draft-ietf-tsvwg-transport-encrypt-08.txt   draft-ietf-tsvwg-transport-encrypt-09.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: February 24, 2020 University of Glasgow Expires: May 6, 2020 University of Glasgow
August 23, 2019 November 3, 2019
The Impact of Transport Header Confidentiality on Network Operation and Considerations around Transport Header Confidentiality, Network
Evolution of the Internet Operations, and the Evolution of Internet Transport Protocols
draft-ietf-tsvwg-transport-encrypt-08 draft-ietf-tsvwg-transport-encrypt-09
Abstract Abstract
This document describes some implications of applying end-to-end To protect user data and privacy, Internet transport protocols have
encryption at the transport layer. It first identifies in-network supported payload encryption and authentication for some time. Such
uses of transport layer header information. Then, it reviews some encryption and authentication is now also starting to be applied to
implications of developing end-to-end transport protocols that use the transport protocol headers. This helps avoid transport protocol
encryption to provide confidentiality of the transport protocol ossification by middleboxes, while also protecting metadata about the
headers, or that use authentication to protect the integrity of communication. Current operational practice in some networks inspect
transport header information. Since measurement and analysis of the transport header information within the network, but this is no
impact of network characteristics on transport protocols has been longer possible when those transport headers are encrypted. This
important to the design of current transports, it also considers the document discusses the possible impact when network traffic uses a
impact of transport encryption on transport and application protocol with an encrypted transport header. It suggests issues to
evolution. consider when designing new transport protocols, to account for
network operations, prevent network ossification, and enable
transport evolution, while still respecting 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 February 24, 2020. This Internet-Draft will expire on May 6, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 3 2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 4
2.1. Use of Transport Header Information in the Network . . . 4 2.1. Use of Transport Header Information in the Network . . . 5
2.2. Encryption of Transport Header Information . . . . . . . 5 2.2. Authentication of Transport Header Information . . . . . 6
2.3. Encryption tradeoffs . . . . . . . . . . . . . . . . . . 6 2.3. Observable Transport Header Fields . . . . . . . . . . . 7
3. Current uses of Transport Headers within the Network . . . . 8 3. Current uses of Transport Headers within the Network . . . . 10
3.1. Observing Transport Information in the Network . . . . . 9 3.1. Observing Transport Information in the Network . . . . . 11
3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 15 3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 17
3.3. Use for Network Diagnostics and Troubleshooting . . . . . 19 3.3. Use for Network Diagnostics and Troubleshooting . . . . . 21
3.4. Header Compression . . . . . . . . . . . . . . . . . . . 20 3.4. Header Compression . . . . . . . . . . . . . . . . . . . 22
4. Encryption and Authentication of Transport Headers . . . . . 21 4. Encryption and Authentication of Transport Headers . . . . . 23
5. Addition of Transport Information to Network-Layer Protocol 5. Addition of Transport Information to Network-Layer Headers . 26
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 5.1. Use of OAM within a Maintenance Domain . . . . . . . . . 26
6. Implications of Protecting the Transport Headers . . . . . . 25 5.2. Use of OAM across Multiple Maintenance Domains . . . . . 26
6.1. Independent Measurement . . . . . . . . . . . . . . . . . 26 6. Implications of Protecting the Transport Headers . . . . . . 27
6.2. Characterising "Unknown" Network Traffic . . . . . . . . 28 6.1. Independent Measurement . . . . . . . . . . . . . . . . . 27
6.3. Accountability and Internet Transport Protocols . . . . . 28 6.2. Characterising "Unknown" Network Traffic . . . . . . . . 29
6.4. Impact on Operational Cost . . . . . . . . . . . . . . . 28 6.3. Accountability and Internet Transport Protocols . . . . . 30
6.5. Impact on Research, Development and Deployment . . . . . 29 6.4. Impact on Operational Cost . . . . . . . . . . . . . . . 30
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.5. Impact on Research, Development and Deployment . . . . . 31
8. Security Considerations . . . . . . . . . . . . . . . . . . . 33 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 32
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 8. Security Considerations . . . . . . . . . . . . . . . . . . . 35
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
11. Informative References . . . . . . . . . . . . . . . . . . . 36 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37
Appendix A. Revision information . . . . . . . . . . . . . . . . 43 11. Informative References . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44 Appendix A. Revision information . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
1. Introduction 1. Introduction
There is increased interest in, and deployment of, protocols that Transport protocols have supported end-to-end encryption of payload
employ end-to-end encryption at the transport layer, including the data for many years. Examples include Transport Layer Security (TLS)
transport layer headers. An example of such a transport is the QUIC over TCP [RFC8446], Datagram TLS (DTLS) over UDP [RFC6347], and their
transport protocol [I-D.ietf-quic-transport], currently being corresponding usage guidelines [RFC7525], Secure RTP [RFC3711], and
standardised in the IETF. Encryption of transport layer headers and TCPcrypt [RFC8548] which permits opportunistic encryption of the TCP
payload data has many benefits in terms of protecting user privacy. transport payload. Some of these also provide integrity protection
These benefits have been widely discussed [RFC7258], [RFC7624], and of all or part of the transport header.
this document strongly supports the increased use of encryption in
transport protocols. Encryption and authentication can also be used
to prevent unwanted modification of transport header information by
middleboxes. There are also, however, some costs, in that the
widespread use of transport encryption requires changes to network
operations, and complicates network measurement for research,
operational, and standardisation purposes. The direction in which
the use of transport header confidentiality evolves could have
significant implications on the way the Internet architecture
develops, and therefore needs to be considered as a part of protocol
design.
The remainder of this document discusses some consequences of This end-to-end transport payload encryption brings many benefits in
applying end-to-end encryption at the transport layer. It reviews terms of providing confidentiality and protecting user privacy. Such
the implications of developing end-to-end transport protocols that benefits have been widely discussed [RFC7258] [RFC7624]. This
use encryption to provide confidentiality of the transport protocol document strongly supports and encourages increased use of end-to-end
headers, and considers the effect of such changes on transport payload encryption in transport protocols. The implications of
protocol design and network operations. It also considers some protecting the transport payload data are therefore not further
anticipated implications on transport and application evolution. discussed in this document.
Transports are also increasingly encrypting and authenticating the A further level of protection can be achieved by encrypting the
payload (i.e., the application data carried within the transport entire network layer payload, including both the transport layer
connection) end-to-end. Such protection is encouraged, and the headers and the payload. This method provides confidentiality for
implications of protecting the payload are not further discussed in the entire transport packet. It therefore does not expose any
this document. transport information to devices in the network, and prevents
modification along a network path. An example of encryption at the
network layer is the IPsec Encapsulating Security Payload (ESP)
[RFC4303] in tunnel mode. Some Virtual Private Network (VPN) methods
also encrypt these headers. This form of encryption is not further
discussed in this document.
There is also a middle ground, comprising transport protocols that
encrypt some, or all, of their transport layer header information, in
addition to the payload. An example of such a protocol, that is
seeing widespread interest and deployment, is the QUIC transport
protocol [I-D.ietf-quic-transport]. Encryption and authentication of
the transport header information can prevent unwanted modification of
transport headers by middleboxes. It also reduces the amount of
metadata about the progress of the transport connection that is
visible to the network.
As discussed in [RFC7258], Pervasive Monitoring (PM) nis a technical
attack that needs to be mitigated in the design of IETF protocols.
This document supports that conclusion and the use of transport
header encryption to protect against pervasive monitoring. RFC 7258
also notes, though, that "Making networks unmanageable to mitigate PM
is not an acceptable outcome, but ignoring PM would go against the
consensus documented here. An appropriate balance will emerge over
time as real instances of this tension are considered".
The following sections further considers some of the costs and
changes to network management and research that are implied by
widespread use of transport protocols that encrypt the transport
header information. It reviews the implications of developing
transport protocols that use end-to-end encryption to provide
confidentiality of their transport layer headers, and considers the
effect of such changes on transport protocol design and network
operations. It also considers some anticipated implications on
transport and application evolution. That is, it considers the
issues in designing transport protocols that both protect their
header information and respect user privacy.
2. Context and Rationale 2. Context and Rationale
The transport layer provides end-to-end interactions between The transport layer provides end-to-end interactions between
endpoints (processes) using an Internet path. Transport protocols endpoints (processes) using an Internet path. Transport protocols
layer directly over the network-layer service, and are sent in the layer directly over the network-layer service, and are sent in the
payload of network-layer packets. They support end-to-end payload of network-layer packets. They support end-to-end
communication between applications, supported by higher-layer communication between applications, using higher-layer protocols
protocols, running on the end systems (transport endpoints). This running on the end systems (transport endpoints).
simple architectural view hides one of the core functions of the
This simple architectural view hides one of the core functions of the
transport: to discover and adapt to the Internet path that is transport: to discover and adapt to the Internet path that is
currently used. The design of Internet transport protocols is as currently being used. The design of Internet transport protocols is
much about trying to avoid the unwanted side effects of congestion on as much about trying to avoid the unwanted side effects of congestion
a flow and other capacity-sharing flows, avoiding congestion on a flow and other capacity-sharing flows, avoiding congestion
collapse, adapting to changes in the path characteristics, etc., as collapse, adapting to changes in the path characteristics, etc., as
it is about end-to-end feature negotiation, flow control, and it is about end-to-end feature negotiation, flow control, and
optimising for performance of a specific application. optimising for performance of a specific application.
To achieve stable Internet operations, the IETF transport community To achieve stable Internet operations, the IETF transport community
has to date relied heavily on the results of measurements and the has to date relied heavily on the results of measurements and the
insights of the network operations community to understand the trade- insights of the network operations community to understand the trade-
offs, and to inform selection of appropriate mechanisms to ensure a offs, and to inform selection of appropriate mechanisms to ensure a
safe, reliable, and robust Internet (e.g., [RFC1273]). In turn, the safe, reliable, and robust Internet (e.g., [RFC1273]). In turn, the
network operator and access provider community has relied on being network operator and access provider communities have relied on being
able to understand the pattern and requirements of traffic passing able to understand the pattern and requirements of traffic passing
over the Internet, both in aggregate and at the flow level. The over the Internet, both in aggregate and at the flow level. The
widespread use of transport header encryption may change this. widespread use of transport header encryption could change this.
2.1. Use of Transport Header Information in the Network
In-network measurement of transport flow characteristics can be used
to enhance performance, and control cost and service reliability.
Some operators have deployed functionality in middleboxes to both
support network operations and enhance performance. This reliance on
the presence and semantics of specific header information leads to
ossification, where an endpoint could be required to supply a
specific header to receive the network service that it desires. In
some cases, this could be benign or advantageous to the protocol
(e.g., recognising the start of a connection, or explicitly exposing
protocol information can be expected to provide more consistent
decisions by on-path devices than the use of diverse methods to infer
semantics from other flow properties). In other cases, the
ossification could frustrate the evolution of the protocol (e.g., a
mechanism implemented in a network device, such as a firewall, that
required a header field to have only a specific known set of values
would prevent the device from forwarding packets using a different
version of a protocol that introduces a feature that changes the
value of this field).
As an example of ossification, consider the experience of developing
Transport Layer Security (TLS) 1.3 [RFC8446]. This required a design
that recognised that deployed middleboxes relied on the presence of
certain header filed exposed in TLS 1.2, and failed if those headers
were changed. Other examples of the impact of ossification can be
found in the development of Multipath TCP (MPTCP) and the TCP Fast
Open option. The design of MPTCP had to be revised to account for
middleboxes, so called "TCP Normalizers", that monitor the evolution
of the window advertised in the TCP headers and that reset
connections if the window does not grow as expected. Similarly, TCP
Fast Open has had issues with middleboxes that remove unknown TCP
options, that drop segments with unknown TCP options, that drop
segments that contain data and have the SYN bit set, that drop
packets with SYN/ACK that acknowledge data, or that disrupt
connections that send data before the three-way handshake completes.
In all these cases, the issue was caused by middleboxes that had a
hard-coded understanding of transport behaviour, and that interacted
poorly with transports that tried to change that behaviour. Other
examples have included middleboxes that rewrite TCP sequence and
acknowledgement numbers but are unaware of the (newer) SACK option
and don't correctly rewrite selective acknowledgements to match the
changes made to the fixed TCP header.
2.2. Encryption of Transport Header Information
Encryption is expected to form a basis for many future transport Encryption is expected to form a core part of future transport
protocol designs. These can be in the form of encrypted transport protocol designs. This can be in the form of encrypted transport
protocols (i.e., transport protocols that use encryption to provide protocols (i.e., transport protocols that use encryption to provide
confidentiality of some or all of the transport-layer header confidentiality of some or all of the transport-layer header
information), and/or the encryption of transport payloads (i.e., information), and/or the encryption of transport payloads (i.e.,
confidentiality of the payload data). There are many motivations for confidentiality of the payload data). There are many motivations for
deploying such transports, and increasing public concerns about deploying such transports. Increasing public concerns about
interference with Internet traffic [RFC7624] have led to a rapidly interference with Internet traffic [RFC7624] have led to a rapidly
expanding deployment of encrypted transport protocols such as QUIC expanding deployment of encrypted transport protocols such as QUIC
[I-D.ietf-quic-transport]. Using encryption to provide [I-D.ietf-quic-transport].
confidentiality of the transport layer therefore brings some well-
known privacy and security benefits.
Authentication and the introduction of cryptographic integrity checks Using encryption to provide confidentiality of the transport layer
for header fields can prevent undetected manipulation of transport therefore brings some well-known privacy and security benefits.
headers by network devices. This does not prevent inspection of the
information by devices on path, and it is possible that such devices
could develop mechanisms that rely on the presence of such a field or
a known value in the field. In this context, specification of a non-
encrypted transport header field explicitly allows protocol designers
to make the certain header information observable by the network.
This supports use of this information by on-path devices, but at the
same time can be expected to lead to ossification of the transport
header, because network forwarding could evolve to depend on the
presence and/or value of these fields. To avoid unwanted inspection,
a protocol could intentionally vary the format or value of exposed
header fields [I-D.ietf-tls-grease].
A protocol design that uses header encryption with secure key 2.1. Use of Transport Header Information in the Network
distribution can provide confidentiality for some, or all, of the
protocol header information. This prevents an on-path device from
observing the transport headers, and stops mechanisms being built
that directly rely on transport header information, or that seek to
infer semantics of exposed header fields. Transport header
encryption can therefore help reduce ossification of the transport
layer.
While encryption can hide transport header information, it does not In-network measurement of transport flow characteristics can be used
to enhance performance, and control cost and service reliability. To
support network operations and enhance performance, some operators
have deployed functionality that utilises on-path observations of the
transport headers of packets passing through their network. These
devices can rely on the presence and semantics of specific header
information, which leads to ossification where an endpoint has to
supply a specific header to receive the network service that it
desires.
In some cases, network-layer use of transport header information can
be benign or advantageous to the protocol (e.g., recognising the
start of a TCP connection, providing header compression for a Secure
RTP flow, or explicitly using exposed protocol information to provide
consistent decisions by on-path devices). However, in other cases,
ossification can frustrate the evolution of the transport protocol.
A mechanism implemented in a network device, such as a firewall, that
requires a header field to have only a specific known set of values
(i.e., that regards the field as invariant) can prevent the device
from forwarding packets using a different version of a protocol that
introduces a feature that changes the value of the observed field.
An example of such ossification was observed in the development of
Transport Layer Security (TLS) 1.3 [RFC8446]. This necessitated a
design that recognised that deployed middleboxes relied on the
presence of certain header fields exposed in TLS 1.2, and failed if
those headers were changed.
The design of MPTCP also had to be revised to account for middleboxes
(known as "TCP Normalizers") that monitor the evolution of the window
advertised in the TCP header and reset connections when the window
does not grow as expected. Similarly, Issues have been reported with
TCP Fast Open using middleboxes that modify the transport header of
packets by removing unknown TCP options, that drop segments with
unknown TCP options, drop segments that contain data and have the SYN
bit set, drop packets with SYN/ACK that acknowledge data, or that
disrupt connections that send data before the three-way handshake
completes. Other examples of ossification have included middleboxes
that rewrite TCP sequence and acknowledgement numbers, but are
unaware of the (newer) TCP selective acknowledgement (SACK) Option
and therefore fail to correctly rewrite the selective acknowledgement
header information to match the changes that were made to the fixed
TCP header.
In all these cases, the issue was caused by middleboxes that had a
hard-coded understanding of transport behaviour, and that interacted
poorly with transport protocols when the transport behaviour changed.
Many protocol specifications had also failed to clearly indicate the
invariant parts of the transport header and were designed without
thought for how header information could be used within the network.
Transport header encryption can help reduce such ossification of the
transport layer. A protocol design that uses header encryption with
secure key distribution can provide confidentiality for some, or all,
of the protocol header information. This prevents an on-path device
from observing the transport headers, and stops mechanisms being
built that directly rely on transport header information, or that
seek to infer semantics of exposed header fields. This encryption is
normally combined with authentication of the protected information.
RFC 8546 summarises this, stating that it is "The wire image, not the
protocol's specification, determines how third parties on the network
paths among protocol participants will interact with that protocol"
[RFC8546].
While encryption can hide transport header information and therefore
help to reduce ossification of the transport protocol, it does not
prevent ossification of the network service. People seeking to prevent ossification of the network service. People seeking to
understand network traffic could come to rely on pattern inferences understand network traffic could come to rely on pattern inferences
and other heuristics as the basis for network decision and to derive and other heuristics as the basis for network decision and to derive
measurement data. This can create new dependencies on the transport measurement data. This can create new dependencies on the transport
protocol, or the patterns of traffic it can generate. This use of protocol, or the patterns of traffic it can generate. This use of
machine-learning methods usually demands large data sets, presenting machine-learning methods usually demands large data sets, presenting
it own requirements for collecting and distributing the data. it own requirements for collecting and distributing the data.
2.3. Encryption tradeoffs 2.2. Authentication of Transport Header Information
The are architectural challenges and considerations in the way The design of a transport protocol needs to determine whether to
transport protocols are designed, and the ability to characterise and encrypt all or a part of the transport information. It is possible
compare different transport solutions [Measure]. The decision about that on-path devices could develop mechanisms that rely on the
which transport headers fields are made observable offers trade-offs presence of any non-encrypted field, or a known value in the field.
around authentication and confidentiality versus observability, Section 4 of RFC8558 goes further, to state: "Anything exposed to the
network operations and management, and ossification. The impact path should be done with the intent that it be used by the network
differs depending on the activity, for example: elements on the path" [RFC8558]. In this context, specification of a
non-encrypted transport header field explicitly allows protocol
designers to make the certain header information observable by the
network. This supports use of this information by on-path devices,
but at the same time this can lead to ossification of the exposed
part of a transport header. That is, network forwarding could evolve
to depend on the presence and/or value of these fields (even if the
header is not modified by the in-network device).
Network Operations and Research: Observable transport headers enable New protocol designs will make use of authentication to provide a
explicit measure and analysis protocol performance, network cryptographic integrity check for the transport header fields.
anomalies, and failure pathologies at any point along the Internet Transport header information that is authenticated, but not
path. In many cases, it is important to relate observations to encrypted, permits inspection of the non-encrypted header fields by
specific equipment/configurations or network segments. devices on the path, but does prevent undetected manipulation by
network devices.
Concealing transport header information makes performance/ Sometimes a protocol design employs a header field that is not
behaviour unavailable to passive observers along the path, encrypted, but it is desired to avoid unwanted inspection restricting
Operators will be unable to use this information directly and may the choice of usable values in the field (and the resulting potential
turn to more ambitious ways to collect, estimate, or infer that for undesirable ossification). In this case, the protocol designers
data. Operational practices aimed at guessing transport can choose to intentionally vary the format and/or value of exposed
parameters are out of scope for this document, and are only header fields to reduce the chance of ossification (see Section 4 and
mentioned here to recognize that encryption does not prevent [I-D.ietf-tls-grease]).
operators from attempting to apply practices that were used with
unencrypted transport headers.
Confidentiality of the transport payload could be provided while 2.3. Observable Transport Header Fields
leaving some, or all, transport headers unencrypted (or providing
this information in a network-layer extension), possibly with
authentication. This provides many of the privacy and security
benefits while supporting operations and research, but at the cost
of ossifying the exposed headers.
Protection from Denial of Service: Observable transport headers Transport headers have end-to-end meaning, but are often observed by
currently provide useful input to classify and detect anomalous equipment within the network. The decision about which transport
events, such as changes in application behaviour or distributed headers fields are made observable offers trade-offs around header
denial of service attacks. For this application to be effective, confidentiality versus header observability (including non-encrypted
it needs to be possible for an operator to uniquely disambiguate but authenticated header fields) for network operations and
unwanted traffic. Concealing transport header information would management, and the implications for ossification and user privacy.
prevent disambiguation based on transport information. This could The impact differs depending on the activity, as discussed below and
result in less-efficient identification of unwanted traffic, the developed in the remainder of this document:
use of heuristics to identify anomalous flows, or the introduction
of rate limits for uncharacterised traffic.
Network Troubleshooting and Diagnostics: Observable transport Network Operations: Observable transport headers enable explicit
headers can be utilised by operators for network troubleshooting measurement and analysis of protocol performance,
and diagnostics. Flows experiencing packet loss or jitter are network anomalies, and failure pathologies at any
hard to distinguish from unaffected flows when only observing point along the Internet path. In many cases, it
network layer headers. Effective troubleshooting often requires is important to relate observations to specific
visibility into the transport layer behaviour. equipment/configurations or a specific network
segment.
Concealing transport header information reduces the incentive for Concealing transport header information makes
operators to troubleshoot, since they cannot interpret the data. performance/behaviour unavailable to passive
It can limit understanding of transport dynamics, such as the observers along the path. Operators will then be
impact of packet loss or latency on the flows, or make it harder unable to use this information directly and could
to localise the network segment intoducing the packet loss or turn to more ambitious ways to collect, estimate,
latency. Additional mechanisms will be needed to help reconstruct or infer that data. (Operational practices aimed
or replace transport-level metrics for troubleshooting and at guessing transport parameters are out of scope
diagnostics. These can add complexity and operational costs for this document, and are only mentioned here to
(e.g., in deploying additional functions in equipment or adding recognize that encryption does not stop operators
traffic overhead). from attempting to apply practices that have been
used with unencrypted transport headers.)
See also Sections 3, 5, and 6.4.
Network Traffic Analysis: Observable transport headers can support Traffic Analysis: Observable transport headers can be used to
network traffic analysis to determine which transport protocols determine which transport protocols and features
and features are being used across a network segment and to are being used across a network segment, and to
measure trends in the pattern of usage. For some applications measure trends in the pattern of usage. For some
end-to-end measurements/traces are sufficient, but in other use cases, end-to-end measurements/traces are
applications it is important to relate observations to specific sufficient and can assist in developing and
equipment/configurations or particular network segments. debugging new transports and analysing their
deployment. In other uses, it is important to
relate observations to specific equipment/
configurations or particular network segments.
Concealing transport header information can make analysis harder Concealing transport header information can make
or impossible. This could impact the ability for an operator to analysis harder or impossible. This could impact
anticipate the need for network upgrades and roll-out. It can the ability to anticipate the need for network
also impact the on-going traffic engineering activities performed upgrades and roll-out, or affect on-going traffic
by operators, such as determining which parts of the path engineering activities performed by operators
contribute delay, jitter or loss. While this impact could, in such as determining which parts of the path
many cases, be small, there are scenarios where operators directly contribute delay, jitter, or loss. While this
support particular services and need visibility to explore issues impact could, in many cases, be small, there are
relating to Quality of Service (QoS), the ability to perform fast scenarios where operators will actively monitor
re-routing of critical traffic, or to mitigate the characteristics and support particular services, e.g., to explore
of specific radio links, and so on. issues relating to Quality of Service (QoS), to
perform fast re-routing of critical traffic, to
mitigate the characteristics of specific radio
links, and so on.
Open and Verifiable Network Data: Observable transport headers can See also Sections 3.1-3.2, and 5.
provide open and verifiable measurement data. The ability of
other stake holders to review transport header traces helps
develop insight into performance and traffic contribution of
specific variants of a protocol. Independently observed data is
important to help ensure the health of the research and
development communities.
Concealing transport header information can reduce the range of Troubleshooting: Observable transport headers can be utilised by
actors that can observe useful data. This would limit the operators for network troubleshooting and
information sources available to the Internet community to diagnostics. Effective troubleshooting often
understand the operation of new transport protocols, reducing requires visibility into the transport layer
information to inform design decisions and standardisation of the behaviour. Flows experiencing packet loss or
new protocols and related operational practices. jitter are hard to distinguish from unaffected
flows when only observing network layer headers.
Compliance: Observable transport headers coupled with published Concealing transport header information reduces
transport specifications allow operators and regulators to check the incentive for operators to troubleshoot,
compliance. Independently verifiable performance metrics can also since they cannot interpret the data. This can
be utilised to demonstrate regulatory compliance in some limit understanding of transport dynamics, such
jurisdictions, and as a basis for informing design decisions. as the impact of packet loss or latency on the
This can bring assurance to those operating networks, often flows, or make it harder to localise the network
avoiding the need to deploy complex techniques that routinely segment introducing the packet loss or latency.
monitor and manage Internet traffic flows (e.g., avoiding the Additional mechanisms will be needed to help
capital and operational costs of deploying flow rate-limiting and reconstruct or replace transport-level metrics
network circuit-breaker methods [RFC8084]). for troubleshooting and diagnostics. These can
add complexity and operational costs (e.g., in
deploying additional functions in equipment or
adding traffic overhead).
When transport header information is concealed, it is not possible See also Section 3.3 and 5.
to observe transport header information. Methods are still needed
to confirm that the traffic produced conforms to the expectations
of the operator or developer.
Different parties will view the relative importance of these issues Network Protection: Observable transport headers currently provide
differently. For some, the benefits of encrypting some, or all, of useful input to classify and detect anomalous
the transport headers may outweigh the impact of doing so; others events, such as changes in application behaviour
might make a different trade-off. The purpose of highlighting the or distributed denial of service attacks. An
trade-offs is to make such analysis possible. operator needs to uniquely disambiguate unwanted
traffic.
Concealing transport header information would
prevent disambiguation based on transport
information. This could result in less-efficient
identification of unwanted traffic, the use of
heuristics to identify anomalous flows, or the
introduction of rate limits for uncharacterised
traffic.
See also Sections 6.2 and 6.3.
SLA Compliance: Observable transport headers coupled with
published transport specifications allow
operators and regulators to explore teh
compliance with Service Level Agreements (SLAs).
Independently verifiable performance metrics can
also be utilised to demonstrate regulatory
compliance in some jurisdictions, and as a basis
for informing design decisions. This can bring
assurance to those operating networks, often
avoiding the need to deploy complex techniques
that routinely monitor and manage Internet
traffic flows (e.g., avoiding the capital and
operational costs of deploying flow rate-limiting
and network circuit-breaker methods [RFC8084]).
When transport header information is concealed,
it is not possible to observe transport header
information. Methods are still needed to confirm
that the traffic produced conforms to the
expectations of the operator or developer.
See also Sections 5 and 6.1-6.3.
Verifiable Data: Observable transport headers can provide open and
verifiable measurements to support operations,
research, and protocol development. The ability
of other stake holders to review transport header
traces helps develop insight into performance and
traffic contribution of specific variants of a
protocol. Independently observed data is
important to help ensure the health of the
research and development communities.
Concealing transport header information can
reduce the range of actors that can observe
useful data. This limits the information sources
available to the Internet community to understand
the operation of new transport protocols,
reducing information to inform design decisions
and standardisation of the new protocols and
related operational practices
See also Section 6.
There are architectural challenges and considerations in the way
transport protocols are designed, and the ability to characterise and
compare different transport solutions [Measure]. Different parties
will view the relative importance of these differently. For some,
the benefits of encrypting the transport headers could outweigh the
impact of doing so; others might make a different trade-off.
3. Current uses of Transport Headers within the Network 3. Current uses of Transport Headers within the Network
Despite transport headers having end-to-end meaning, some of these In response to pervasive monitoring [RFC7624] revelations and the
transport headers have come to be used in various ways within the IETF consensus that "Pervasive Monitoring is an Attack" [RFC7258],
Internet. In response to pervasive monitoring [RFC7624] revelations efforts are underway to increase encryption of Internet traffic.
and the IETF consensus that "Pervasive Monitoring is an Attack" Applying confidentiality to transport header fields affects how
[RFC7258], efforts are underway to increase encryption of Internet protocol information is used [RFC8404], requiring consideration of
traffic. Applying confidentiality to transport header fields affects the trade-offs discussed in Section 2.3. To understand the
how protocol information is used [RFC8404], requiring consideration
of the trade-offs discussed in Section 2.3. To understand the
implications, it is necessary to understand how transport layer implications, it is necessary to understand how transport layer
headers are currently observed and/or modified by middleboxes within headers are currently observed and/or modified by middleboxes within
the network. the network.
We review some current uses in the following section. This does not This section reviews some current usage. This review does not
consider the intentional modification of transport headers by consider the intentional modification of transport headers by
middleboxes (such as in Network Address Translation, NAT, or middleboxes (such as in Network Address Translation, NAT, or
Firewalls). Common issues concerning IP address sharing are Firewalls). Common issues concerning IP address sharing are
described in [RFC6269]. described in [RFC6269].
3.1. Observing Transport Information in the Network 3.1. Observing Transport Information in the Network
If in-network observation of transport protocol headers is needed, If in-network observation of transport protocol headers is needed,
this requires knowledge of the format of the transport header: this requires knowledge of the format of the transport header:
o Flows need to be identified at the level required to perform the o Flows need to be identified at the level needed to perform the
observation; observation;
o The protocol and version of the header need to be visible, e.g., o The protocol and version of the header need to be visible, e.g.,
by defining the wire image [RFC8546]. As protocols evolve over by defining the wire image [RFC8546]. As protocols evolve over
time and there could be a need to introduce new transport headers. time and there could be a need to introduce new transport headers.
This could require interpretation of protocol version information This could require interpretation of protocol version information
or connection setup information; or connection setup information;
o The location and syntax of any observed transport headers need to o The location and syntax of any observed transport headers need to
be known. IETF transport protocols can specify this information. be known. IETF transport protocols can specify this information.
The following subsections describe various ways that observable The following subsections describe various ways that observable
transport information has been utilised. transport information has been utilised.
3.1.1. Flow Identification Using Transport Layer Headers 3.1.1. Flow Identification Using Transport Layer Headers
Flow identification is a common function. For example, performed by Flow/Session identification [RFC8558] is a common function. For
measurement activities, QoS classification, firewalls, Denial of example, performed by measurement activities, QoS classification,
Service, DOS, prevention. This becomes more complex and less easily firewalls, Denial of Service, DOS, prevention.
achieved when multiplexing is used at or above the transport layer.
Observable transport header information, together with information in Observable transport header information, together with information in
the network header, has been used to identify flows and their the network header, has been used to identify flows and their
connection state, together with the protocol options being used. connection state, together with the protocol options being used.
Transport protocols, such as TCP and the Stream Control Transport Transport protocols, such as TCP and the Stream Control Transport
Protocol (SCTP), specify a standard base header that includes Protocol (SCTP), specify a standard base header that includes
sequence number information and other data. They also have the sequence number information and other data. They also have the
possibility to negotiate additional headers at connection setup, possibility to negotiate additional headers at connection setup,
identified by an option number in the transport header. identified by an option number in the transport header.
In some uses, a low-numbered (well-known) transport port number can In some uses, a low-numbered (well-known) transport port number can
be used to identify the protocol, although port information alone is identify the protocol. However, port information alone is not
not sufficient to guarantee identification of a protocol since sufficient to guarantee identification when applications can use
applications can use arbitrary ports, multiple sessions can be arbitrary ports, multiple sessions can be multiplexed on a single
multiplexed on a single port, and ports can be re-used by subsequent port, and ports can be re-used by subsequent sessions. UDP-based
sessions. protocols often do not use well-known port numbers. Some flows can
instead be identified by observing signalling protocol data (e.g.,
UDP-based protocols often do not use well-known port numbers. Some [RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of magic
flows can instead be identified by observing signalling protocol data numbers placed in the first byte(s) of the datagram payload
(e.g., [RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of
magic numbers placed in the first byte(s) of the datagram payload
[RFC7983]. [RFC7983].
Concealing transport header information can remove information used Concealing transport header information can remove information used
to classify flows by passive observers along the path, so operators to classify flows by passive observers along the path, so operators
will be unable to use this information directly. Careful use of the will be unable to use this information directly. Operators could
network layer features can help address provide similar information turn to more ambitious ways to collect, estimate, or infer that data,
in the case where the network is unable to inspect transport protocol including heuristics based on the analysis of traffic patterns. For
headers. Operators could also turn to more ambitious ways to example, an operator that cannot access the Session Description
collect, estimate, or infer that data, including heuristics based on Protocol (SDP) session descriptions to classify a flow as audio
the analysis of traffic patterns. For example, an operator that no traffic, might instead use (possibly less-reliable) heuristics to
longer has access to Session Description Protocol (SDP) session infer that short UDP packets with regular spacing carry audio
descriptions to classify a flow carry as audio traffic might instead traffic. Operational practices aimed at inferring transport
use heuristics to infer that short UDP packets with regular spacing parameters are out of scope for this document, and are only mentioned
carry audio traffic. Operational practices aimed at inferring here to recognize that encryption does not prevent operators from
transport parameters are out of scope for this document, and are only attempting to apply practices that were used with unencrypted
mentioned here to recognize that encryption does not prevent transport headers.
operators from attempting to apply practices that were used with
unencrypted transport headers.
Confidentiality of the transport payload could be provided while
leaving some, or all, transport headers unencrypted, or providing
this information in a network-layer extension, possibly with
authentication. This provides many of the privacy and security
benefits while supporting operations and research, but at the cost of
ossifying the exposed headers.
3.1.2. Metrics derived from Transport Layer Headers 3.1.2. Metrics derived from Transport Layer Headers
Observable transport headers enable explicit 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 manage their at any point along the Internet path. Some operators use passive
portion of the Internet by characterizing the performance of link/ monitoring to manage their portion of the Internet by characterizing
network segments. Passive monitoring can observe traffic that does the performance of link/network segments. Inferences from transport
not encrypt the transport header information, and make inferences headers are used to derive performance metrics. A variety of open
from transport headers to derive performance metrics. source and commercial tools have been deployed that utilise transport
header information in this way to derive the following metrics:
A variety of open source and commercial tools have been deployed that
utilise transport header information in this way. The following
metrics can be derived:
Traffic Rate and Volume: Header information (e.g., sequence number Traffic Rate and Volume: Protocol sequence number and packet size
and packet size) allows derivation of volume measures per- can be used to derive volume measures per-application, to
application, to characterise the traffic that uses a network characterise the traffic that uses a network segment or the
segment or the pattern of network usage. This can be measured per pattern of network usage. Measurements can be per endpoint or for
endpoint or for an aggregate of endpoints (e.g., to assess an endpoint aggregate (e.g., to assess subscriber usage).
subscriber usage). It can also be used to trigger measurement- Measurments can also be used to trigger traffic shaping, and to
based traffic shaping, and to implement QoS support within the associate QoS support within the network and lower layers. Volume
network and lower layers. Volume measures can be valuable for measures can also be valuable for capacity planning and providing
capacity planning and providing detail of trends, rather than the detail of trends in usage.
volume per subscriber.
Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g., Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g.,
from transport sequence numbers) and has been used as a metric for from transport sequence numbers) and has been used as a metric for
performance assessment and to characterise transport behaviour. performance assessment and to characterise transport behaviour.
Understanding the location and root cause of loss can help an Understanding the location and root cause of loss can help an
operator determine whether this requires corrective action. operator determine whether this requires corrective action.
Network operators have used the variation in patterns of loss as a Network operators have used the variation in patterns of loss as a
key performance metric, utilising this to detect changes in the key performance metric, utilising this to detect changes in the
offered service. offered service.
There are various causes of loss, including corruption of link There are various causes of loss, including: corruption of link
frames (e.g., interference on a radio link), buffer overflow frames (e.g., due to interference on a radio link), buffering loss
(e.g., due to congestion), policing (traffic management), buffer (e.g., overflow due to congestion, Active Queue Management, AQM
management (e.g., Active Queue Management, AQM [RFC7567]), and [RFC7567], or inadequate provision following traffic pre-emption),
inadequate provision of traffic pre-emption. Understanding flow and policing (traffic management). Understanding flow loss rates
loss rates requires either observing sequence numbers in transport requires either observing sequence numbers in transport headers,
headers, or maintaining per-flow packet counters (but note that or maintaining per-flow packet counters (flow identification often
flow identification often requires transport header information). requires transport header information). Per-hop loss can also
Per-hop loss can be monitored at the interface level by devices in sometimes be monitored at the interface level by devices in the
the network. It is often valuable to understand the conditions network. It is often valuable to understand the conditions under
under which packet loss occurs. This usually requires relating which packet loss occurs, which usually requires relating loss to
per-flow loss to the traffic flowing on the network node/segment the traffic flowing on the network node/segment at the time of
at the time of loss. loss.
Observation of transport feedback information (e.g., RTP Control Observation of transport feedback information (e.g., RTP Control
Protocol (RTCP) reception reports [RFC3550], TCP SACK blocks) can Protocol (RTCP) reception reports [RFC3550], TCP SACK blocks) can
increase understanding of the impact of loss and help identify increase understanding of the impact of loss and help identify
cases where loss could have been wrongly identified, or where the cases where loss could have been wrongly identified, or where the
transport did not require the lost packet. It is sometimes more transport did not require transmission of the lost packet. It is
helpful to understand the pattern of loss, than the loss rate, sometimes more helpful to understand the pattern of loss, than the
because losses can often occur as bursts, rather than randomly- loss rate, because losses can often occur as bursts, rather than
timed events. randomly-timed events.
Throughput and Goodput: Throughput is the amount of data sent by a Throughput and Goodput: Throughput is the amount of data sent by a
flow per time interval. Goodput [RFC7928] is a measure of useful flow per time interval. Goodput [RFC7928] is a measure of useful
data exchanged (the ratio of useful data to total volume of data exchanged (the ratio of useful data to total volume of
traffic sent by a flow). The throughput achieved by a flow can be traffic sent by a flow). The throughput of a flow can be
determined even when transport header information is concealed, determined even when transport header information is concealed,
providing the individual flow can be identified. Goodput requires providing the individual flow can be identified. Goodput requires
ability to differentiate loss and retransmission of packets, for ability to differentiate loss and retransmission of packets, for
example by observing packet sequence numbers in the TCP or the example by observing packet sequence numbers in the TCP or the
Real-time Transport Protocol (RTP) headers [RFC3550]. Real-time Transport Protocol (RTP) headers [RFC3550].
Latency: Latency is a key performance metric that impacts Latency: Latency is a key performance metric that impacts
application and user-perceived response times. It often application and user-perceived response times. It often
indirectly impacts throughput and flow completion time. Latency 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 queuing in
network buffers has often been observed as a significant factor network buffers has often been observed as a significant factor
[bufferbloat]. Once the cause of unwanted latency has been [bufferbloat]. Once the cause of unwanted latency has been
identified, this can often be eliminated. identified, this can often be eliminated.
To measure latency across a part of a path, an observation point To measure latency across a part of a path, an observation point
[RFC7799] can measure the experienced round trip time (RTT) using [RFC7799] can measure the experienced round trip time (RTT) using
packet sequence numbers, and acknowledgements, or by observing packet sequence numbers, and acknowledgements, or by observing
header timestamp information. Such information allows an header timestamp information. Such information allows an
observation point in the network to determine not only the path observation point in the network to determine not only the path
RTT, but also to measure the upstream and downstream contribution RTT, but also allows measurement of the upstream and downstream
to the RTT. This could be used to locate a source of latency, contribution to the RTT. This could be used to locate a source of
e.g., by observing cases where the median RTT is much greater than latency, e.g., by observing cases where the median RTT is much
the minimum RTT for a part of a path. greater than the minimum RTT for a part of a path.
The service offered by network operators can benefit from latency The service offered by network operators can benefit from latency
information to understand the impact of configuration changes and information to understand the impact of configuration changes and
to tune deployed services. Latency metrics are key to evaluating to tune deployed services. Latency metrics are key to evaluating
and deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit and deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit
Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements
could identify excessively large buffers, indicating where to could identify excessively large buffers, indicating where to
deploy or configure AQM. An AQM method is often deployed in deploy or configure AQM. An AQM method is often deployed in
combination with other techniques, such as scheduling [RFC7567] combination with other techniques, such as scheduling [RFC7567]
[RFC8290] and although parameter-less methods are desired [RFC8290] and although parameter-less methods are desired
[RFC7567], current methods [RFC8290] [RFC8289] [RFC8033] often [RFC7567], current methods often require tuning [RFC8290]
cannot scale across all possible deployment scenarios. [RFC8289] [RFC8033] because they cannot scale across all possible
deployment scenarios.
Variation in delay: Some network applications are sensitive to Variation in delay: Some network applications are sensitive to
(small) changes in packet timing (jitter). Short and long-term (small) changes in packet timing (jitter). Short and long-term
delay variation can impact on the latency of a flow and hence the delay variation can impact on the latency of a flow and hence the
perceived quality of applications using the network. For example, perceived quality of applications using the network. For example,
jitter metrics are often cited when characterising paths jitter metrics are often cited when characterising paths
supporting real-time traffic. To assess the performance of such supporting real-time traffic. To assess the performance of such
applications, it can be necessary to measure the variation in applications, it can be necessary to measure the variation in
delay observed along a portion of the path [RFC3393] [RFC5481]. delay observed along a portion of the path [RFC3393] [RFC5481].
The requirements for observable transport headers resemble those The requirements for observable transport headers resemble those
skipping to change at page 13, line 18 skipping to change at page 15, line 6
have potential to simplify network equipment design as well as the have potential to simplify network equipment design as well as the
potential to improve robustness of the transport service. potential to improve robustness of the transport service.
Measurements of reordering can help understand the present level Measurements of reordering can help understand the present level
of reordering within deployed infrastructure, and inform decisions of reordering within deployed infrastructure, and inform decisions
about how to progress such mechanisms. Key performance indicators about how to progress such mechanisms. Key performance indicators
are retransmission rate, packet drop rate, sector utilisation are retransmission rate, packet drop rate, sector utilisation
level, a measure of reordering, peak rate, the ECN congestion level, a measure of reordering, peak rate, the ECN congestion
experienced (CE) marking rate, etc. experienced (CE) marking rate, etc.
Metrics have been defined that evaluate whether a network has Metrics have been defined that evaluate whether a network has
maintained packet order on a packet-by-packet basis [RFC4737] and maintained packet order on a packet-by-packet basis [RFC4737]
[RFC5236]. [RFC5236].
Techniques for measuring reordering typically observe packet Techniques for measuring reordering typically observe packet
sequence numbers. Some protocols provide in-built monitoring and sequence numbers. Some protocols provide in-built monitoring and
reporting functions. Transport fields in the RTP header [RFC3550] reporting functions. Transport fields in the RTP header [RFC3550]
[RFC4585] can be observed to derive traffic volume measurements [RFC4585] can be observed to derive traffic volume measurements
and provide information on the progress and quality of a session and provide information on the progress and quality of a session
using RTP. As with other measurement, metadata is often needed to using RTP. As with other measurement, metadata is often needed to
understand the context under which the data was collected, understand the context under which the data was collected,
including the time, observation point [RFC7799], and way in which including the time, observation point [RFC7799], and way in which
skipping to change at page 14, line 6 skipping to change at page 15, line 43
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 information.
Traffic that cannot be classified will typically receive a default Traffic that cannot be classified will typically receive a default
treatment. treatment.
Transport information can also be explicitly set in network-layer Transport information can also be explicitly set in network-layer
header fields that are not encrypted. This can provide information header fields that are not encrypted, serving as a replacement/
to enable a different forwarding treatment by the network, even when addition to the exposed transport information [RFC8558]. This can
a transport employs encryption to protect other header information. provide information to enable a different forwarding treatment by the
network, even when a transport employs encryption to 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 hide the presence and characteristics of these sub-flows. On want to hide the presence and characteristics of these sub-flows. On
the other hand, an encrypted transport could set the network-layer 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
network needs of individual sub-flows. There are several ways this network needs of individual sub-flows. There are several ways this
could be done: could be done:
IP Address: Applications expose the addresses used by endpoints, and IP Address: Applications normally expose the addresses used by
this is used in the forwarding decisions in network devices. endpoints, and this is used in the forwarding decisions in network
Address and other protocol information can be used by a Multi- devices. Address and other protocol information can be used by a
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], [RFC6437],
[RFC6438]) encourage endpoints to set the IPv6 Flow label field of [RFC6438]) encourage endpoints to set the IPv6 Flow label field of
the network-layer header. IPv6 "source nodes SHOULD assign each the network-layer header. IPv6 "source nodes SHOULD assign each
unrelated transport connection and application data stream to a unrelated transport connection and application data stream to a
new flow" [RFC6437]. A multiplexing transport could choose to use new flow" [RFC6437]. A multiplexing transport could choose to use
multiple Flow labels to allow the network to independently forward multiple Flow labels to allow the network to independently forward
subflows. RFC6437 provides further guidance on choosing a flow subflows. RFC6437 provides further guidance on choosing a flow
label value, stating these "should be chosen such that their bits label value, stating these "should be chosen such that their bits
exhibit a high degree of variability", and chosen so that "third exhibit a high degree of variability", and chosen so that "third
parties should be unlikely to be able to guess the next value that parties should be unlikely to be able to guess the next value that
a source of flow labels will choose". To promote privacy, the a source of flow labels will choose".
Flow Label assignment needs to avoid introducing linkability that
a network device may observe. Once set, a flow label can provide Once set, a flow label can provide information that can help
information that can help inform network-layer queuing and inform network-layer queuing and forwarding [RFC6438], for example
forwarding [RFC6438], for example with Equal Cost Multi-Path with Equal Cost Multi-Path routing and Link Aggregation [RFC6294].
routing and Link Aggregation [RFC6294]. Considerations when using Considerations when using IPsec are further described in
IPsec are further described in [RFC6438]. [RFC6438].
The choice of how to assign a Flow Label needs to avoid
introducing linkability that a network device could observe.
Inappropriate use by the transport can have privacy implications
(e.g., assigning the same label to two independent flows that
ought not to be classified the same).
Using the Network-Layer Differentiated Services Code Point: Using the Network-Layer Differentiated Services Code Point:
Applications can expose their delivery expectations to the network Applications can expose their delivery expectations to the network
by setting the Differentiated Services Code Point (DSCP) field of by setting the Differentiated Services Code Point (DSCP) field of
IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications
identify different forwarding treatments for individual sub-flows identify different forwarding treatments for individual sub-flows
(audio vs. video) based on the value of the DSCP field (audio vs. video) based on the value of the DSCP field
[I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information [I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information
to inform network-layer queuing and forwarding, rather than an to inform network-layer queuing and forwarding, rather than an
operator inferring traffic requirements from transport and operator inferring traffic requirements from transport and
application headers via a multi-field classifier. application headers via a multi-field classifier. Inappropriate
use can have privacy implications (e.g., assigning the same label
to two independent flows that ought not to be classified the
same). Inappropriate use by the transport can have privacy
implications (e.g., assigning a different DSCP to a subflow could
assist in a network device discovering the traffic pattern used by
an application). The field is mutable, i.e., some network devices
can be expected to change this field (use of each DSCP value is
defined by an RFC).
Since the DSCP value can impact the quality of experience for a Since the DSCP value can impact the quality of experience for a
flow, observations of service performance need to consider this flow, observations of service performance need to consider this
field when a network path has support for differentiated service field when a network path has support for differentiated service
treatment. treatment.
Using Explicit Congestion Marking: ECN [RFC3168] is a transport Using Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that utilises the ECN field in the network-layer header. mechanism that utilises the ECN field in the network-layer header.
Use of ECN explicitly informs the network-layer that a transport Use of ECN explicitly informs the network-layer that a transport
is ECN-capable, and requests ECN treatment of the flow. An ECN- is ECN-capable, and requests ECN treatment of the flow. An ECN-
skipping to change at page 15, line 36 skipping to change at page 17, line 40
AQM and ECN offer a range of algorithms and configuration options. AQM and ECN offer a range of algorithms and configuration options.
Tools therefore need to be available to network operators and Tools therefore need to be available to network operators and
researchers to understand the implication of configuration choices researchers to understand the implication of configuration choices
and transport behaviour as the use of ECN increases and new and transport behaviour as the use of ECN increases and new
methods emerge [RFC7567]. methods emerge [RFC7567].
When transport headers are concealed, operators will be unable to use When transport headers are concealed, operators will be unable to use
this information directly. Careful use of the network layer features this information directly. Careful use of the network layer features
can help address provide similar information in the case where the can help address provide similar information in the case where the
network is unable to inspect transport protocol headers. network is unable to inspect transport protocol headers.
Section Section 5 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
can view and analyse. For most packets, this has been the transport can view and analyse. For most packets, this has been the transport
layer, until the emergence of QUIC, with the obvious exception of layer, until the emergence of transport protocols performing header
Virtual Private Networks (VPNs) and IPsec. encryption, with the obvious exception of VPNs and IPsec.
When encryption conceals more layers in each packet, people seeking When encryption conceals more layers in each packet, people seeking
understanding of the network operation rely more on pattern inference understanding of the network operation rely more on pattern inference
and other heuristics. It remains to be seen whether more complex and other heuristics. It remains to be seen whether more complex
inferences can be mastered to produce the same monitoring accuracy inferences can be mastered to produce the same monitoring accuracy
(see section 2.1.1 of [RFC8404]). (see section 2.1.1 of [RFC8404]).
When measurement datasets are made available by servers or client When measurement datasets are made available by servers or client
endpoints, additional metadata, such as the state of the network, is endpoints, additional metadata, such as the state of the network, is
often required to interpret this data to answer questions about often necessary to interpret this data to answer questions about
network performance or understand a pathology. Collecting and network performance or understand a pathology. Collecting and
coordinating such metadata is more difficult when the observation coordinating such metadata is more difficult when the observation
point is at a different location to the bottleneck/device under point is at a different location to the bottleneck/device under
evaluation [RFC7799]. evaluation [RFC7799].
Packet sampling techniques are used to scale the processing involved Packet sampling techniques are used to scale the processing involved
in observing packets on high rate links. This exports only the in observing packets on high rate links. This exports only the
packet header information of (randomly) selected packets. The packet header information of (randomly) selected packets. The
utility of these measurements depends on the type of bearer and utility of these measurements depends on the type of bearer and
number of mechanisms used by network devices. Simple routers are number of mechanisms used by network devices. Simple routers are
skipping to change at page 16, line 47 skipping to change at page 19, line 7
Sometimes multiple on-path observation points are needed. By Sometimes multiple on-path observation points are needed. By
correlating observations of headers at multiple points along the path correlating observations of headers at multiple points along the path
(e.g., at the ingress and egress of a network segment), an observer (e.g., at the ingress and egress of a network segment), an observer
can determine the contribution of a portion of the path to an can determine the contribution of a portion of the path to an
observed metric, to locate a source of delay, jitter, loss, observed metric, to locate a source of delay, jitter, loss,
reordering, congestion marking, etc. reordering, congestion marking, etc.
3.2.2. Use by Operators to Plan and Provision Networks 3.2.2. Use by Operators to Plan and Provision Networks
Traffic measurements (e.g., traffic volume, loss, latency) are used Traffic measurements are used by operators to help plan deployment of
by operators to help plan deployment of new equipment and new equipment and configuration in their networks. Data is also
configuration in their networks. Data is also valuable to equipment valuable to equipment vendors who want to understand traffic trends
vendors who want to understand traffic trends and patterns of usage and patterns of usage as inputs to decisions about planning products
as inputs to decisions about planning products and provisioning for and provisioning for new deployments. This measurement information
new deployments. This measurement information can also be correlated can also be correlated with billing information when this is also
with billing information when this is also collected by an operator. collected by an operator.
A network operator supporting traffic that uses transport header A network operator supporting traffic that uses transport header
encryption might not have access to per-flow measurement data. encryption might not have access to per-flow measurement data.
Trends in aggregate traffic can be observed and can be related to the Trends in aggregate traffic can be observed and can be related to the
endpoint addresses being used, but it may be impossible to correlate endpoint addresses being used, but it might be impossible to
patterns in measurements with changes in transport protocols (e.g., correlate patterns in measurements with changes in transport
the impact of changes in introducing a new transport protocol protocols (e.g., the impact of changes in introducing a new transport
mechanism). This increases the dependency on other indirect sources protocol mechanism). This increases the dependency on other indirect
of information to inform planning and provisioning. sources of information to inform planning and provisioning.
3.2.3. Service Performance Measurement 3.2.3. Service Performance Measurement
Traffic measurements (e.g., traffic volume, loss, latency) can be Traffic measurements (e.g., traffic volume, loss, latency) can be
used by various actors to help analyse the performance offered to the used by various actors to help analyse the performance offered to the
users of a network segment, and to inform operational practice. users of a network segment, and to inform operational practice.
While active measurements (see section 3.4 of [RFC7799]) may be used While active measurements (see section 3.4 of [RFC7799]) could be
within a network, passive measurements (see section 3.6 of [RFC7799]) used within a network, passive measurements (see section 3.6 of
can have advantages in terms of eliminating unproductive test [RFC7799]) can have advantages in terms of eliminating unproductive
traffic, reducing the influence of test traffic on the overall test traffic, reducing the influence of test traffic on the overall
traffic mix, and the ability to choose the point of observation (see traffic mix, and the ability to choose the point of observation (see
Section 3.2.1). However, passive measurements can rely on observing Section 3.2.1). Passive measurements can rely on observing transport
transport headers which is not possible if those headers are headers, which is not possible if those headers are encrypted, but
encrypted. could utilise information about traffic volumes or patterns of
interaction to deduce metrics.
3.2.4. Measuring Transport to Support Network Operations 3.2.4. Measuring Transport to Support Network Operations
Information provided by tools observing transport headers can help Information provided by tools observing transport headers can help
determine whether mechanisms are needed in the network to prevent determine whether mechanisms are needed in the network to prevent
flows from acquiring excessive network capacity. Operators can flows from acquiring excessive network capacity. Operators can
implement operational practices to manage traffic flows (e.g., to implement operational practices to manage traffic flows (e.g., under
prevent flows from acquiring excessive network capacity under severe severe congestion) by deploying rate-limiters, traffic shaping or
congestion) by deploying rate-limiters, traffic shaping or network network transport circuit breakers [RFC8084].
transport circuit breakers [RFC8084].
Congestion Control Compliance of Traffic: Congestion control is a Congestion Control Compliance of Traffic: Congestion control is a
key transport function [RFC2914]. Many network operators key transport function [RFC2914]. Many network operators
implicitly accept that TCP traffic complies with a behaviour that implicitly accept that TCP traffic complies with a behaviour that
is acceptable for use in the shared Internet. TCP algorithms have is acceptable for use in the shared Internet. TCP algorithms have
been continuously improved over decades and they have reached a been continuously improved over decades and they have reached a
level of efficiency and correctness that custom application-layer level of efficiency and correctness that custom application-layer
mechanisms will struggle to easily duplicate [RFC8085]. mechanisms will struggle to easily duplicate [RFC8085].
A standards-compliant TCP stack provides congestion control that A standards-compliant TCP stack provides congestion control that
may therefore be judged safe for use across the Internet. is judged safe for use across the Internet. Applications
Applications developed on top of well-designed transports can be developed on top of well-designed transports can be expected to
expected to appropriately control their network usage, reacting appropriately control their network usage, reacting when the
when the network experiences congestion, by back-off and reduce network experiences congestion, by back-off and reduce the load
the load placed on the network. This is the normal expected placed on the network. This is the normal expected behaviour for
behaviour for IETF-specified transport (e.g., TCP and SCTP). IETF-specified transports (e.g., TCP and SCTP).
However, when anomalies are detected, tools can interpret the However, when anomalies are detected, tools can interpret the
transport protocol header information to help understand the transport protocol header information to help understand the
impact of specific transport protocols (or protocol mechanisms) on impact of specific transport protocols (or protocol mechanisms) on
the other traffic that shares a network. An observation in the the other traffic that shares a network. An observation in the
network can gain an understanding of the dynamics of a flow and network can gain an understanding of the dynamics of a flow and
its congestion control behaviour. Analysing observed flows can its congestion control behaviour. Analysing observed flows can
help to build confidence that an application flow backs-off its help to build confidence that an application flow backs-off its
share of the network load in the face of persistent congestion, share of the network load in the face of persistent congestion,
and hence to understand whether the behaviour is appropriate for and hence to understand whether the behaviour is appropriate for
sharing limited network capacity. For example, it is common to sharing limited network capacity. For example, it is common to
visualise plots of TCP sequence numbers versus time for a flow to visualise plots of TCP sequence numbers versus time for a flow to
understand how a flow shares available capacity, deduce its understand how a flow shares available capacity, deduce its
dynamics in response to congestion, etc. dynamics in response to congestion, etc.
The ability to identify sources that contribute to persistent The ability to identify sources that contribute to persistent
congestion is important to safe operation of network congestion is important to the safe operation of network
infrastructure, and mechanisms can inform configuration of network infrastructure, and can inform configuration of network devices to
devices to complement the endpoint congestion avoidance mechanisms complement the endpoint congestion avoidance mechanisms [RFC7567]
[RFC7567] [RFC8084] to avoid a portion of the network being driven [RFC8084] to avoid a portion of the network being driven into
into congestion collapse [RFC2914]. congestion collapse [RFC2914].
Congestion Control Compliance for UDP traffic: UDP provides a Congestion Control Compliance for UDP traffic: UDP provides a
minimal message-passing datagram transport that has no inherent minimal message-passing datagram transport that has no inherent
congestion control mechanisms. Because congestion control is congestion control mechanisms. Because congestion control is
critical to the stable operation of the Internet, applications and critical to the stable operation of the Internet, applications and
other protocols that choose to use UDP as a transport are required other protocols that choose to use UDP as a transport need to
to employ mechanisms to prevent congestion collapse, avoid employ mechanisms to prevent collapse, avoid unacceptable
unacceptable contributions to jitter/latency, and to establish an contributions to jitter/latency, and to establish an acceptable
acceptable share of capacity with concurrent traffic [RFC8085]. share of capacity with concurrent traffic [RFC8085].
A network operator needs tools to understand if datagram flows A network operator needs tools to understand if datagram flows
(e.g., using UDP) comply with congestion control expectations and (e.g., using UDP) comply with congestion control expectations and
therefore whether there is a need to deploy methods such as rate- therefore whether there is a need to deploy methods such as rate-
limiters, transport circuit breakers, or other methods to enforce limiters, transport circuit breakers, or other methods to enforce
acceptable usage for the offered service. acceptable usage for the offered service.
UDP flows that expose a well-known header by specifying the format UDP flows that expose a well-known header by specifying the format
of header fields can allow information to be observed to gain of header fields can allow information to be observed to gain
understanding of the dynamics of a flow and its congestion control understanding of the dynamics of a flow and its congestion control
skipping to change at page 19, line 16 skipping to change at page 21, line 23
3.3. Use for Network Diagnostics and Troubleshooting 3.3. Use for Network Diagnostics and Troubleshooting
Transport header information can be useful for a variety of Transport header information can be useful for a variety of
operational tasks [RFC8404]: to diagnose network problems, assess operational tasks [RFC8404]: to diagnose network problems, assess
network provider performance, evaluate equipment/protocol network provider performance, evaluate equipment/protocol
performance, capacity planning, management of security threats performance, capacity planning, management of security threats
(including denial of service), and responding to user performance (including denial of service), and responding to user performance
questions. Section 3.1.2 and Section 5 of [RFC8404] provide further questions. Section 3.1.2 and Section 5 of [RFC8404] provide further
examples. These tasks seldom involve the need to determine the examples. These tasks seldom involve the need to determine the
contents of the transport payload, or other application details. contents of the transport payload, or other application details. The
use of payload encryption has the desirable effect of preventing
unintended observation of the user data.
A network operator supporting traffic that uses transport header A network operator supporting traffic that uses transport header
encryption can see only encrypted transport headers. This prevents encryption can see only encrypted transport headers. This prevents
deployment of performance measurement tools that rely on transport deployment of performance measurement tools that rely on transport
protocol information. Choosing to encrypt all the information protocol information. Choosing to encrypt all the information
reduces the ability of an operator to observe transport performance reduces the ability of an operator to observe transport performance
and could limit the ability of network operators to trace problems, and could limit the ability of network operators to trace problems,
make appropriate QoS decisions, or response to other queries about make appropriate QoS decisions, or response to other queries about
the network service. For some this will be blessing, for others it the network service. For some this will be blessing, for others it
may be a curse. For example, operational performance data about might be a curse. For example, operational performance data about
encrypted flows needs to be determined by traffic pattern analysis, encrypted flows needs to be determined by traffic pattern analysis,
rather than relying on traditional tools. This can impact the rather than relying on traditional tools. This can impact the
ability of the operator to respond to faults, it could require ability of the operator to respond to faults, it could require
reliance on endpoint diagnostic tools or user involvement in reliance on endpoint diagnostic tools or user involvement in
diagnosing and troubleshooting unusual use cases or non-trivial diagnosing and troubleshooting unusual use cases or non-trivial
problems. A key need here is for tools to provide useful information problems. A key need here is for tools to provide useful information
during network anomalies (e.g., significant reordering, high or during network anomalies (e.g., significant reordering, high or
intermittent loss). intermittent loss).
Measurements can be used to monitor the health of a portion of the Measurements can be used to monitor the health of a portion of the
skipping to change at page 20, line 46 skipping to change at page 23, line 7
compression has been specified for use with TCP/IP and RTP/UDP/IP compression has been specified for use with TCP/IP and RTP/UDP/IP
flows [RFC2507], [RFC2508], [RFC4995]. flows [RFC2507], [RFC2508], [RFC4995].
While it is possible to compress only the network layer headers, While it is possible to compress only the network layer headers,
significant savings can be made if both the network and transport significant savings can be made if both the network and transport
layer headers are compressed together as a single unit. The Secure layer headers are compressed together as a single unit. The Secure
RTP extensions [RFC3711] were explicitly designed to leave the RTP extensions [RFC3711] were explicitly designed to leave the
transport protocol headers unencrypted, but authenticated, since transport protocol headers unencrypted, but authenticated, since
support for header compression was considered important. Encrypting support for header compression was considered important. Encrypting
the transport protocol headers does not break such header the transport protocol headers does not break such header
compression, but does cause it to fall back to compressing only the compression, but does cause a fall back to compressing only the
network layer headers, with a significant reduction in efficiency. network layer headers, with a significant reduction in efficiency.
This can impact the efficiency of a link/path.
4. Encryption and Authentication of Transport Headers 4. Encryption and Authentication of Transport Headers
End-to-end encryption can be applied at various protocol layers. It End-to-end encryption can be applied at various protocol layers. It
can be applied above the transport to encrypt the transport payload. can be applied above the transport to encrypt the transport payload
Encryption methods can hide information from an eavesdropper in the (e.g., using TLS). This can hide information from an eavesdropper in
network. Encryption 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. Neither an hiding data relating to user/device identity or location.
integrity check nor encryption methods prevent traffic analysis, and
usage needs to reflect that profiling of users, identification of
location and fingerprinting of behaviour can take place even on
encrypted traffic flows. Any header information that has a clear
definition in the protocol's message format(s), or is implied by that
definition, and is not cryptographically confidentiality-protected
can be unambiguously interpreted by on-path observers [RFC8546].
There are several motivations for encryption: There are several motivations for encryption:
o One motive to use encryption is a response to perceptions that the o One motive to use encryption is a response to perceptions that the
network has become ossified by over-reliance on middleboxes that network has become ossified by over-reliance on middleboxes that
prevent new protocols and mechanisms from being deployed. This prevent new protocols and mechanisms from being deployed. This
has lead to a perception that there is too much "manipulation" of has lead to a perception that there is too much "manipulation" of
protocol headers within the network, and that designing to deploy protocol headers within the network, and that designing to deploy
in such networks is preventing transport evolution. In the light in such networks is preventing transport evolution. In the light
of this, a method that authenticates transport headers could help of this, a method that authenticates transport headers could help
skipping to change at page 21, line 43 skipping to change at page 23, line 41
particular middleboxes that are deliberately deployed to realise a particular middleboxes that are deliberately deployed to realise a
useful function for the network and/or users[RFC3135]. useful function for the network and/or users[RFC3135].
o Another motivation stems from increased concerns about privacy and o Another motivation stems from increased concerns about privacy and
surveillance. Some Internet users have valued the ability to surveillance. Some Internet users have valued the ability to
protect identity, user location, and defend against traffic protect identity, user location, and defend against traffic
analysis, and have used methods such as IPsec Encapsulated analysis, and have used methods such as IPsec Encapsulated
Security Payload (ESP), VPNs and other encrypted tunnel Security Payload (ESP), VPNs and other encrypted tunnel
technologies. Revelations about the use of pervasive surveillance technologies. Revelations about the use of pervasive surveillance
[RFC7624] have, to some extent, eroded trust in the service [RFC7624] have, to some extent, eroded trust in the service
offered by network operators, and following the Snowden revelation offered by network operators, and following the Snowden
in the USA in 2013 has led to an increased desire for people to revelations in the USA in 2013 has led to an increased desire for
employ encryption to avoid unwanted "eavesdropping" on their people to employ encryption to avoid unwanted "eavesdropping" on
communications. Concerns have also been voiced about the addition their communications. Concerns have also been voiced about the
of information to packets by third parties to provide analytics, addition of information to packets by third parties to provide
customization, advertising, cross-site tracking of users, to bill analytics, customization, advertising, cross-site tracking of
the customer, or to selectively allow or block content. Whatever users, to bill the customer, or to selectively allow or block
the reasons, there are now activities in the IETF to design new content. Whatever the reasons, the IETF is designing new
protocols that could include some form of transport header protocols that include transport header encryption (e.g., QUIC
encryption (e.g., QUIC [I-D.ietf-quic-transport]) to supplement [I-D.ietf-quic-transport]) to supplement the already widespread
the already widespread payload encryption. payload encryption.
Authentication methods that provide integrity checks of protocols o Any header information that has a clear definition in the protocol
fields have also been specified at the network layer, and this also message format(s), or is implied by that definition, and is not
protects transport header fields. The network layer itself carries cryptographically confidentiality-protected can be unambiguously
protocol header fields that are increasingly used to help forwarding interpreted by on-path observers [RFC8546].
decisions reflect the need of transport protocols, such as the IPv6
Flow Label [RFC6437], DSCP, and ECN fields.
The use of transport layer authentication and encryption exposes a Encryption methods do not prevent traffic analysis, and usage needs
tussle between middlebox vendors, operators, applications developers to reflect that profiling of users, identification of location, and
and users: fingerprinting of behaviour can take place even on encrypted traffic
flows. The use of transport layer authentication and encryption
exposes a tussle between middlebox vendors, operators, applications
developers and users:
o On the one hand, future Internet protocols that enable large-scale o On the one hand, future Internet protocols that enable large-scale
encryption assist in the restoration of the end-to-end nature of encryption assist in the restoration of the end-to-end nature of
the Internet by returning complex processing to the endpoints, the Internet by returning complex processing to the endpoints,
since middleboxes cannot modify what they cannot see. since middleboxes cannot modify what they cannot see.
o On the other hand, encryption of transport layer header o On the other hand, encryption of transport layer header
information has implications for people who are responsible for information has implications for people who are responsible for
operating networks and researchers and analysts seeking to operating networks and researchers and analysts seeking to
understand the dynamics of protocols and traffic patterns. understand the dynamics of protocols and traffic patterns.
skipping to change at page 23, line 6 skipping to change at page 25, line 4
expose the transport protocol header information in the clear, expose the transport protocol header information in the clear,
allows in-network devices to observe these fields. An integrity allows in-network devices to observe these fields. An integrity
check is not able to prevent in-network modification, but can check is not able to prevent in-network modification, but can
prevent a receiving from accepting changes and avoid impact on the prevent a receiving from accepting changes and avoid impact on the
transport protocol operation. transport protocol operation.
An example transport authentication mechanism is TCP- An example transport authentication mechanism is TCP-
Authentication (TCP-AO) [RFC5925]. This TCP option authenticates Authentication (TCP-AO) [RFC5925]. This TCP option authenticates
the IP pseudo header, TCP header, and TCP data. TCP-AO protects the IP pseudo header, TCP header, and TCP data. TCP-AO protects
the transport layer, preventing attacks from disabling the TCP the transport layer, preventing attacks from disabling the TCP
connection itself and provides replay protection. TCP-AO may connection itself and provides replay protection. TCP-AO 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 Greasing: Protocols often provide extensibility features, reserving
skipping to change at page 23, line 34 skipping to change at page 25, line 32
field value. field value.
A protocol can intentionally vary the value, format, and/or A protocol can intentionally vary the value, format, and/or
presence of observable transport header fields. This behaviour, presence of observable transport header fields. This behaviour,
known as GREASE (Generate Random Extensions And Sustain known as GREASE (Generate Random Extensions And Sustain
Extensibility) is designed to avoid a network device ossifying the Extensibility) is designed to avoid a network device ossifying the
use of a specific observable field. Greasing seeks to ease use of a specific observable field. Greasing seeks to ease
deployment of new methods. It can also prevent in-network devices deployment of new methods. It can also prevent in-network devices
utilising the information in a transport header, or can make an utilising the information in a transport header, or can make an
observation robust to a set of changing values, rather than a observation robust to a set of changing values, rather than a
specific set of values. specific set of values
Encrypting the Transport Payload: The transport layer payload can be
encrypted to protect the content of transport segments. This
leaves transport protocol header information in the clear. The
integrity of immutable transport header fields could be protected
by combining this with an integrity check.
Examples of encrypting the payload include Transport Layer
Security (TLS) over TCP [RFC8446] [RFC7525], Datagram TLS (DTLS)
over UDP [RFC6347] [RFC7525], Secure RTP [RFC3711], and TCPcrypt
[RFC8548] which permits opportunistic encryption of the TCP
transport payload.
Encrypting the Transport Headers and Payload: The network layer
payload could be encrypted (including the entire transport header
and the payload). This method provides confidentiality of the
entire transport packet. It therefore does not expose any
transport information to devices in the network, which also
prevents modification along a network path.
One example of encryption at the network layer is the use of IPsec
Encapsulating Security Payload (ESP) [RFC4303] in tunnel mode.
This encrypts and authenticates all transport headers, preventing
visibility of the transport headers by in-network devices. Some
VPN methods also encrypt these headers.
Selectively Encrypting Transport Headers and Payload: A transport Selectively Encrypting Transport Headers and Payload: A transport
protocol design can encrypt selected header fields, while also protocol design can encrypt selected header fields, while also
choosing to authenticate the entire transport header. This allows choosing to authenticate the entire transport header. This allows
specific transport header fields to be made observable by network specific transport header fields to be made observable by network
devices. End-to end integrity checks can prevent an endpoint from devices. End-to end integrity checks can prevent an endpoint from
undetected modification of the immutable transport headers. undetected modification of the immutable transport headers.
Mutable fields in the transport header provide opportunities for Mutable fields in the transport header provide opportunities for
middleboxes to modify the transport behaviour (e.g., the extended middleboxes to modify the transport behaviour (e.g., the extended
headers described in [I-D.trammell-plus-abstract-mech]). This headers described in [I-D.trammell-plus-abstract-mech]). This
considers only immutable fields in the transport headers, that is, considers only immutable fields in the transport headers, that is,
fields that can be authenticated End-to-End across a path. 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. 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 required to use variable format management decisions that are needed to use variable format
fields. Instead, fields of a specific type ought to always be fields. Instead, fields of a specific type ought to always be
sent with the same level of confidentiality or integrity sent with the same level of confidentiality or integrity
protection. protection.
As seen, different transports use encryption to protect their header As seen, different transports use encryption to protect their header
information to varying degrees. There is, however, a trend towards information to varying degrees. There is, however, a trend towards
increased protection with newer transport protocols. increased protection with newer transport protocols.
5. Addition of Transport Information to Network-Layer Protocol Headers 5. Addition of Transport Information to Network-Layer Headers
An on-path device can make measurements by appending 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 to packets at the ingress to a maintenance domain (OAM) information in an additional packet header. Using network-
layer approaches to reveal information has the potential that the
same method (and hence same observation and analysis tools) can be
consistently used by multiple transport protocols [RFC8558]. There
could also be less desirable implications of separating the operation
of the transport protocol from the measurement framework.
5.1. Use of OAM within a Maintenance Domain
OAM information can be added at the ingress to a maintenance domain
(e.g., an Ethernet protocol header with timestamps and sequence (e.g., an Ethernet protocol header with timestamps and sequence
number information using a method such as 802.11ag or in-situ OAM number information using a method such as 802.11ag or in-situ OAM
[I-D.ietf-ippm-ioam-data]) and removing the additional header at the [I-D.ietf-ippm-ioam-data], or as a part of encapsulation protocol).
egress of the maintenance domain. This approach enables some types The additional header information is typically removed the at the
of measurements, but does not cover the entire range of measurements egress of the maintenance domain.
described in this document. In some cases, it can be difficult to
position measurement tools at the required segments/nodes and there
can be challenges in correlating the downsream/upstream information
when in-band OAM data is inserted by an on-path device. This has the
advantage that a single header can support all transport protocols,
but there could also be less desirable implications of separating the
operation of the transport protocol from the measurement framework.
Another example of a network-layer approach is the IPv6 Performance Although some types of measurements are supported, this approach does
and Diagnostic Metrics (PDM) Destination Option [RFC8250]. This not cover the entire range of measurements described in this
allows a sender to optionally include a destination option that document. In some cases, it can be difficult to position measurement
caries header fields that can be used to observe timestamps and tools at the appropriate segments/nodes and there can be challenges
packet sequence numbers. This information could be authenticated by in correlating the downstream/upstream information when in-band OAM
receiving transport endpoints when the information is added at the data is inserted by an on-path device.
sender and visible at the receiving endpoint, although methods to do
this have not currently been proposed. This method needs to be
explicitly enabled at the sender.
Current measurement results suggest that it can be undesirable to 5.2. Use of OAM across Multiple Maintenance Domains
rely on methods requiring end to end support of network options or
extension headers across the Internet. IPv4 network options are OAM information can also be added at the network layer as an IPv6
often not supported (or are carried on a slower processing path) and extension header or an IPv4 option. This information can be used
some IPv6 networks have been observed to drop packets that set an across multiple network segments, or between the transport endpoints.
IPv6 header extension (e.g., results from 2016 in [RFC7872]).
Another possibility is that protocols that separately expose header One example is the IPv6 Performance and Diagnostic Metrics (PDM)
information do not necessarily have an incentive to expose the actual Destination Option [RFC8250]. This allows a sender to optionally
information that is utilised by the protocol itself and could include a destination option that caries header fields that can be
used to observe timestamps and packet sequence numbers. This
information could be authenticated by receiving transport endpoints
when the information is added at the sender and visible at the
receiving endpoint, although methods to do this have not currently
been proposed. This method needs to be explicitly enabled at the
sender.
Current measurement results suggest that it could currently be
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]).
Another potential issue is that protocols that separately expose
header information do not necessarily have an incentive to expose the
actual information that is utilised by the protocol itself and could
therefore manipulate the exposed header information to gain an therefore manipulate the exposed header information to gain an
advantage from the network. The incentive to reflect actual advantage from the network. Where the information is provided by an
transport information needs to be considered when proposing a method endpoint, the incentive to reflect actual transport information needs
that selectively exposes header information. to be considered when proposing a method.
6. Implications of Protecting the Transport Headers 6. Implications of Protecting the Transport Headers
The choice of which fields to expose and which to encrypt is a design The choice of which fields to expose and which to encrypt is a design
choice for the transport protocol. Any selective encryption method choice for the transport protocol. Any selective encryption method
requires trading two conflicting goals for a transport protocol requires trading two conflicting goals for a transport protocol
designer to decide which header fields to encrypt. Security work designer to decide which header fields to encrypt. Security work
typically employs a design technique that seeks to expose only what typically employs a design technique that seeks to expose only what
is needed. This approach provides incentives to not reveal any is needed. This approach provides incentives to not reveal any
information that is not necessary for the end-to-end communication. information that is not necessary for the end-to-end communication.
skipping to change at page 26, line 13 skipping to change at page 27, line 49
transport protocols. transport protocols.
6.1. Independent Measurement 6.1. Independent Measurement
Independent observation by multiple actors is important if the Independent observation by multiple actors is important if the
transport community is to maintain an accurate understanding of the transport community is to maintain an accurate understanding of the
network. Encrypting transport header encryption changes the ability network. Encrypting transport header encryption changes the ability
to collect and independently analyse data. Internet transport to collect and independently analyse data. Internet transport
protocols employ a set of mechanisms. Some of these need to work in protocols employ a set of mechanisms. Some of these need to work in
cooperation with the network layer for loss detection and recovery, cooperation with the network layer for loss detection and recovery,
congestion detection and congestion control. Others need to work congestion detection and control. Others need to work only end-to-
only end-to-end (e.g., parameter negotiation, flow-control). end (e.g., parameter negotiation, flow-control).
The majority of present Internet applications use two well-known The majority of present Internet applications use two well-known
transport protocols, TCP and UDP. Although TCP represents the transport protocols, TCP and UDP. Although TCP represents the
majority of current traffic, many real-time applications use UDP, and majority of current traffic, many real-time applications use UDP, and
much of this traffic utilises RTP format headers in the payload of much of this traffic utilises RTP format headers in the payload of
the UDP datagram. Since these protocol headers have been fixed for the UDP datagram. Since these protocol headers have been fixed for
decades, a range of tools and analysis methods have became common and decades, a range of tools and analysis methods have became common and
well-understood. well-understood.
Protocols that expose the state information used by the transport Protocols that expose the state information used by the transport
skipping to change at page 26, line 36 skipping to change at page 28, line 25
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 header information that can be used for
measurement at any point along the path. This information is measurement at any point along the path. This information is
necessary for the protocol's correct operation, therefore there is no necessary for the protocol's correct operation, therefore there is no
incentive for a TCP implementation to put incorrect information in incentive for a TCP or RTP implementation to put incorrect
this transport header. A network device can have confidence that the information in this transport header. A network device can have
well-known (and ossified) transport information represents the actual confidence that the well-known (and ossified) transport information
state of the endpoints. represents the actual state of the endpoints.
When encryption is used to conceal some or all of the transport When encryption is used to conceal some or all of the transport
headers, the transport protocol choose what information to reveal to headers, the transport protocol chooses which information to reveal
the network about its internal state, what information to leave to the 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, for example, to
provide summary data regarding its performance, congestion control provide summary data regarding its performance, congestion control
state, etc., or to make an explicit measurement signal available. state, etc., or to make an explicit measurement signal available.
For example, a QUIC endpoint could set the spin bit to reflect to For example, a QUIC endpoint can optionally set the spin bit to
explicitly reveal a session's RTT [I-D.ietf-quic-spin-exp]). reflect to explicitly reveal the RTT of an encrypted transport
session to the on-path network devices [I-D.ietf-quic-transport]).
When providing or using such information, it becomes important to When providing or using such information, it becomes important to
consider the privacy of the user and their incentive for providing consider the privacy of the user and their incentive for providing
accurate and detailed information. Protocols that selectively reveal accurate and detailed information. Protocols that selectively reveal
some transport state or measurement signals are choosing to establish some transport state or measurement signals are choosing to establish
a trust relationship with the network operators. There is no a trust relationship with the network operators. There is no
protocol mechanism that can guarantee that the information provided protocol mechanism that can guarantee that the information provided
represents the actual transport state of the endpoints, since those represents the actual transport state of the endpoints, since those
endpoints can always send additional information in the encrypted endpoints can always send additional information in the encrypted
part of the header, to update or replace whatever they reveal. This part of the header, to update or replace whatever they reveal. This
reduces the ability to independently measure and verify that a reduces the ability to independently measure and verify that a
protocol is behaving as expected. Some operational uses need the protocol is behaving as expected. Some operational uses need the
information to contain sufficient detail to understand, and possibly information to contain sufficient detail to understand, and possibly
reconstruct, the network traffic pattern for further testing; such reconstruct, the network traffic pattern for further testing; such
operators must gain the trust of transport protocol implementers if operators need to gain the trust of transport protocol implementers
they are to correctly reveal such information. if they are to correctly reveal such information.
OAM data records [I-D.ietf-ippm-ioam-data] could be embedded into a Operations, Administration, and Maintenance (OAM) data records
variety of encapsulation methods at different layers to support the [I-D.ietf-ippm-ioam-data] could be embedded into a variety of
goals of a specific operational domain. OAM-related metadata can encapsulation methods at different layers to support the goals of a
support functions such as performance evaluation, path-tracing, path specific operational domain. OAM-related metadata can support
functions such as performance evaluation, path-tracing, path
verification information, classification and a diversity of other verification information, classification and a diversity of other
uses. When encryption is used to conceal some or all of the uses. When encryption is used to conceal some or all of the
transport headers, analysis will require coordination between actors transport headers, analysis will require coordination between actors
at different layers to successfully characterise flows and correlate at different layers to successfully characterise flows and correlate
the performance or behaviour of a specific mechanism with the the performance or behaviour of a specific mechanism with the
configuration and traffic using operational equipment (e.g., configuration and traffic using operational equipment (e.g.,
combining transport and network measurements to explore congestion combining transport and network measurements to explore congestion
control dynamics, the implications of designs for active queue control dynamics, the implications of designs for active queue
management or circuit breakers). management or circuit breakers).
For some usage a standardised endpoint-based logging format (e.g., Some measurements could be completed by utilising a standardised
based on Quic-Trace [Quic-Trace]) could offer an alternative for some endpoint-based logging format (e.g., based on Quic-Trace
in-network measurement. Such information will have a diversity of [Quic-Trace]). Such information will have a diversity of uses,
uses, including developers wishing to debug/understand the transport/ including developers wishing to debug/understand the transport/
application protocols with which they work, researchers seeking to application protocols with which they work, researchers seeking to
spot trends and anomalies, and to characterise variants of protocols. spot trends and anomalies, and to characterise variants of protocols.
Measurments based on logging will need to establish the validity and Logs collected at endpoints could be shared (after appropriate
annoymisation) to help understand performance and pathologies.
Measurements based on logging will need to establish the validity and
provenance of the logged information to establish how and when traces provenance of the logged information to establish how and when traces
were captured. were captured.
However, endpoint logs do not provide equivalent information to in- However, endpoint logs do not provide equivalent information to in-
network measurements. In particular, endpoint logs contain only a network measurements. In particular, endpoint logs contain only a
part of the information needed to understand the operation of network part of the information needed to understand the operation of network
devices and identify issues such as link performance or capacity devices and identify issues such as link performance or capacity
sharing between multiple flows. Additional information is needed to sharing between multiple flows. Additional information is needed to
determine which equipment/links are used and the configuration of determine which equipment/links are used and the configuration of
equipment along the network paths being measured. equipment along the network paths being measured.
6.2. Characterising "Unknown" Network Traffic 6.2. Characterising "Unknown" Network Traffic
The patterns and types of traffic that share Internet capacity change The patterns and types of traffic that share Internet capacity change
over time as networked applications, usage patterns and protocols over time as networked applications, usage patterns and protocols
continue to evolve. continue to evolve.
If "unknown" or "uncharacterised" traffic patterns form a small part If "unknown" or "uncharacterised" traffic patterns form a small part
of the traffic aggregate passing through a network device or segment of the traffic aggregate passing through a network device or segment
of the network the path, the dynamics of the uncharacterised traffic of the network the path, the dynamics of the uncharacterised traffic
may not have a significant collateral impact on the performance of might not have a significant collateral impact on the performance of
other traffic that shares this network segment. Once the proportion other traffic that shares this network segment. Once the proportion
of this traffic increases, the need to monitor the traffic and of this traffic increases, the need to monitor the traffic and
determine if appropriate safety measures need to be put in place. determine if appropriate safety measures need to be put in place.
Tracking the impact of new mechanisms and protocols requires traffic Tracking the impact of new mechanisms and protocols requires traffic
volume to be measured and new transport behaviours to be identified. volume to be measured and new transport behaviours to be identified.
This is especially true of protocols operating over a UDP substrate. This is especially true of protocols operating over a UDP substrate.
The level and style of encryption needs to be considered in The level and style of encryption needs to be considered in
determining how this activity is performed. On a shorter timescale, determining how this activity is performed. On a shorter timescale,
information may also need to be collected to manage denial of service information could also need to be collected to manage denial of
attacks against the infrastructure. service attacks against the infrastructure.
6.3. Accountability and Internet Transport Protocols 6.3. Accountability and Internet Transport Protocols
Information provided by tools observing transport headers can be used Information provided by tools observing transport headers can be used
to classify traffic, and to limit the network capacity used by to classify traffic, and to limit the network capacity used by
certain flows, as discussed in Section 3.2.4). Equally, operators certain flows, as discussed in Section 3.2.4). Equally, operators
could use analysis of transport headers and transport flow state to could use analysis of transport headers and transport flow state to
demonstrate that they are not providing differential treatment to demonstrate that they are not providing differential treatment to
certain flows. Obfuscating or hiding this information using certain flows. Obfuscating or hiding this information using
encryption may lead operators and maintainers of middleboxes encryption could lead operators and maintainers of middleboxes
(firewalls, etc.) to seek other methods to classify, and potentially (firewalls, etc.) to seek other methods to classify, and potentially
other mechanisms to condition, network traffic. other mechanisms to condition, network traffic.
A lack of data that reduces the level of precision with which flows A lack of data that reduces the level of precision with which flows
can be classified also reduces the design space for conditioning can be classified also reduces the design space for conditioning
mechanisms (e.g., rate limiting, circuit breaker techniques mechanisms (e.g., rate limiting, circuit breaker techniques
[RFC8084], or blocking of uncharacterised traffic), and this needs to [RFC8084], or blocking of uncharacterised traffic), and this needs to
be considered when evaluating the impact of designs for transport be considered when evaluating the impact of designs for transport
encryption [RFC5218]. encryption [RFC5218].
skipping to change at page 29, line 12 skipping to change at page 30, line 51
deployed transports and their applications. Encryption of the deployed transports and their applications. Encryption of the
transport information prevents tools from directly observing this transport information prevents tools from directly observing this
information. A variety of open source and commercial tools have been information. A variety of open source and commercial tools have been
deployed that utilise this information for a variety of short and deployed that utilise this information for a variety of short and
long term measurements. long term measurements.
The network will not break just because transport headers are The network will not break just because transport headers are
encrypted, although alternative diagnostic and troubleshooting tools encrypted, although alternative diagnostic and troubleshooting tools
would need to be developed and deployed. Introducing a new protocol would need to be developed and deployed. Introducing a new protocol
or application can require these tool chains and practice to be or application can require these tool chains and practice to be
updated, and may in turn impact operational mechanisms, and policies. updated, and could in turn impact operational mechanisms, and
Each change can introduce associated costs, including the cost of policies. Each change can introduce associated costs, including the
collecting data, and the tooling needed to handle multiple formats cost of collecting data, and the tooling needed to handle multiple
(possibly as these co-exist in the network, when measurements need to formats (possibly as these co-exist in the network, when measurements
span time periods during which changes are deployed, or to compare need to span time periods during which changes are deployed, or to
with historical data). These costs are incurred by an operator to compare with historical data). These costs are incurred by an
manage the service and debug network issues. operator to manage the service and debug network issues.
At the time of writing, the additional operational cost of using At the time of writing, the additional operational cost of using
encrypted transports is not yet well understood. Design trade-offs encrypted transports is not yet well understood. Design trade-offs
could mitigate these costs by explicitly choosing to expose selected could mitigate these costs by explicitly choosing to expose selected
information (e.g., header invariants and the spin-bit in QUIC information (e.g., header invariants and the spin-bit in QUIC
[I-D.ietf-quic-transport]), the specification of common log formats, [I-D.ietf-quic-transport]), the specification of common log formats,
and development of alternative approaches. and development of alternative approaches.
6.5. Impact on Research, Development and Deployment 6.5. Impact on Research, Development and Deployment
skipping to change at page 30, line 44 skipping to change at page 32, line 33
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 information.
7. Conclusions 7. Conclusions
Confidentiality and strong integrity checks have properties that are Header encryption and strong integrity checks are being incorporated
being incorporated into new protocols and that have important into new transport protocols and have important benefits. The pace
benefits. The pace of development of transports using the WebRTC of development of transports using the WebRTC data channel, and the
data channel, and the rapid deployment of the QUIC transport rapid deployment of the QUIC transport protocol, can both be
protocol, can both be attributed to using the combination of UDP as a attributed to using the combination of UDP as a substrate while
substrate while providing confidentiality and authentication of the providing confidentiality and authentication of the encapsulated
encapsulated transport headers and payload. transport headers and payload.
To achieve stable Internet operations, the IETF transport community To achieve stable Internet operations, the IETF transport community
has, to date, relied heavily on measurement and insights of the has, to date, relied heavily on measurement and insights of the
network operations community to understand the trade-offs, and to network operations community to understand the trade-offs, and to
inform selection of appropriate mechanisms, to ensure a safe, inform selection of appropriate mechanisms, to ensure a safe,
reliable, and robust Internet (e.g., [RFC1273],[RFC2914]). reliable, and robust Internet (e.g., [RFC1273],[RFC2914]).
The traffic that can be observed by on-path network devices is a The traffic that can be observed by on-path network devices (the
function of transport protocol design/options, network use, "wire image") is a function of transport protocol design/options,
applications, and user characteristics. In general, when only a network use, applications, and user characteristics. In general,
small proportion of the traffic has a specific (different) when only a small proportion of the traffic has a specific
characteristic, such traffic seldom leads to operational concern, (different) characteristic, such traffic seldom leads to operational
although the ability to measure and monitor it is less. The desire concern, although the ability to measure and monitor it is less. The
to understand the traffic and protocol interactions typically grows desire to understand the traffic and protocol interactions typically
as the proportion of traffic increases in volume. The challenges grows as the proportion of traffic increases in volume. The
increase when multiple instances of an evolving protocol contribute challenges increase when multiple instances of an evolving protocol
to the traffic that share network capacity. contribute to the traffic that share network capacity.
An increased pace of evolution therefore needs to be accompanied by An increased pace of evolution therefore needs to be accompanied by
methods that can be successfully deployed and used across operational methods that can be successfully deployed and used across operational
networks. This leads to a need for network operators at various networks. This leads to a need for network operators at various
levels (ISPs, enterprises, firewall maintainer, etc.) to identify levels (ISPs, enterprises, firewall maintainer, etc.) to identify
appropriate operational support functions and procedures. appropriate operational support functions and procedures. Protocols
that change their transport header format (wire image) or their
Protocols that change their transport header format (wire format) or behaviour (e.g., algorithms that are needed to classify and
their behaviour (e.g., algorithms that are needed to classify and characterise the protocol), will require new network tooling to be
characterise the protocol), will require new tooling to be developed developed to catch-up with each change. If a protocol changes so
to catch-up with the change. If the currently deployed tools and that the currently deployed tools and methods are no longer relevant,
methods are no longer relevant, then it may no longer be possible to then these tools can not be used to measure performance. This can
correctly measure performance. This can increase the response-time increase the response-time after faults, and can impact the ability
after faults, and can impact the ability to manage the network to manage the network resulting in traffic causing traffic to be
resulting in traffic causing traffic to be treated inappropriately treated inappropriately (e.g., rate-limiting as a result of incorrect
(e.g., rate limiting because of being incorrectly classified/ classification or monitoring).
monitored).
There are benefits in exposing consistent information to the network There are benefits in exposing consistent information to the network
that avoids traffic being inappropriately classified and then that avoids traffic being inappropriately classified and then
receiving a default treatment by the network. The flow label and receiving a default treatment by the network. The flow label and
DSCP fields provide examples of how transport information can be made DSCP fields provide examples of how transport information can be made
available for network-layer decisions. Extension headers could also available for network-layer decisions. Extension headers could also
be used to carry transport information that can inform network-layer be used to carry transport information that can inform network-layer
decisions. Other information may also be useful to various decisions. Other information might also be useful to various
stakeholders, however this document does not make recommendations stakeholders, however this document does not make recommendations
about what information should be exposed, to whom it should be about what information ought to be exposed, to whom it ought to be
observable, or how this will be achieved. observable, or how this will be achieved.
There are trade-offs and implications of increased use of encryption There are trade-offs and implications of increased use of transport
when designing a protocol. Transport protocol designers have often header encryption when designing a protocol. Transport protocol
ignored the implications of whether the information in transport designers have often ignored the implications of whether the
header fields can or will be used by in-network devices, and the information in transport header fields can or will be used by in-
implications this places on protocol evolution. This motivates a network devices, and the implications this places on protocol
design that provides confidentiality of header information. This evolution. This motivates a design that provides confidentiality of
lack of visibility of transport header information can be expected to header information. This lack of visibility of transport header
impact the ways that protocols are deployed, standardised, and their information can be expected to impact the ways that protocols are
operational support. The impact of hiding transport headers deployed, standardised, and their operational support. The impact of
therefore needs to be considered in the specification and development hiding transport headers therefore needs to be considered in the
of protocols and standards. This has a potential impact on the way specification and development of protocols and standards. This has a
in which the IRTF and IETF develop new protocols, specifications, and potential impact on the way in which the IRTF and IETF develop new
guidelines: protocols, specifications, and guidelines:
o Coexistence of Transport and Network Device Protocols/ o Coexistence of Transport Protocols and Configurations: TCP is
Configuration: Transmission Control Protocol (TCP) is currently currently the predominant transport protocol used over Internet
the predominant transport protocol used over Internet paths. Its paths. Its many variants have broadly consistent approaches to
many variants have broadly consistent approaches to avoiding avoiding congestion collapse, and to ensuring the stability of the
congestion collapse, and to ensuring the stability of the
Internet. Increased use of transport layer encryption can Internet. Increased use of transport layer encryption can
overcome ossification, allowing deployment of new transports and overcome ossification, allowing deployment of new transports and
different types of congestion control. This flexibility can be different types of congestion control. This flexibility can be
beneficial, but it could come at the cost of fragmenting the beneficial, but it could come at the cost of fragmenting the
ecosystem. There is little doubt that developers will try to ecosystem. There is little doubt that developers will try to
produce high quality transports for their intended target uses, produce high quality transports for their intended target uses,
but it is not yet clear there are sufficient incentives to ensure but it is not yet clear there are sufficient incentives to ensure
good practice that benefits the wide diversity of requirements for good practice that benefits the wide diversity of requirements for
the Internet community as a whole. the Internet community as a whole.
o Supporting Common Specifications: Common open specifications can o Supporting Common Specifications: Common open specifications can
stimulate engagement by developers, users, and researchers. stimulate engagement by developers, users, and researchers.
Increased diversity, and the ability to innovate without public Increased diversity, and the ability to innovate without public
scrutiny, risks point solutions that optimise for specific needs, scrutiny, risks point solutions that optimise for specific needs,
but accidentally disrupt operations of/in different parts of the but accidentally disrupt operations of/in different parts of the
network. The social contract that maintains the stability of the network. The social contract that maintains the stability of the
Internet relies on accepting common interworking specifications. Internet relies on accepting common interworking specifications,
and on it being possible to detect violations.
o Benchmarking and Understanding Feature Interactions: An o 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 understand complex feature configurations. This can also help with understanding complex
interactions. An inability to observe transport protocol feature interactions. An inability to observe transport layer
information can limit the ability to diagnose and explore header 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 need to be this information is observed. New approaches will need to be
developed. developed.
o Operational Practice: The network operations community relies on o Operational Practice: The network operations community relies on
being able to understand the pattern and requirements of traffic being able to understand the pattern and requirements of traffic
passing over the Internet, both in aggregate and at the flow passing over the Internet, both in aggregate and at the flow
level. These operational practices have developed based on the level. These operational practices have developed based on the
information available from unencrypted transport headers. The information available from unencrypted transport headers. The
IETF supports this activity by developing operations and IETF supports this activity by developing operations and
management specifications, interface specifications, and management specifications, interface specifications, and
associated Best Current Practice (BCP) specifications. Concealing associated Best Current Practice (BCP) specifications. Concealing
transport header information impacts current practice and demand transport header information impacts current practice and demand
new specifications. new specifications.
o Research and Development: Concealing transport information can o Research and Development: Concealing transport information can
impede independent research into new mechanisms, measurement of impede independent research into new mechanisms, measurement of
behaviour, and development initiatives. Experience shows that behaviour, and development initiatives. Experience shows that
transport protocols are complicated to design and complex to transport protocols are complicated to design and complex to
deploy, and that individual mechanisms need to be evaluated while deploy, and that individual mechanisms need to be evaluated while
considering other mechanisms, across a broad range of network considering other mechanisms, across a broad range of network
topologies and with attention to the impact on traffic sharing the topologies and with attention to the impact on traffic sharing the
capacity. If this results in reduced availability of open data, capacity. If increased use of transport header encryption results
it could eliminate the independent self-checks to the in reduced availability of open data, it could eliminate the
standardisation process that have previously been in place from independent self-checks to the standardisation process that have
research and academic contributors (e.g., the role of the IRTF previously been in place from research and academic contributors
Internet Congestion Control Research Groups (ICCRG) and research (e.g., the role of the IRTF Internet Congestion Control Research
publications in reviewing new transport mechanisms and assessing Group (ICCRG) and research publications in reviewing new transport
the impact of their experimental deployment). mechanisms and assessing the impact of their experimental
deployment).
The choice of whether future transport protocols encrypt their The design of future transport protocols needs to consider encryption
protocol headers needs to be taken based not solely on security and of their transport headers to satisfy security and privacy concerns.
privacy considerations, but also taking into account the impact on This choice to encrypt all, or part, of the transport layer protocol
operations, standards and research. As [RFC7258] notes: "Making headers needs to also take into account the impact on operations,
networks unmanageable to mitigate (pervasive monitoring) is not an standards, and research. As [RFC7258] notes, "Making networks
acceptable outcome, but ignoring (pervasive monitoring) would go unmanageable to mitigate (pervasive monitoring) is not an acceptable
against the consensus documented here." outcome, but ignoring (pervasive monitoring) would go against the
consensus documented here."
As part of a protocol's design, the community therefore needs to As part of a protocol's design, the community therefore needs to
weigh the benefits of ossifying common headers versus the potential weigh the benefits of ossifying common headers versus the potential
demerits of exposing specific information that could be observed demerits of exposing specific information that could be observed
along the network path, to ensure network operators, researchers and along the network path, to ensure network operators, researchers and
other stakeholders have appropriate tools to manage their networks other stakeholders have appropriate tools to manage their networks
and enable stable operation of the Internet as new protocols are and enable stable operation of the Internet as new protocols are
deployed. An appropriate balance will emerge over time as real deployed. An appropriate balance will emerge over time as real
instances of this tension are analysed [RFC7258]. This balance instances of this tension are analysed [RFC7258]. This balance
between information exposed and information concealed ought to be between information exposed and information concealed ought to be
skipping to change at page 34, line 13 skipping to change at page 36, line 4
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.
Integrity checks can protect an endpoint from undetected modification Integrity checks can protect an endpoint from undetected modification
of protocol fields by network devices, whereas encryption and of protocol fields by network devices, whereas encryption and
obfuscation or greasing can further prevent these headers being obfuscation or greasing can further prevent these headers being
utilised by network devices. Hiding headers can therefore provide utilised by network devices. Hiding headers can therefore provide
the opportunity for greater freedom to update the protocols and can the opportunity for greater freedom to update the protocols and can
ease experimentation with new techniques and their final deployment ease experimentation with new techniques and their final deployment
in endpoints. A protocol specification needs to weigh the benefits in endpoints. A protocol specification needs to weigh the costs of
of ossifying common headers, versus the potential demerits of ossifying common headers, versus the potential benefits of exposing
exposing specific information that could be observed along the specific information that could be observed along the network path to
network path to provide tools to manage new variants of protocols. provide tools to manage new variants of protocols.
A protocol design that uses header encryption can provide A protocol design that uses header encryption can provide
confidentiality of some or all of the protocol header information. confidentiality of some or all of the protocol header information.
This prevents an on-path device from knowledge of the header field. This prevents an on-path device from knowledge of the header field.
It therefore prevents mechanisms being built that directly rely on It therefore prevents mechanisms being built that directly rely on
the information or seeks to infer semantics of an exposed header the information or seeks to infer semantics of an exposed header
field. Hiding headers can limit the ability to measure and field. Hiding headers reduces visibility into transport metadata,
characterise traffic. and can limit the ability to measure and characterise traffic. It
can also provide privacy benefits in some cases.
Exposed transport headers are sometimes utilised as a part of the Exposed transport headers are sometimes utilised as a part of the
information to detect anomalies in network traffic. This can be used information to detect anomalies in network traffic. This can be used
as the first line of defence to identify potential threats from DOS as the first line of defence to identify potential threats from DOS
or malware and redirect suspect traffic to dedicated nodes or malware and redirect suspect traffic to dedicated nodes
responsible for DOS analysis, malware detection, or to perform packet responsible for DOS analysis, malware detection, or to perform packet
"scrubbing" (the normalization of packets so that there are no "scrubbing" (the normalization of packets so that there are no
ambiguities in interpretation by the ultimate destination of the ambiguities in interpretation by the ultimate destination of the
packet). These techniques are currently used by some operators to packet). These techniques are currently used by some operators to
also defend from distributed DOS attacks. also defend from distributed DOS attacks.
Exposed transport header fields are sometimes also utilised as a part Exposed transport header fields are sometimes also utilised as a part
of the information used by the receiver of a transport protocol to of the information used by the receiver of a transport protocol to
protect the transport layer from data injection by an attacker. In protect the transport layer from data injection by an attacker. In
evaluating this use of exposed header information, it is important to evaluating this use of exposed header information, it is important to
consider whether it introduces a significant DOS threat. For consider whether it introduces a significant DOS threat. For
example, an attacker could construct a DOS attack by sending packets example, an attacker could construct a DOS attack by sending packets
with a sequence number that falls within the currently accepted range with a sequence number that falls within the currently accepted range
of sequence numbers at the receiving endpoint, this would then of sequence numbers at the receiving endpoint, this would then
introduce additional work at the receiving endpoint, even though the introduce additional work at the receiving endpoint, even though the
data in the attacking packet may not finally be delivered by the data in the attacking packet might not finally be delivered by the
transport layer. This is sometimes known as a "shadowing attack". transport layer. This is sometimes known as a "shadowing attack".
An attack can, for example, disrupt receiver processing, trigger loss An attack can, for example, disrupt receiver processing, trigger loss
and retransmission, or make a receiving endpoint perform unproductive and retransmission, or make a receiving endpoint perform unproductive
decryption of packets that cannot be successfully decrypted (forcing decryption of packets that cannot be successfully decrypted (forcing
a receiver to commit decryption resources, or to update and then a receiver to commit decryption resources, or to update and then
restore protocol state). restore protocol state).
One mitigation to off-path attack is to deny knowledge of what header One mitigation to off-path attack is to deny knowledge of what header
information is accepted by a receiver or obfuscate the accepted information is accepted by a receiver or obfuscate the accepted
header information, e.g., setting a non-predictable initial value for header information, e.g., setting a non-predictable initial value for
a sequence number during a protocol handshake, as in [RFC3550] and a sequence number during a protocol handshake, as in [RFC3550] and
skipping to change at page 36, line 9 skipping to change at page 37, line 51
The authors would like to thank Mohamed Boucadair, Spencer Dawkins, The authors would like to thank Mohamed Boucadair, Spencer Dawkins,
Tom Herbert, Jana Iyengar, Mirja Kuehlewind, Kyle Rose, Kathleen Tom Herbert, Jana Iyengar, Mirja Kuehlewind, Kyle Rose, Kathleen
Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, Chris Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, Chris
Wood, Thomas Fossati, and other members of the TSVWG for their Wood, Thomas Fossati, and other members of the TSVWG for their
comments and feedback. comments and feedback.
This work has received funding from the European Union's Horizon 2020 This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No 688421, research and innovation programme under grant agreement No 688421,
and the EU Stand ICT Call 4. The opinions expressed and arguments and the EU Stand ICT Call 4. The opinions expressed and arguments
employed reflect only the authors' view. The European Commission is employed reflect only the authors' view. The European Commission is
not responsible for any use that may be made of that information. not responsible for any use that might be made of that information.
This work has received funding from the UK Engineering and Physical This work has received funding from the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1. Sciences Research Council under grant EP/R04144X/1.
11. Informative References 11. Informative References
[bufferbloat] [bufferbloat]
Gettys, J. and K. Nichols, "Bufferbloat: dark buffers in Gettys, J. and K. Nichols, "Bufferbloat: dark buffers in
the Internet. Communications of the ACM, 55(1):57-65", the Internet. Communications of the ACM, 55(1):57-65",
January 2012. January 2012.
[I-D.ietf-ippm-ioam-data] [I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., Pignataro, C., Gredler, H., Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon, P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
"Data Fields for In-situ OAM", draft-ietf-ippm-ioam- "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
data-06 (work in progress), July 2019. data-06 (work in progress), July 2019.
[I-D.ietf-quic-spin-exp]
Trammell, B. and M. Kuehlewind, "The QUIC Latency Spin
Bit", draft-ietf-quic-spin-exp-01 (work in progress),
October 2018.
[I-D.ietf-quic-transport] [I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-22 (work and Secure Transport", draft-ietf-quic-transport-22 (work
in progress), July 2019. in progress), July 2019.
[I-D.ietf-rtcweb-overview] [I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-19 Browser-based Applications", draft-ietf-rtcweb-overview-19
(work in progress), November 2017. (work in progress), November 2017.
skipping to change at page 43, line 5 skipping to change at page 44, line 29
[RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a [RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
2019, <https://www.rfc-editor.org/info/rfc8546>. 2019, <https://www.rfc-editor.org/info/rfc8546>.
[RFC8548] Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack, [RFC8548] Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic Protection of TCP Streams Q., and E. Smith, "Cryptographic Protection of TCP Streams
(tcpcrypt)", RFC 8548, DOI 10.17487/RFC8548, May 2019, (tcpcrypt)", RFC 8548, DOI 10.17487/RFC8548, May 2019,
<https://www.rfc-editor.org/info/rfc8548>. <https://www.rfc-editor.org/info/rfc8548>.
[RFC8558] Hardie, T., Ed., "Transport Protocol Path Signals",
RFC 8558, DOI 10.17487/RFC8558, April 2019,
<https://www.rfc-editor.org/info/rfc8558>.
Appendix A. Revision information Appendix A. Revision information
-00 This is an individual draft for the IETF community. -00 This is an individual draft for the IETF community.
-01 This draft was a result of walking away from the text for a few -01 This draft was a result of walking away from the text for a few
days and then reorganising the content. days and then reorganising the content.
-02 This draft fixes textual errors. -02 This draft fixes textual errors.
-03 This draft follows feedback from people reading this draft. -03 This draft follows feedback from people reading this draft.
skipping to change at page 44, line 40 skipping to change at page 46, line 40
Section 2 deserved some work to make it easier to read and avoid Section 2 deserved some work to make it easier to read and avoid
repetition. This edit finally gets to this, and eliminates some repetition. This edit finally gets to this, and eliminates some
duplication. This also moves some of the material from section 2 to duplication. This also moves some of the material from section 2 to
reform a clearer conclusion. The scope remains focussed on the usage reform a clearer conclusion. The scope remains focussed on the usage
of transport headers and the implications of encryption - not on of transport headers and the implications of encryption - not on
proposals for new techniques/specifications to be developed. proposals for new techniques/specifications to be developed.
-08 Addressed feedback and completed editorial work, including -08 Addressed feedback and completed editorial work, including
updating the text referring to RFC7872, in preparation for a WGLC. updating the text referring to RFC7872, in preparation for a WGLC.
-09 Updated following WGLC. In particular, thanks to Joe Touch
(specific comments and commentry on style and tone); Dimitri Tikonov
(editorial); Christian Huitema (various) David Black (various).
Ammended privacy considerations based on SECDIR review. Emile
Stephan (inputs on operations measurement); Various others.
Added summary text and refs to key sections. Note to editors: The
section numbers are hard-linked.
Authors' Addresses Authors' Addresses
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Department of Engineering Department of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen AB24 3UE Aberdeen AB24 3UE
Scotland Scotland
EMail: gorry@erg.abdn.ac.uk EMail: gorry@erg.abdn.ac.uk
skipping to change at page 45, line 4 skipping to change at page 47, line 16
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Department of Engineering Department of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen AB24 3UE Aberdeen AB24 3UE
Scotland Scotland
EMail: gorry@erg.abdn.ac.uk EMail: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/ URI: http://www.erg.abdn.ac.uk/
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
School of Computing Science School of Computing Science
Glasgow G12 8QQ Glasgow G12 8QQ
Scotland Scotland
EMail: csp@csperkins.org EMail: csp@csperkins.org
URI: https://csperkins.org// URI: https://csperkins.org/
 End of changes. 116 change blocks. 
619 lines changed or deleted 712 lines changed or added

This html diff was produced by rfcdiff 1.45. The latest version is available from http://tools.ietf.org/tools/rfcdiff/