/rfc8250>. <https://www.rfc-editor.org/info/rfc8250>.
[RFC8289] Nichols, K., Jacobson, V., McGregor, A., Ed., and J. [RFC8289] Nichols, K., Jacobson, V., McGregor, A., Ed., and J.
Iyengar, Ed., "Controlled Delay Active Queue Management", Iyengar, Ed., "Controlled Delay Active Queue Management",
RFC 8289, DOI 10.17487/RFC8289, January 2018, RFC 8289, DOI 10.17487/RFC8289, January 2018,
<https://www.rfc-editor.org/info/rfc8289>. <https://www.rfc-editor.org/info/rfc8289>.
skipping to change at page 48, line 10 skipping to change at page 50, line 10
-10 Updated following additional feedback from 1st WGLC. Comments -10 Updated following additional feedback from 1st WGLC. Comments
from David Black; Tommy Pauly; Ian Swett; Mirja Kuehlewind; Peter from David Black; Tommy Pauly; Ian Swett; Mirja Kuehlewind; Peter
Gutmann; Ekr; and many others via the TSVWG list. Some people Gutmann; Ekr; and many others via the TSVWG list. Some people
thought that "needed" and "need" could represent requirements in the thought that "needed" and "need" could represent requirements in the
document, etc. this has been clarified. document, etc. this has been clarified.
-11 Updated following additional feedback from Martin Thomson, and -11 Updated following additional feedback from Martin Thomson, and
corrections from other reviewers. corrections from other reviewers.
-11 Updated following additional feedback from reviewers. -12 Updated following additional feedback from reviewers.
-13 Updated following 2nd WGLC with comments from D.L.Black; T.
Herbert; Ekr; and other reviewers.
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
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