draft-fairhurst-tsvwg-transport-encrypt-06.txt   draft-fairhurst-tsvwg-transport-encrypt-07.txt 
TSVWG G. Fairhurst TSVWG G. Fairhurst
Internet-Draft University of Aberdeen Internet-Draft University of Aberdeen
Intended status: Informational C.S. Perkins Intended status: Informational C.S. Perkins
Expires: August 11, 2018 University of Glasgow Expires: October 10, 2018 University of Glasgow
February 9, 2018 April 10, 2018
The Impact of Transport Header Confidentiality on Network Operation and The Impact of Transport Header Confidentiality on Network Operation and
Evolution of the Internet Evolution of the Internet
draft-fairhurst-tsvwg-transport-encrypt-06 draft-fairhurst-tsvwg-transport-encrypt-07
Abstract Abstract
This document describes implications of applying end-to-end This document describes implications of applying end-to-end
encryption at the transport layer. It identifies in-network uses of encryption at the transport layer. It identifies in-network uses of
transport layer header information. It then reviews the implications transport layer header information. It then reviews the implications
of developing end-to-end transport protocols that use encryption to of developing end-to-end transport protocols that use encryption to
provide confidentiality of the transport protocol header and expected provide confidentiality of the transport protocol header and expected
implications of transport protocol design and network operation. implications of transport protocol design and network operation.
Since transport measurement and analysis of the impact of network Since transport measurement and analysis of the impact of network
skipping to change at page 1, line 41 skipping to change at page 1, line 41
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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 11, 2018. This Internet-Draft will expire on October 10, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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 (http://trustee.ietf.org/ Provisions Relating to IETF Documents (http://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License. provided without warranty as described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Current uses of Transport Headers within the Network . . . . . 8 2. Current uses of Transport Headers within the Network . . . . . 8
2.1. Observing Transport Information in the Network . . . . . . 8 2.1. Observing Transport Information in the Network . . . . . . 9
2.1.1. Flow Identification . . . . . . . . . . . . . . . . . 9 2.1.1. Flow Identification . . . . . . . . . . . . . . . . . 9
2.1.2. Metrics derived from Transport Layer Headers . . . . . 9 2.1.2. Metrics derived from Transport Layer Headers . . . . . 10
2.1.3. Metrics derived from Network Layer Headers . . . . . . 12 2.1.3. Metrics derived from Network Layer Headers . . . . . . 12
2.2. Transport Measurement . . . . . . . . . . . . . . . . . . 14 2.2. Transport Measurement . . . . . . . . . . . . . . . . . . 14
2.2.1. Point of Measurement . . . . . . . . . . . . . . . . . 14 2.2.1. Point of Measurement . . . . . . . . . . . . . . . . . 14
2.2.2. Use by Operators to Plan and Provision Networks . . . 15 2.2.2. Use by Operators to Plan and Provision Networks . . . 15
2.2.3. Service Performance Measurement . . . . . . . . . . . 15 2.2.3. Service Performance Measurement . . . . . . . . . . . 15
2.2.4. Measuring Transport to Support Network Operations . . 16 2.2.4. Measuring Transport to Support Network Operations . . 16
2.3. Use for Network Diagnostics and Troubleshooting . . . . . 17 2.3. Use for Network Diagnostics and Troubleshooting . . . . . 17
2.3.1. Examples of measurements . . . . . . . . . . . . . . . 17 2.3.1. Examples of measurements . . . . . . . . . . . . . . . 18
2.4. Observing Headers to Implement Network Policy . . . . . . 18 2.4. Observing Headers to Implement Network Policy . . . . . . 19
3. Encryption and Authentication of Transport Headers . . . . . . 18 3. Encryption and Authentication of Transport Headers . . . . . . 19
3.1. Authenticating the Transport Protocol Header . . . . . . . 20 3.1. Authenticating the Transport Protocol Header . . . . . . . 21
3.2. Encrypting the Transport Payload . . . . . . . . . . . . . 20 3.2. Encrypting the Transport Payload . . . . . . . . . . . . . 21
3.3. Encrypting the Transport Header . . . . . . . . . . . . . 20 3.3. Encrypting the Transport Header . . . . . . . . . . . . . 21
3.4. Authenticating Transport Information and Selectively 3.4. Authenticating Transport Information and Selectively
Encrypting the Transport Header . . . . . . . . . . . . . 21 Encrypting the Transport Header . . . . . . . . . . . . . 22
3.5. Optional Encryption of Header Information . . . . . . . . 21 3.5. Optional Encryption of Header Information . . . . . . . . 22
4. Addition of Transport Information to Network-Layer Protocol 4. Addition of Transport Information to Network-Layer Protocol
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5. Implications of Protecting the Transport Headers . . . . . . . 22 5. Implications of Protecting the Transport Headers . . . . . . . 23
5.1. Independent Measurement . . . . . . . . . . . . . . . . . 22 5.1. Independent Measurement . . . . . . . . . . . . . . . . . 23
5.2. Characterising "Unknown" Network Traffic . . . . . . . . . 23 5.2. Characterising "Unknown" Network Traffic . . . . . . . . . 24
5.3. Accountability and Internet Transport Protocols . . . . . 23 5.3. Accountability and Internet Transport Protocols . . . . . 24
5.4. Impact on Research, Development and Deployment . . . . . . 24 5.4. Impact on Research, Development and Deployment . . . . . . 25
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 25 6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 26
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 27 8. Security Considerations . . . . . . . . . . . . . . . . . . . 29
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.1. Normative References . . . . . . . . . . . . . . . . . . 28 10.1. Normative References . . . . . . . . . . . . . . . . . . 29
10.2. Informative References . . . . . . . . . . . . . . . . . 28 10.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Revision information . . . . . . . . . . . . . . . . . 32 Appendix A. Revision information . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction 1. Introduction
This document describes implications of applying end-to-end This document describes implications of applying end-to-end
encryption at the transport layer. It reviews the implications of encryption at the transport layer. It reviews the implications of
developing end-to-end transport protocols that use encryption to developing end-to-end transport protocols that use encryption to
provide confidentiality of the transport protocol header and expected provide confidentiality of the transport protocol header and expected
implications of transport protocol design and network operation. It implications of transport protocol design and network operation. It
also considers anticipated implications on transport and application also considers anticipated implications on transport and application
evolution. evolution.
The transport layer provides the first end-to-end interactions across The transport layer provides the first end-to-end interactions across
the Internet. Transport protocols layer directly over the network- the Internet. Transport protocols layer directly over the network-
layer service and are sent in the payload of network-layer packets. layer service and are sent in the payload of network-layer packets.
They support end-to-end communication between applications, supported They support end-to-end communication between applications, supported
by higher-layer protocols, running on the end systems (or transport by higher-layer protocols, running on the end systems (or transport
endpoints). This simple architectural view hides one of the core endpoints). This simple architectural view hides one of the core
functions of the transport, however - to discover and adapt to the functions of the transport, however, to discover and adapt to the
properties of the Internet path that is currently being used. The properties of the Internet path that is currently being used. The
design of Internet transport protocols is as much about trying to design of Internet transport protocols is as much about trying to
avoid the unwanted side effects of congestion on a flow and other avoid the unwanted side effects of congestion on a flow and other
capacity-sharing flows, avoiding congestion collapse, adapting to capacity-sharing flows, avoiding congestion collapse, adapting to
changes in the path characteristics, etc., as it is about end-to-end changes in the path characteristics, etc., as it is about end-to-end
feature negotiation, flow control and optimising for performance of a feature negotiation, flow control and optimising for performance of a
specific application. specific application.
To achieve stable Internet operations the IETF transport community To achieve stable Internet operations the IETF transport community
has to date relied heavily on measurement and insights of the network has to date relied heavily on measurement and insights of the network
operations community to understand the trade-offs, and to inform operations community to understand the trade-offs, and to inform
selection of appropriate mechanisms, to ensure a safe, reliable, and selection of appropriate mechanisms, to ensure a safe, reliable, and
robust Internet (e.g., [RFC1273]). In turn, the network operations robust Internet (e.g., [RFC1273]). In turn, the network operations
community relies on being able to understand the pattern and community relies on being able to understand the pattern and
requirements of traffic passing over the Internet, both in aggregate requirements of traffic passing over the Internet, both in aggregate
and at the flow level - inspecting transport layer headers to help and at the flow level.
understand traffic dynamics.
There are many motivations for deploying encrypted transports (i.e., There are many motivations for deploying encrypted transports (i.e.,
transport protocols that use encryption to provide confidentiality of transport protocols that use encryption to provide confidentiality of
some or all of the transport-layer header information), and some or all of the transport-layer header information), and
encryption of transport payloads (i.e. Confidentiality of the encryption of transport payloads (i.e. confidentiality of the
payload data). The increasing public concerns about the interference payload data). The increasing public concerns about the interference
with Internet traffic have led to a rapidly expanding deployment of with Internet traffic have led to a rapidly expanding deployment of
encryption to protect end-user privacy, in protocols like QUIC, but encryption to protect end-user privacy, in protocols like QUIC [I-D
also expected to forma a basis of future protocol designs. .ietf-quic-transport], but also expected to form a basis of future
protocol designs.
Introducing cryptographic integrity checks to header fields can also
prevent undetected manipulation of the field by network devices.
However, it does not prevent inspection of the information by device
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. This leads to ossification of the header: An
endpoint could be required to supply the header to receive the
network service that it desires. In some cases, this could be benign
to the protocol (e.g., recognising the start of a connection), but in
other cases, any change to the protocol use of a specific header can
have undesirable implications (e.g., 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 could prevent the device
from forwarding packets using a different version of a protocol that
introduces a new feature that changes the value present in this
field). A protocol that intentionally varies the format and value of
header fields (sometimes known as Greasing) has been suggested as a
way to help avoid such ossification of the transport protocol.
Implementations of network devices are encouraged to avoid side- Implementations of network devices are encouraged to avoid side-
effects when protocols are updated. In particular, it is important effects when protocols are updated. Introducing cryptographic
that protocols either do not expose information where the usage may integrity checks to header fields can also prevent undetected
change in future protocols, or that methods that utilise the manipulation of the field by network devices, or undetected addition
information are robust to potential changes as protocols evolve over of information to a packet. However, this does not prevent
time. inspection of the information by a device on path, and it is possible
that such devices could develop mechanisms that rely on the presence
At the same time, some network operators and access providers, have of such a field, or a known value in the field. Reliance on the
come to rely on the in-network measurement of transport properties presence and semantics of packet headers leads to ossification: An
and the functionality provided by middleboxes to both support network endpoint could be required to supply a specific header to receive the
operations and enhance performance (e.g., [I-D.dolson-plus-middlebox- network service that it desires. In some cases, this could be benign
benefits]). to the protocol (e.g., recognising the start of a connection), but
not in all cases (e.g., a mechanism implemented in a network device,
such as a firewall, could require a header field to have only a
specific known set of values could prevent the device from forwarding
packets using a different version of a protocol that introduces a new
feature that changes the value present in this field).
A protocol design can use header encryption to provide A protocol design can use header encryption to 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 imply semantics of an exposed header the information or seeks to imply semantics of an exposed header
field. Protocol designers have often ignored these implications and field. Using encryption to provide confidentiality of the transport
this document suggests that exposure of information should be layer brings some well-known privacy and security benefits and can
carefully considered when specifying new protocols. therefore help reduce ossification of the transport layer. In
particular, it is important that protocols either do not expose
information where the usage may change in future protocols, or that
methods that utilise the information are robust to potential changes
as protocols evolve over time. To avoid unwanted inspection, a
protocol could also intentionally vary the format and value of header
fields (sometimes known as Greasing [I-D.thomson-quic-grease]).
Using encryption to provide confidentiality of the transport layer At the same time, some network operators and access providers, have
brings some well-known privacy and security benefits. While a come to rely on the in-network measurement of transport properties
protocol design that encrypts (hides) all the transport information and the functionality provided by middleboxes to both support network
can help reduce ossification of the transport layer, it could result operations and enhance performance. There can therefore be
in ossification of the network service. There can be advantages in implications when working with encrypted transport protocols that
providing a level of ossification of the header in terms of providing hide transport header information from the network. This present
a set of specified header fields that are observable from in-network architectural challenges and considerations in the way transport
devices. protocols are designed, and ability to characterise and compare
different transport solutions [Measure].
There can also be implications when working with encrypted transport A level of ossification of the header can be advantageous in terms of
protocols that hide transport header information from the network. providing a set of specified header fields that become observable by
This present architectural challenges and considerations in the way in-network devices. This results in trade-offs around
transport protocols are designed, and ability to characterise and authentication, and confidentiality of transport protocol headers and
compare different transport solutions [Measure]. This results in the potential support for other uses of this header information. For
trade-offs around authentication, and confidentiality of transport example, a design that provides confidentiality of protocol header
protocol headers and the potential support for other uses of this information can impact the following activities that rely on
header information. For example, it can impact the following measurement and analysis of traffic flows:
activities that rely on measurement and analysis of traffic flows:
Network Operations and Research: Observable transport headers enable Network Operations and Research: Observable transport headers enable
both operators and the research community to measure and analyse both operators and the research community to measure and analyse
protocol performance, network anomalies, and failure pathologies. protocol performance, network anomalies, and failure pathologies.
This information can help inform capacity planning, and assist in This information can help inform capacity planning, and assist in
determining the need for equipment and/or configuration changes by determining the need for equipment and/or configuration changes by
network operators. network operators.
This data information can inform Internet engineering research, The data can also inform Internet engineering research, and help
and help the development of new protocols, methodologies, and the development of new protocols, methodologies, and procedures.
procedures. Hiding the entire transport protocol, including Concealing the transport protocol header information makes the
header information, will restrict the availability of data, and stream performance unavailable to passive observers along the
might lead to the development of alternative, and potentially more path, and likely leads to the development of alternative methods
intrusive, methods to acquire the needed data. to collect or infer that data.
Providing confidentiality of the transport payload, but leaving Providing confidentiality of the transport payload, but leaving
some, or all, of the transport headers unencrypted, possibly with some, or all, of the transport headers unencrypted, possibly with
authentication, can provide the majority of the privacy and authentication, can provide the majority of the privacy and
security benefits while allowing some measurement. security benefits while allowing some measurement.
Protection from Denial of Service: Observable transport headers can Protection from Denial of Service: Observable transport headers
provide useful input to classification of traffic and detection of currently provide useful input to classify traffic and detect
anomalous events, such as distributed denial of service attacks. anomalous events (e.g., changes in application behaviour,
To be effective, this protection needs to be able to uniquely distributed denial of service attacks). To be effective, this
disambiguate unwanted traffic. An inability to separate this protection needs to be able to uniquely disambiguate unwanted
traffic using packet header information is expected to lead to traffic. An inability to separate this traffic using packet
less precise pattern matching techniques or resort to header information may result in less-efficient identification of
indiscriminately (rate) limiting uncharacterised traffic. unwanted traffic or development of different methods (e.g. rate-
limiting of uncharacterised traffic).
Network Troubleshooting and Diagnostics: Encrypting transport header Network Troubleshooting and Diagnostics: Encrypting transport header
information eliminates the incentive for operators to troubleshoot information eliminates the incentive for operators to troubleshoot
what they cannot interpret. A flow experiencing packet loss looks what they cannot interpret. A flow experiencing packet loss or
like an unaffected flow when only observing network layer headers jitter looks like an unaffected flow when only observing network
(if transport sequence numbers and flow identifiers are obscured). layer headers (if transport sequence numbers and flow identifiers
This limits understanding of the impact of packet loss on the are obscured). This limits understanding of the impact of packet
flows that share a network segment. Encrypted traffic therefore loss or latency on the flows, or even localizing the network
implies "don't touch", and a likely trouble-shooting response will segment causing the packet loss or latency. Encrypted traffic may
be "can't help, no trouble found". The additional mechanisms that imply "don't touch" to some, and could limit a trouble-shooting
will need to be introduced to help reconstruct transport-level response to "can't help, no trouble found". The additional
metrics add complexity and operational costs [I-D.mm-wg-effect- mechanisms that will need to be introduced to help reconstruct
encrypt]. transport-level metrics add complexity and operational costs
(e.g., in deploying additional functions in equipment or adding
traffic overhead).
Network Traffic Analysis: Hiding transport protocol header Network Traffic Analysis: Hiding transport protocol header
information can make it harder to determine which transport information can make it harder to determine which transport
protocols and features are being used across a network segment. protocols and features are being used across a network segment and
The trends in usage. This could impact the ability for an to measure trends in the pattern of usage. This could impact the
operator to anticipate the need for network upgrades and roll-out. ability for an operator to anticipate the need for network
It can also impact the on-going traffic engineering activities upgrades and roll-out. It can also impact the on-going traffic
performed by operators. While the impact may, in many cases, be engineering activities performed by operators (such as determining
small there are scenarios where operators directly support which parts of the path contribute delay, jitter or loss). While
particular services (e.g., in radio links, or to troubleshoot the impact may, in many cases, be small there are scenarios where
issues relating to Quality of Service, QoS; the ability to perform operators directly support particular services (e.g., to
fast re-routing of critical traffic, or support to mitigate the troubleshoot issues relating to Quality of Service, QoS; the
characteristics of specific radio links). The more complex the ability to perform fast re-routing of critical traffic, or support
underlying infrastructure the more important this impact. to mitigate the characteristics of specific radio links). The more
complex the underlying infrastructure the more important this
impact.
Open and Verifiable Network Data: The Hiding transport protocol Open and Verifiable Network Data: Hiding transport protocol header
header information can reduces the range of actors that can information can reduce the range of actors that can capture useful
capture useful measurement data. This is, of course, its goal. measurement data. For example, one approach could be to employ an
Doing so, however, limits the information sources available to the existing transport protocol that reveals little information (e.g.,
Internet community to understand the operation of transport UDP), and perform traditional transport functions at higher layers
protocols, so preventing access to the information necessary to protecting the confidentiality of transport information. Such a
inform design decisions and standards for new protocols and design, limits the information sources available to the Internet
related operational practices. community to understand the operation of new transport protocols,
so preventing access to the information necessary to inform design
decisions and standardisation of the new protocols and related
operational practices.
There are dangers in a model where only endpoints (i.e., at user The cooperating dependence of network, application, and host to
devices and within service platforms) can observe performance, and provide communication performance on the Internet is uncertain
this cannot be independently verified. when only endpoints (i.e., at user devices and within service
platforms) can observe performance, and performance cannot be
independently verified by all parties. The ability of other
stakeholders to review code can help develop deeper insight. In
the heterogeneous Internet, this helps extend the range of
topologies, vendor equipment, and traffic patterns that are
evaluated.
To ensure the health of the standards and research communities, we Independently captured data is important to help ensure the health
need independently captured data to develop new transport protocol of the research and development communities. It can provide input
mechanisms based on the behaviour experienced in deployed and test scenarios to support development of new transport
networks. protocol mechanisms, especially when this analysis can be based on
the behaviour experienced in a diversity of deployed networks.
Independently verifiable performance metrics might also important Independently verifiable performance metrics might also be
in order to demonstrate regulatory compliance in some important to demonstrate regulatory compliance in some
jurisdictions. jurisdictions, and provides an important basis for informing
design decisions.
The last point leads us to consider the impact of hiding transport The last point leads us to consider the impact of hiding transport
headers in the specification and development of protocols and headers in the specification and development of protocols and
standards. This has potential impact on: standards. This has potential impact on:
o Understanding Feature Interactions: An appropriate vantage point, o Understanding Feature Interactions: An appropriate vantage point,
coupled with timing information about traffic flows, provides a coupled with timing information about traffic flows, provides a
valuable tool for benchmarking equipment, functions, and/or valuable tool for benchmarking equipment, functions, and/or
configurations, and to understand complex feature interactions. configurations, and to understand complex feature interactions.
An inability to observe transport protocol information can limit An inability to observe transport protocol information can limit
the ability to diagnose and explore interactions between features the ability to diagnose and explore interactions between features
at different protocol layers, a side-effect of not allowing a at different protocol layers, a side-effect of not allowing a
choice of vantage point from which this information is observed. choice of vantage point from which this information is observed.
o Supporting Common Specifications: The Transmission Control o Supporting Common Specifications: The Transmission Control
Protocol (TCP) is the predominant transport protocol used over Protocol (TCP) is currently the predominant transport protocol
Internet paths. Its many variants have broadly consistent used over Internet paths. Its many variants have broadly
approaches to avoiding congestion collapse, and to ensuring the consistent approaches to avoiding congestion collapse, and to
stability of the network. Increased use of transport layer ensuring the stability of the Internet. Increased use of
encryption can overcome ossification, allowing deployment of new transport layer encryption can overcome ossification, allowing
transports and different types of congestion control. This deployment of new transports and different types of congestion
flexibility can be beneficial, but it can come at the cost of control. This flexibility can be beneficial, but it can come at
fragmenting the ecosystem. There is little doubt that developers the cost of fragmenting the ecosystem. There is little doubt that
will try to produce high quality transports for their target uses, developers will try to produce high quality transports for their
but it is not clear there are sufficient incentives to ensure good intended target uses, but it is not clear there are sufficient
practice that benefits the wide diversity of requirements for the incentives to ensure good practice that benefits the wide
Internet community as a whole. Increased diversity, and the diversity of requirements for the Internet community as a whole.
ability to innovate without public scrutiny, risks point solutions Increased diversity, and the ability to innovate without public
that optimise for specific needs, but accidentally disrupt scrutiny, risks point solutions that optimise for specific needs,
operations of/in different parts of the network. The social but accidentally disrupt operations of/in different parts of the
contract that maintains the stability of the network relies on network. The social contract that maintains the stability of the
accepting common specifications, and on the ability to verify that Internet relies on accepting common specifications, and on the
others also conform. ability to verify that others also conform.
o Operational practice: Published transport specifications allow o Operational practice: Published transport specifications allow
operators to check compliance. This can bring assurance to those operators to check compliance. This can bring assurance to those
operating networks, often avoiding the need to deploy complex operating networks, often avoiding the need to deploy complex
techniques that routinely monitor and manage TCP/IP traffic flows techniques that routinely monitor and manage TCP/IP traffic flows
(e.g. Avoiding the capital and operational costs of deploying (e.g. Avoiding the capital and operational costs of deploying
flow rate-limiting and network circuit-breaker methods [RFC8084]). flow rate-limiting and network circuit-breaker methods [RFC8084]).
When it is not possible to observe transport header information, When it is not possible to observe transport header information,
methods are still needed to confirm that the traffic produced methods are still needed to confirm that the traffic produced
conforms to the expectations of the operator or developer. conforms to the expectations of the operator or developer.
o Restricting research and development: Hiding transport information o Restricting research and development: Hiding transport information
can impede independent research into new mechanisms, measurement can impede independent research into new mechanisms, measurement
of behaviour, and development initiatives. Experience shows that of 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. Hiding transport header information (e.g., by pervasive capacity. If this results in reduced availability of open data,
encryption of transport information) could eliminate the it could eliminate the independent self-checks to the
independent self-checks that have previously been in place from standardisation process that have previously been in place from
research and academic contributors (e.g., the role of the IRTF research and academic contributors (e.g., the role of the IRTF
ICCRG, and research publications in reviewing new transport ICCRG, and research publications in reviewing new transport
mechanisms and assessing the impact of their experimental mechanisms and assessing the impact of their experimental
deployment). deployment)
In summary, a lack of visibility of transport header information can In summary, there are tradeoffs. On the one hand, protocol designers
impact the ways that protocols are designed, standardised, deployed, have often ignored the implications of whether the information in
and operated. The choice of whether future transport protocols transport header fields can or will be used by in-network devices,
encrypt their protocol headers therefore needs to be taken based not and the implications this places on protocol evolution. This
solely on security and privacy considerations, but also taking into motivates a design that provides confidentiality of the header
account the impact on operations, standards, and research. A network information. On the other hand, it can be expected that a lack of
that is secure but unusable due to persistent congestion collapse is visibility of transport header information can impact the ways that
not an improvement, and while that would be an extreme outcome protocols are deployed, standardised, and their operational support.
proposals that impose high costs for very limited benefits need to be The choice of whether future transport protocols encrypt their
considered carefully, to ensure the benefits outweigh the costs. protocol headers therefore needs to be taken based not solely on
security and privacy considerations, but also taking into account the
impact on operations, standards, and research. Any new Internet
transport need to provide appropriate transport mechanisms and
operational support to assure the resulting traffic can not result in
persistent congestion collapse [RFC2914]. This document suggests
that the balance between information exposed and concealed should be
carefully considered when specifying new protocols.
2. Current uses of Transport Headers within the Network 2. Current uses of Transport Headers within the Network
Despite transport headers having end-to-end meaning, some of these Despite transport headers having end-to-end meaning, some of these
transport headers have come to be used in various ways within the transport headers have come to be used in various ways within the
Internet. In response to pervasive monitoring [RFC7624] revelations Internet. In response to pervasive monitoring [RFC7624] revelations
and the IETF consensus that "Pervasive Monitoring is an Attack" and the IETF consensus that "Pervasive Monitoring is an Attack"
[RFC7258], efforts are underway to increase encryption of Internet [RFC7258], efforts are underway to increase encryption of Internet
traffic,. Applying confidentiality to transport header fields would traffic,. Applying confidentiality to transport header fields would
affect how network protocols are designed and used [I-D.mm-wg-effect- affect how protocol information is used [I-D.mm-wg-effect-encrypt].
encrypt]. To understand these implications, it is first necessary to To understand these implications, it is first necessary to understand
understand how transport layer headers are currently observed and/or how transport layer headers are currently observed and/or modified by
modified by middleboxes within the network. middleboxes within the network.
Transport protocols can be designed to encrypt or authenticate Transport protocols can be designed to encrypt or authenticate
transport header fields. Authentication methods at the transport transport header fields. Authentication at the transport layer can
layer can be used to detect any changes to an immutable header field be used to detect any changes to an immutable header field that were
that were made by a network device along a path. The intentional made by a network device along a path. The intentional modification
modification of transport headers by middleboxes (such as Network of transport headers by middleboxes (such as Network Address
Address Translation, NAT, or Firewalls) is not considered. Common Translation, NAT, or Firewalls) is not considered. Common issues
issues concerning IP address sharing are described in [RFC6269]. concerning IP address sharing are described in [RFC6269].
2.1. Observing Transport Information in the Network 2.1. Observing Transport Information in the Network
In-network observation of transport protocol headers requires In-network observation of transport protocol headers requires
knowledge of the format of the transport header: knowledge of the format of the transport header:
o Flows need to be identified at the level required for monitoring; o Flows need to be identified at the level required for monitoring;
o The protocol and version of the header need to be observable. As o The protocol and version of the header need to be observable. As
protocols evolve over time and there may be a need to introduce protocols evolve over time and there may be a need to introduce
new transport headers. This may require interpretation of new transport headers. This may require interpretation of
protocol version information or connection setup information; protocol version information or connection setup information;
o Location and syntax of any transport headers to be observed. IETF o Location and syntax of any transport headers needs to be known to
transport protocols specify this information. be observed. IETF transport protocols specify this information.
The following subsections describe various ways that observable The following subsections describe various ways that observable
transport information may be utilised. transport information may be utilised.
2.1.1. Flow Identification 2.1.1. Flow Identification
Transport protocol header information (with information in the Transport protocol header information (together with information in
network header), can identify a flow and the connection state of the the network header), can identify a flow and the connection state of
flow, together with the protocol options being used. In some usages, the flow, together with the protocol options being used. In some
a low-numbered (well-known ) port number can identify a protocol usages, a low-numbered (well-known) transport port number can
(although port information alone is not sufficient to guarantee identify a protocol (although port information alone is not
identification of a protocol). Transport protocols, such as TCP and sufficient to guarantee identification of a protocol). Transport
Stream Control Transport Protocol (SCTP) specify a standard base protocols, such as TCP and Stream Control Transport Protocol (SCTP)
header that includes sequence number information and other data, with specify a standard base header that includes sequence number
the possibility to negotiate additional headers at connection setup, information and other data, with the possibility to negotiate
identified by an option number in the transport header. UDP-based additional headers at connection setup, identified by an option
protocols can use, but sometimes do not use, well-known port numbers. number in the transport header. UDP-based protocols can use, but
Some can instead be identified by signalling protocols or through the sometimes do not use, well-known port numbers. Some can instead be
use of magic numbers placed in the first byte(s) of the datagram identified by signalling protocols or through the use of magic
payload. numbers placed in the first byte(s) of the datagram payload.
Flow identification is more complex and less easily achieved when Flow identification is more complex and less easily achieved when
multiplexing is used at or above the transport layer. multiplexing is used at or above the transport layer.
2.1.2. Metrics derived from Transport Layer Headers 2.1.2. Metrics derived from Transport Layer Headers
Some actors have a need to characterise the performance of link/ Some actors manage their portion of the Internet by characterizing
network segments. Passive monitoring uses observed traffic to makes the performance of link/network segments. Passive monitoring uses
inferences from transport headers to derive these measurements. A observed traffic to makes inferences from transport headers to derive
variety of open source and commercial tools have been deployed that these measurements. A variety of open source and commercial tools
utilise this information. The following metrics can be derived from have been deployed that utilise this information. The following
transport header information: metrics can be derived from transport header information:
Traffic Rate and Volume: Header information e.g., (sequence number, Traffic Rate and Volume: Header information e.g., (sequence number,
length) may allow derivation of volume measures per-application, length) may allow derivation of volume measures per-application,
to characterise the traffic that uses a network segment or the to characterise the traffic that uses a network segment or the
pattern of network usage. This may be measured per endpoint or pattern of network usage. This may be measured per endpoint or
for an aggregate of endpoints (e.g., by an operator to assess for an aggregate of endpoints (e.g., by an operator to assess
subscriber usage). It can also be used to trigger measurement- subscriber usage). It can also be used to trigger measurement-
based traffic shaping and to implement QoS support within the based traffic shaping and to implement QoS support within the
network and lower layers. Volume measures can be valuable for network and lower layers. Volume measures can be valuable for
capacity planning (providing detail of trends rather than the capacity planning (providing detail of trends rather than the
volume per subscriber). volume per subscriber).
Loss Rate and Loss Pattern: Flow loss rate may be derived (e.g., from Loss Rate and Loss Pattern: Flow loss rate may be derived (e.g., from
sequence number) and is often used as a metric for performance sequence number) and is often used as a metric for performance
assessment and to characterise transport behaviour. Understanding assessment and to characterise transport behaviour. Understanding
the root cause of loss can help an operator determine whether this the root cause of loss can help an operator determine whether this
requires corrective action. Network operators may also use the requires corrective action. Network operators may also use the
variation in patterns of loss as a key performance metric, variation in patterns of loss as a key performance metric,
utilising this to detect changes in the offered service. utilising this to detect changes in the offered service.
There are various cause of loss, including: corruption on a link There are various causes of loss, including: corruption of link
(e.g., interference on a radio link), buffer overflow (e.g., due frames (e.g., interference on a radio link), buffer overflow
to congestion), policing (traffic management), buffer management (e.g., due to congestion), policing (traffic management), buffer
(e.g., Active Queue Management, AQM), inadequate provision of management (e.g., Active Queue Management, AQM), inadequate
traffic preemption. Understanding flow loss rate requires either provision of traffic preemption. Understanding flow loss rate
maintaining per flow packet counters or by observing sequence requires either maintaining per flow packet counters or by
numbers in transport headers. Loss can be monitored at the observing sequence numbers in transport headers. Loss can be
interface level by devices in the network. It is often important monitored at the interface level by devices in the network. It is
to understand the conditions under which packet loss occurs. This often important to understand the conditions under which packet
usually requires relating loss to the traffic flowing on the loss occurs. This usually requires relating loss to the traffic
network node/segment at the time of loss. flowing on the network node/segment at the time of loss.
Observation of transport feedback information (observing loss Observation of transport feedback information (observing loss
reports, e.g., RTP Control Protocol (RTCP), TCP SACK) can increase reports, e.g., RTP Control Protocol (RTCP), TCP SACK) can increase
understanding of the impact of loss and help identify cases where understanding of the impact of loss and help identify cases where
loss may have been wrongly identified, or the transport did not loss may have been wrongly identified, or the transport did not
require the lost packet. It is sometimes more important to require the lost packet. It is sometimes more important to
understand the pattern of loss, than the loss rate - since losses understand the pattern of loss, than the loss rate, because losses
can often occur as bursts, rather than randomly-timed events. can often occur as bursts, rather than randomly-timed events.
Throughput and Goodput: The throughput observed by a flow can be Throughput and Goodput: The throughput achieved by a flow can be
determined even when a flow is encrypted, providing the individual determined even when a flow is encrypted, providing the individual
flow can be identified. Goodput [RFC7928] is a measure of useful flow can be identified. Goodput [RFC7928] is a measure of useful
data exchanged (the ratio of useful/total volume of traffic sent data exchanged (the ratio of useful/total volume of traffic sent
by a flow), which requires ability to differentiate loss and by a flow). This requires ability to differentiate loss and
retransmission of packets (e.g., by observing packet sequence retransmission of packets (e.g., by observing packet sequence
numbers in the TCP or the Real Time Protocol, RTP, headers numbers in the TCP or the Real Time Protocol, RTP, headers
[RFC3550]). [RFC3550]).
Latency: Latency is a key performance metric that impacts application Latency: Latency is a key performance metric that impacts application
response time and user-perceived response time. It often response time and user-perceived response time. It often
indirectly impacts throughput and flow completion time. Latency indirectly impacts throughput and flow completion time. Latency
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.
Once the cause of unwanted latency has been identified, this can Once the cause of unwanted latency has been identified, this can
often be eliminated, and determining latency metrics is a key often be eliminated.
driver in the deployment of AQM [RFC7567], DiffServ [RFC2474], and
Explicit Congestion Notification (ECN) [RFC3168] [RFC8087].
To measure latency across a part of a path, an observation point To measure latency across a part of a path, an observation point
can measure the experienced round trip time (RTT) using packet can measure the experienced round trip time (RTT) using packet
sequence numbers, and acknowledgements, or by observing header sequence numbers, and acknowledgements, or by observing header
timestamp information. Such information allows an observation timestamp information. Such information allows an observation
point in the network to determine not only the path RTT, but also point in the network to determine not only the path RTT, but also
to measure the upstream and downstream contribution to the RTT. to measure the upstream and downstream contribution to the RTT.
This may be used to locate a source of latency, e.g., by observing This can be used to locate a source of latency, e.g., by observing
cases where the ratio of median to minimum RTT is large for a part cases where the ratio of median to minimum RTT is large for a part
of a path. of a path.
An example usage of this method could identify excessive buffers The service offered by operators can benefit from latency
to help deploy or configure AQM [RFC7567] [RFC7928] to effectively
eliminate unnecessary queuing in routers and other devices. AQM
methods need to be deployed at the capacity bottleneck, but are
often deployed in combination with other techniques, such as
scheduling [RFC7567] [I-D.ietf-aqm-fq-codel] and although
parameter-less methods are desired [RFC7567], current methods [I-D
.ietf-aqm-fq-codel] [I-D.ietf-aqm-codel] [I-D.ietf-aqm-pie] often
cannot scale across all possible deployment scenarios. The
service offered by operators can therefore benefit from latency
information to understand the impact of deployment and tune information to understand the impact of deployment and tune
deployed services. deployed services. Latency metrics are key to evaluating and
deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit
Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements
could identify excessively large buffers, indicating where to
deploy or configure AQM. An AQM method is often deployed in
combination with other techniques, such as scheduling [RFC7567]
[I-D.ietf-aqm-fq-codel] and although parameter-less methods are
desired [RFC7567], current methods [I-D.ietf-aqm-fq-codel] [I-D
.ietf-aqm-codel] [I-D.ietf-aqm-pie] often cannot scale across all
possible deployment scenarios.
Jitter: Some network applications are sensitive to changes in packet Variation in delay: Some network applications are sensitive to small
timing. For such applications, it can be necessary to measure the changes in packet timing. To assess the performance of such
jitter observed along a portion of the path. The requirements to applications, it can be necessary to measure the variation in
measure jitter resemble those for the measurement of latency. delay observed along a portion of the path [RFC3393] [RFC5481].
The requirements resemble those for the measurement of latency.
Flow Reordering: Significant flow reordering can impact time-critical Flow Reordering: Significant flow reordering can impact time-critical
applications and can be interpreted as loss by reliable applications and can be interpreted as loss by reliable
transports. Many transport protocol techniques are impacted by transports. Many transport protocol techniques are impacted by
reordering (e.g., triggering TCP retransmission, or re-buffering reordering (e.g., triggering TCP retransmission, or re-buffering
of real-time applications). Packet reordering can occur for many of real-time applications). Packet reordering can occur for many
reasons (from equipment design to misconfiguration of forwarding reasons (from equipment design to misconfiguration of forwarding
rules). Since this impacts transport performance, network tools rules). Since this impacts transport performance, network tools
are needed to detect and measure unwanted/excessive reordering. are needed to detect and measure unwanted/excessive reordering.
As in the drive to reduce network latency, there is a need for
operational tools to detect mis-ordered packet flows and quantify
the degree or reordering. Techniques for measuring reordering
typically observe packet sequence numbers. Metrics have been
defined that evaluate whether a network has maintained packet
order on a packet-by-packet basis [RFC4737] and [RFC5236].
There have been initiatives in the IETF transport area to reduce There have been initiatives in the IETF transport area to reduce
the impact of reordering within a transport flow, possibly leading the impact of reordering within a transport flow, possibly leading
to reduce the requirements for ordering. These have promise to to a reduction in the requirements for preserving ordering. These
simplify network equipment design as well as the potential to have promise to simplify network equipment design as well as the
improve robustness of the transport service. Measurements of potential to improve robustness of the transport service.
reordering can help understand the level of reordering within Measurements of reordering can help understand the present level
deployed infrastructure, and inform decisions about how to of reordering within deployed infrastructure, and inform decisions
progress such mechanisms. about how to progress such mechanisms.
Some protocols provide in-built monitoring and reporting functions. Operational tools to detect mis-ordered packet flows and quantify the
Transport fields in the RTP header [RFC3550] [RFC4585] can be degree or reordering. Key performance indicators are retransmission
observed to derive traffic volume measurements and provide rate, packet drop rate, sector utilisation level, a measure of
information on the progress and quality of a session using RTP. Key reordering, peak rate, the CE-marking rate, etc.
performance indicators are retransmission rate, packet drop rate,
sector utilisation level, a measure of reordering, peak rate, the CE- Metrics have been defined that evaluate whether a network has
marking rate, etc. Metadata is often important to understand the maintained packet order on a packet-by-packet basis [RFC4737] and
[RFC5236].
Techniques for measuring reordering typically observe packet sequence
numbers. Some protocols provide in-built monitoring and reporting
functions. Transport fields in the RTP header [RFC3550] [RFC4585]
can be observed to derive traffic volume measurements and provide
information on the progress and quality of a session using RTP. As
with other measurement, metadata is often important to understand the
context under which the data was collected, including the time, context under which the data was collected, including the time,
observation point, and way in which metrics were accumulated. The observation point, and way in which metrics were accumulated. The
RTCP protocol directly reports some of this information in a form RTCP protocol directly reports some of this information in a form
that can be directly visible in the network. A user of summary that can be directly visible in the network. A user of summary
measurement data needs to trust the source of this data and the measurement data needs to trust the source of this data and the
method used to generate the summary information. method used to generate the summary information.
When information in transport headers is concealed, measurements need
to rely on pattern inferences and other heuristics grows, and
accuracy suffers [I-D.mm-wg-effect-encrypt].
2.1.3. Metrics derived from Network Layer Headers 2.1.3. Metrics derived from Network Layer Headers
Some transport information is made visible in the network-layer Some transport information is made visible in the network-layer
protocol header. These header fields are not encrypted and can be protocol header. These header fields are not encrypted and can be
used to make flow observations. utilised to make flow observations.
Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged expose Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged expose
flow information in the IPv6 Flow Label field of the network-layer flow information in the IPv6 Flow Label field of the network-layer
header (e.g., [RFC8085]). This can be used to inform network-layer header (e.g., [RFC8085]). This can be used to inform network-layer
queuing, forwarding (e.g., for equal cost multi-path (ECMP) queuing, forwarding (e.g., for equal cost multi-path, ECMP,
routing, and Link Aggregation, LAG). This can provide useful routing, and Link Aggregation, LAG). This can provide useful
information to assign packets to flows in the data collected by information to assign packets to flows in the data collected by
measurement campaigns. Although important to characterising a measurement campaigns. Although important to characterising a
path, it does not directly provide any performance data. path, it does not directly provide performance data.
Use Network-Layer Differentiated Services Code Point Point: Applicati Use Network-Layer Differentiated Services Code Point Point: Applicati
ons can expose their delivery expectations to the network by ons can expose their delivery expectations to the network by
setting the Differentiated Services Code Point (DSCP) field of setting the Differentiated Services Code Point (DSCP) field of
IPv4 and IPv6 packets. This can be used to inform network-layer IPv4 and IPv6 packets. This can be used to inform network-layer
queuing and forwarding, and can also provide information on the queuing and forwarding, and can also provide information on the
relative importance of packet information collected by measurement relative importance of packet information collected by measurement
campaigns, but does not directly provide any performance data. campaigns, but does not directly provide performance data.
This field provides explicit information that can be used in place This field provides explicit information that can be used in place
of inferring traffic requirements (e.g., by inferring QoS of inferring traffic requirements (e.g., by inferring QoS
requirements from port information via a multi-field classifier). requirements from port information via a multi-field classifier).
The DSCP value can therefore impact the quality of experience for The DSCP value can therefore impact the quality of experience for
a flow. Observations of service performance need to consider this a 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.
Use of Explicit Congestion Marking: ECN [RFC3168] is an optional Use of Explicit Congestion Marking: ECN [RFC3168] is an optional
skipping to change at page 13, line 34 skipping to change at page 13, line 43
throughput, reduced delay, and other benefits when used over a throughput, reduced delay, and other benefits when used over a
path that includes equipment that supports an AQM method that path that includes equipment that supports an AQM method that
performs Congestion Experienced (CE) marking of IP packets performs Congestion Experienced (CE) marking of IP packets
[RFC8087]. [RFC8087].
ECN exposes the presence of congestion on a network path to the ECN exposes the presence of congestion on a network path to the
transport and network layer. The reception of CE-marked packets transport and network layer. The reception of CE-marked packets
can therefore be used to monitor the presence and estimate the can therefore be used to monitor the presence and estimate the
level of incipient congestion on the upstream portion of the path level of incipient congestion on the upstream portion of the path
from the point of observation (Section 2.5 of [RFC8087]). Because from the point of observation (Section 2.5 of [RFC8087]). Because
ECN marks carried in the IP protocol header, it is much easier to ECN marks are carried in the IP protocol header, it is much easier
measure ECN than metering packet loss. However, interpreting the to measure ECN than to measure packet loss. However, interpreting
marking behaviour (i.e., assessing congestion and diagnosing the marking behaviour (i.e., assessing congestion and diagnosing
faults) requires context from the transport layer (path RTT, faults) requires context from the transport layer (path RTT,
visibility of loss - that could be due to queue overflow, visibility of loss - that could be due to queue overflow,
congestion response, etc) [RFC7567]. congestion response, etc) [RFC7567].
Some ECN-capable network devices can provide richer (more frequent Some ECN-capable network devices can provide richer (more frequent
and fine-grained) indication of their congestion state. Setting and fine-grained) indication of their congestion state. Setting
congestion marks proportional to the level of congestion (e.g., congestion marks proportional to the level of congestion (e.g.,
Data Center TCP, DCTP [RFC8257], and Low Latency Low Loss Scalable Data Center TCP, DCTP [RFC8257], and Low Latency Low Loss Scalable
throughput, L4S, [I-D.ietf-tsvwg-l4s-arch]. throughput, L4S, [I-D.ietf-tsvwg-l4s-arch].
skipping to change at page 14, line 19 skipping to change at page 14, line 25
increases and new methods emerge [RFC7567] [RFC8087]. ECN- increases and new methods emerge [RFC7567] [RFC8087]. ECN-
monitoring is expected to become important as AQM is deployed that monitoring is expected to become important as AQM is deployed that
supports ECN [RFC8087]. supports ECN [RFC8087].
2.2. Transport Measurement 2.2. 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 transport can view and analyse. For most packets, this has been transport
layer, until the emergence of QUIC, with the obvious exception of layer, until the emergence of QUIC, with the obvious exception of
VPNs and IPsec. When encryption conceals more layers in a packet, Virtual Private Networks (VPNs) and IPsec.
people seeking understanding of the network operation need to rely
more on pattern inferences and other heuristics. The accuracy of When encryption conceals more layers in each packet, people seeking
measurements therefore suffers, as does the ability to investigate understanding of the network operation rely more on pattern
and troubleshoot interactions between different anomalies. For inferences and other heuristics reliance on pattern inferences and
example, the traffic patterns between a web server and a browser are accuracy suffers. For example, the traffic patterns between server
dependent on browser supplier and version, even use of the and browser are dependent on browser supplier and version, even when
application (e.g., web e-mail access). Even when measurement datasets the sessions use the same server application (e.g., web e-mail
are made available (e.g., from endpoints) additional metadata, such access). It remains to be seen whether more complex inferences can be
as the state of the network, is often required to interpret the data. mastered to produce the same monitoring accuracy [I-D.mm-wg-effect-
Collecting and coordinating such metadata is more difficult when the encrypt].
observation point is at a different location to the bottleneck/device
under evaluation. When measurement datasets are made available by servers or client
endpoints, additional metadata, such as the state of the network, is
often required to interpret this data. Collecting and coordinating
such metadata is more difficult when the observation point is at a
different location to the bottleneck/device under evaluation.
Packet sampling techniques can be used to scale the processing Packet sampling techniques can be used to scale the processing
involved in observing packets on high rate links. This exports only involved in observing packets on high rate links. This exports only
the packet header information of (randomly) selected packets. The 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
relatively easy to manage, a device with more complexity demands relatively easy to manage, a device with more complexity demands
understanding of the choice of many system parameters. This level of understanding of the choice of many system parameters. This level of
complexity exists when several network methods are combined. complexity exists when several network methods are combined.
skipping to change at page 15, line 17 skipping to change at page 15, line 18
length (CODEL), flow-scheduling, and a starvation prevention length (CODEL), flow-scheduling, and a starvation prevention
mechanism. Usually such algorithms are designed to be self-tuning, mechanism. Usually such algorithms are designed to be self-tuning,
but current methods typically employ heuristics that can result in but current methods typically employ heuristics that can result in
more loss under certain path conditions (e.g., large RTT, effects of more loss under certain path conditions (e.g., large RTT, effects of
multiple bottlenecks [RFC7567]). multiple bottlenecks [RFC7567]).
In-network measurements can distinguish between upstream and In-network measurements can distinguish between upstream and
downstream metrics with respect to a measurement point. These are downstream metrics with respect to a measurement point. These are
particularly useful for locating the source of problems or to assess particularly useful for locating the source of problems or to assess
the performance of a network segment or a particular device the performance of a network segment or a particular device
configuration. configuration. By correlating observations of headers at multiple
points along the path (e.g., at the ingress and egress of a network
By correlating observations of headers at multiple points along the segment), an observer can determine the contribution of a portion of
path (e.g., at the ingress and egress of a network segment), an the path to an observed metric (to locate a source of delay, jitter,
observer can determine the contribution of a portion of the path to loss, reordering, congestion marking, etc.).
an observed metric (to locate a source of delay, jitter, loss,
reordering, congestion marking, etc.).
2.2.2. Use by Operators to Plan and Provision Networks 2.2.2. Use by Operators to Plan and Provision Networks
Traffic measurements (e.g., traffic volume, loss, latency) is used by Traffic measurements (e.g., traffic volume, loss, latency) is used by
operators to help plan deployment of new equipment and configurations operators to help plan deployment of new equipment and configurations
in their networks. Data is also important to equipment vendors who in their networks. Data is also important to equipment vendors who
need to understand traffic trends and patterns of usage as inputs to need to understand traffic trends and patterns of usage as inputs to
decisions about planning products and provisioning for new decisions about planning products and provisioning for new
deployments. This measurement information can also be correlated deployments. This measurement information can also be correlated
with billing information when this is also collected by an operator. with billing information when this is also collected by an operator.
A network operator supporting traffic that uses transport header A network operator supporting traffic that uses transport header
encryption may not have access to per-flow measurement data. Trends encryption may not have access to per-flow measurement data. Trends
in aggregate traffic can be observed and can be related this to the in aggregate traffic can be observed and can be related to the
endpoint addresses being used, but it may not be possible to endpoint addresses being used, but it may not be possible to
correlate patterns in measurements with changes in transport correlate patterns in measurements with changes in transport
protocols (e.g., the impact of changes in introducing a new transport protocols (e.g., the impact of changes in introducing a new transport
protocol mechanism). This increases the dependency on other indirect protocol mechanism). This increases the dependency on other indirect
sources of information to inform planning and provisioning. sources of information to inform planning and provisioning.
2.2.3. Service Performance Measurement 2.2.3. 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
skipping to change at page 16, line 24 skipping to change at page 16, line 24
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., to
prevent flows from acquiring excessive network capacity under severe prevent flows from acquiring excessive network capacity under severe
congestion) by deploying rate-limiters, traffic shaping or network congestion) by deploying rate-limiters, traffic shaping or network
transport circuit breakers [RFC8084]. transport circuit breakers [RFC8084].
Congestion Control Compliance of Traffic: Congestion control is a key Congestion Control Compliance of Traffic: Congestion control is a key
transport function. Many network operators implicitly accept that transport function [RFC2914]. Many network operators implicitly
TCP traffic to comply with a behaviour that is acceptable for use accept that TCP traffic to comply with a behaviour that is
in the shared Internet. TCP algorithms have been continuously acceptable for use in the shared Internet. TCP algorithms have
improved over decades, and they have reached a level of efficiency been continuously improved over decades, and they have reached a
and correctness that custom application-layer mechanisms will level of efficiency and correctness that custom application-layer
struggle to easily duplicate [RFC8085]. mechanisms will struggle to easily duplicate [RFC8085].
A standards-compliant TCP stack provides congestion control may A standards-compliant TCP stack provides congestion control may
therefore be judged safe for use across the Internet. therefore be judged safe for use across the Internet.
Applications developed on top of well-designed transports can be Applications developed on top of well-designed transports can be
expected to appropriately control their network usage, reacting expected to appropriately control their network usage, reacting
when the network experiences congestion, by back-off and reduce when the network experiences congestion, by back-off and reduce
the load placed on the network. This is the normal expected the load placed on the network. This is the normal expected
behaviour for TCP and SCTP. behaviour for IETF-specified transport (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 understanding of the dynamics of a flow and its network can gain understanding of the dynamics of a flow and its
congestion control behaviour. Analysing observed packet sequence congestion control behaviour. Analysing observed packet sequence
numbers can be used to help build confidence that an application numbers can be used to help build confidence that an application
flow backs-off its share of the network load in the face of flow backs-off its share of the network load in the face of
persistent congestion, and hence to understand whether the persistent congestion, and hence to understand whether the
behaviour is appropriate for sharing limited network capacity. behaviour is appropriate for sharing limited network capacity.
For example, it is common to visualise plots of TCP sequence For example, it is common to visualise plots of TCP sequence
numbers versus time for a flow to understand how a flow shares numbers versus time for a flow to understand how a flow shares
available capacity, deduce its dynamics in response to congestion, available capacity, deduce its dynamics in response to congestion,
etc. etc.
Congestion Control Compliance for UDP traffic UDP provides a minimal Congestion Control Compliance for UDP traffic UDP provides a minimal
message-passing transport that has no inherent congestion control message-passing datagram transport that has no inherent congestion
mechanisms. Because congestion control is critical to the stable control mechanisms. Because congestion control is critical to the
operation of the Internet, applications and other protocols that stable operation of the Internet, applications and other protocols
choose to use UDP as a transport are required to employ mechanisms that choose to use UDP as a transport are required to employ
to prevent congestion collapse, avoid unacceptable contributions mechanisms to prevent congestion collapse, avoid unacceptable
to jitter/latency, and to establish an acceptable share of contributions to jitter/latency, and to establish an acceptable
capacity with concurrent traffic [RFC8085]. share of capacity with concurrent traffic [RFC8085].
A network operator needs tools to understand if UDP flows comply A network operator needs tools to understand if datagram flows
with congestion control expectations and therefore whether there comply with congestion control expectations and therefore whether
is a need to deploy methods such as rate-limiters, transport there is a need to deploy methods such as rate-limiters, transport
circuit breakers or other methods to enforce acceptable usage for circuit breakers or other methods to enforce acceptable usage for
the offered service. the offered service.
UDP flows that expose a well-known header by specifying the format UDP flows that expose a well-known header by specifying the format
of header fields can allow information to be observed to gain of header fields can allow information to be observed to gain
understanding of the dynamics of a flow and its congestion control understanding of the dynamics of a flow and its congestion control
behaviour. For example, tools exist to monitor various aspects of behaviour. For example, tools exist to monitor various aspects of
the RTP and RTCP header information of real-time flows (see the RTP and RTCP header information of real-time flows (see
Section 2.1.2. Section 2.1.2.
skipping to change at page 17, line 39 skipping to change at page 18, line 8
Transport header information is useful for a variety of operational Transport header information is useful for a variety of operational
tasks [I-D.mm-wg-effect-encrypt]: to diagnose network problems, tasks [I-D.mm-wg-effect-encrypt]: to diagnose network problems,
assess performance, capacity planning, management of denial of assess performance, capacity planning, management of denial of
service threats, and responding to user performance questions. These service threats, and responding to user performance questions. These
tasks seldom involve the need to determine the contents of the tasks seldom involve the need to determine the contents of the
transport payload, or other application details. transport payload, or other application details.
A network operator supporting traffic that uses transport header A network operator supporting traffic that uses transport header
encryption can see only encrypted transport headers. This prevents encryption can see only encrypted transport headers. This prevents
deployment of performance measurement tools that rely on transport deployment of performance measurement tools that rely on transport
protocol information. Choosing to encrypt all information may be protocol information. Choosing to encrypt all information may reduce
expected to reduce the ability for networks to "help" (e.g., in the ability for networks to "help" (e.g., in response to tracing
response to tracing issues, making appropriate Quality of Service, issues, making appropriate QoS decisions). For some this will be
QoS, decisions). For some this will be blessing, for others it may be blessing, for others it may be a curse. For example, operational
a curse. For example, operational performance data about encrypted performance data about encrypted flows needs to be determined by
flows needs to be determined by traffic pattern analysis, rather than traffic pattern analysis, rather than relying on traditional tools.
relying on traditional tools. This can impact the ability of the This can impact the ability of the operator to respond to faults, it
operator to respond to faults, it could require reliance on endpoint could require reliance on endpoint diagnostic tools or user
diagnostic tools or user involvement in diagnosing and involvement in diagnosing and troubleshooting unusual use cases or
troubleshooting unusual use cases or non-trivial problems. A key non-trivial problems. A key need here is for tools to provide useful
need here is that tools need to provide useful information during information during network anomalies (e.g., significant reordering,
network anomalies (e.g., significant reordering, high or intermittent high or intermittent loss). Although many network operators utilise
loss). Although many network operators utilise transport information transport information as a part of their operational practice, the
as a part of their operational practice, the network will not break network will not break because transport headers are encrypted, and
because transport headers are encrypted. this may require alternative tools may need to be developed and
deployed.
2.3.1. Examples of measurements 2.3.1. Examples of measurements
Future versions of this document may provide more about existing
tooling at Network Operations Centres that rely upon observing
transport layer header information.
Debugging and diagnosing the root causes of faults concern particular Measurements can be used to monitor the health of a portion of the
users traffic is an activity that may depend on connection Internet, to provide early warning of the need to take action. They
information from the protocol - In some case, this may involve active can assist in debugging and diagnosing the root causes of faults that
injection of test traffic to complete a measurement. Most operators concern a particular user's traffic. They can also be used to
do not have access to user equipment. There may also be costs support post-mortem inverstigation after an anompoly to determine the
associated with running such tests (e.g., the implications of root cause of a problem.
bandwidth tests in a mobile network are obvious). Some active
measurements (e.g., response under load or particular workloads) may In some case, measurements may involve active injection of test
traffic to complete a measurement. However, most operators do not
have access to user equipment, and injection of test traffic may be
associated with costs in running such tests (e.g., the implications
of bandwidth tests in a mobile network are obvious). Some active
measurements (e.g., response under load or particular workloads)
perturb other traffic, and could require dedicated access to the perturb other traffic, and could require dedicated access to the
network segment. An alternative approach is to use in-network network segment. An alternative approach is to use in-network
techniques that observe transport packet headers in operational techniques that observe transport packet headers in operational
networks to make the measurements. networks to make the measurements.
in other cases, measurement involves dissecting traffic flows. The In other cases, measurement involves dissecting network traffic
observed transport layer information can help identify whether the flows. The observed transport layer information can help identify
link/network tuning is effective and alert to potential problems that whether the link/network tuning is effective and alert to potential
can be hard to derive from link or device measurements alone. The problems that can be hard to derive from link or device measurements
design trade-offs for radio networks are often very different to alone. The design trade-offs for radio networks are often very
those of wired networks. A radio-based network (e.g., cellular different to those of wired networks. A radio-based network (e.g.,
mobile, enterprise WiFi, satellite access/back-haul, point-to-point cellular mobile, enterprise WiFi, satellite access/back-haul, point-
radio) has the complexity of a subsystem that performs radio resource to-point radio) has the complexity of a subsystem that performs radio
management - with direct impact on the available capacity, and resource management,s with direct impact on the available capacity,
potentially loss/reordering of packets. The impact of the pattern of and potentially loss/reordering of packets. The impact of the
loss and congestion, differs for different traffic types, correlation pattern of loss and congestion, differs for different traffic types,
with propagation and interference can all have significant impact on correlation with propagation and interference can all have
the cost and performance of a provided service. The need for this significant impact on the cost and performance of a provided service.
type of information is expected to increase as operators bring The need for this type of information is expected to increase as
together heterogeneous types of network equipment and seek to deploy operators bring together heterogeneous types of network equipment and
opportunistic methods to access radio spectrum. seek to deploy opportunistic methods to access radio spectrum.
XXX Note: The authors are looking for contributions that say more
about the things people are currently doing with exposed transport
fields and what problems they are trying to solve, or how they use
the information they derive. How problematic is new tools to follow-
up. Examples could include: Health monitoring; anomoly/DoS
detection; Capacity planning, etc XXX
2.4. Observing Headers to Implement Network Policy 2.4. Observing Headers to Implement Network Policy
Information from the transport protocol can be used by a multi-field Information from the transport protocol can be used by a multi-field
classifier as a part of policy framework. Policies are commonly used classifier as a part of policy framework. Policies are commonly used
for QoS management for resource-constrained networks and by firewalls for management of the QoS or Quality of Experience (QoE) in resource-
that use the information to implement access rules. Traffic that constrained networks and by firewalls that use the information to
cannot be classified, will typically receive a default treatment. implement access rules. Traffic that cannot be classified, will
typically receive a default treatment.
3. Encryption and Authentication of Transport Headers 3. Encryption and Authentication of Transport Headers
End-to-end encryption can be applied at various protocol layers. It End-to-end encryption can be applied at various protocol layers. It
can be applied above the transport to encrypt the transport payload. can be applied above the transport to encrypt the transport payload.
Encryption methods can hide information from an eavesdropper in the Encryption methods can hide information from an eavesdropper in the
network. Encryption can also help protect the privacy of a user, by network. Encryption can also help protect the privacy of a user, by
hiding data relating to user/device identity or location. Neither an hiding data relating to user/device identity or location. Neither an
integrity check nor encryption methods prevent traffic analysis, and integrity check nor encryption methods prevent traffic analysis, and
usage needs to reflect that profiling of users, identification of usage needs to reflect that profiling of users, identification of
location and fingerprinting of behaviour can take place even on location and fingerprinting of behaviour can take place even on
encrypted traffic flows. encrypted traffic flows.
skipping to change at page 19, line 14 skipping to change at page 19, line 43
End-to-end encryption can be applied at various protocol layers. It End-to-end encryption can be applied at various protocol layers. It
can be applied above the transport to encrypt the transport payload. can be applied above the transport to encrypt the transport payload.
Encryption methods can hide information from an eavesdropper in the Encryption methods can hide information from an eavesdropper in the
network. Encryption can also help protect the privacy of a user, by network. Encryption can also help protect the privacy of a user, by
hiding data relating to user/device identity or location. Neither an hiding data relating to user/device identity or location. Neither an
integrity check nor encryption methods prevent traffic analysis, and integrity check nor encryption methods prevent traffic analysis, and
usage needs to reflect that profiling of users, identification of usage needs to reflect that profiling of users, identification of
location and fingerprinting of behaviour can take place even on location and fingerprinting of behaviour can take place even on
encrypted traffic flows. encrypted traffic flows.
One motive to use encryption is a response to perceptions that the There are several motivations:
network has become ossified by over-reliance on middleboxes that
prevent new protocols and mechanisms from being deployed. This has
lead to a common perception that there is too much "manipulation" of
protocol headers within the network, and that designing to deploy in
such networks is preventing transport evolution. In the light of
this, a method that authenticates transport headers may help improve
the pace of transport development, by eliminating the need to always
consider deployed middleboxes [I-D.trammell-plus-abstract-mech], or
potentially to only explicitly enable middlebox use for particular
paths with particular middleboxes that are deliberately deployed to
realise a useful function for the network and/or users[RFC3135].
Another motivation stems from increased concerns about privacy and o One motive to use encryption is a response to perceptions that the
surveillance. Some Internet users have valued the ability to protect network has become ossified by over-reliance on middleboxes that
identity, user location, and defend against traffic analysis, and prevent new protocols and mechanisms from being deployed. This
have used methods such as IPsec ESP. Revelations about the use of has lead to a perception that there is too much "manipulation" of
pervasive surveillance [RFC7624] have, to some extent, eroded trust protocol headers within the network, and that designing to deploy
in the service offered by network operators, and following the in such networks is preventing transport evolution. In the light
Snowden revelation in the USA in 2013 has led to an increased desire of this, a method that authenticates transport headers may help
for people to employ encryption to avoid unwanted "eavesdropping" on improve the pace of transport development, by eliminating the need
their communications. Whatever the reasons, there are now activities to always consider deployed middleboxes [I-D.trammell-plus-
in the IETF to design new protocols that may include some form of abstract-mech], or potentially to only explicitly enable middlebox
transport header encryption (e.g., QUIC [I-D.ietf-quic-transport]). use for particular paths with particular middleboxes that are
deliberately deployed to realise a useful function for the network
and/or users[RFC3135].
o Another motivation stems from increased concerns about privacy and
surveillance. Some Internet users have valued the ability to
protect identity, user location, and defend against traffic
analysis, and have used methods such as IPsec ESP. Revelations
about the use of pervasive surveillance [RFC7624] have, to some
extent, eroded trust in the service offered by network operators,
and following the Snowden revelation in the USA in 2013 has led to
an increased desire for people to employ encryption to avoid
unwanted "eavesdropping" on their communications. Concerns have
also been voiced about the addition of information to packets by
third parties to provide analytics, customization, advertising,
cross-site tracking of users, to bill the customer, or to
selectively allow or block content. Whatever the reasons, there
are now activities in the IETF to design new protocols that may
include some form of transport header encryption (e.g., QUIC [I-D
.ietf-quic-transport]).
Authentication methods (that provide integrity checks of protocols Authentication methods (that provide integrity checks of protocols
fields) have also been specified at the network layer, and this also fields) have also been specified at the network layer, and this also
protects transport header fields. The network layer itself carries protects transport header fields. The network layer itself carries
protocol header fields that are increasingly used to help forwarding protocol header fields that are increasingly used to help forwarding
decisions reflect the need of transport protocols, such the IPv6 Flow decisions reflect the need of transport protocols, such as the IPv6
Label [RFC6437], the DSCP and ECN. Flow Label [RFC6437], the DSCP and ECN.
The use of transport layer authentication and encryption exposes a The use of transport layer authentication and encryption exposes a
tussle between middlebox vendors, operators, applications developers tussle between middlebox vendors, operators, applications developers
and users. and users.
o On the one hand, future Internet protocols that enable large-scale o On the one hand, future Internet protocols that enable large-scale
encryption assist in the restoration of the end-to-end nature of encryption assist in the restoration of the end-to-end nature of
the Internet by returning complex processing to the endpoints, the Internet by returning complex processing to the endpoints,
since middleboxes cannot modify what they cannot see. since middleboxes cannot modify what they cannot see.
skipping to change at page 21, line 22 skipping to change at page 22, line 15
3.4. Authenticating Transport Information and Selectively Encrypting 3.4. Authenticating Transport Information and Selectively Encrypting
the Transport Header the Transport Header
A transport protocol design can encrypt selected header fields, while A transport protocol design can encrypt selected header fields, while
also choosing to authenticate fields in the transport header. This also choosing to authenticate fields in the transport header. This
allows specific transport header fields to be made observable by allows specific transport header fields to be made observable by
network devices. End-to end integrity checks can prevent an endpoint network devices. End-to end integrity checks can prevent an endpoint
from undetected modification of the immutable transport headers. from undetected modification of the immutable transport headers.
The choice of which fields to expose and which to encrypt is a design
choice for the transport protocol. Any selective encryption method
requires trading two conflicting goals for a transport protocol
designer to decide which header fields to encrypt. On the one hand,
security work typically employs a design technique that seeks to
expose only what is needed. On the other hand, there may be
performance and operational benefits in exposing selected information
to network tools.
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 may be authenticated End-to-End across a path. fields that may 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.
3.5. Optional Encryption of Header Information 3.5. Optional Encryption of Header Information
skipping to change at page 21, line 52 skipping to change at page 22, line 36
There are implications to the use of optional header encryption in There are implications to the use of optional header encryption in
the design of a transport protocol, where support of optional the design of a transport protocol, where support of optional
mechanisms can increase the complexity of the protocol and its mechanisms can increase the complexity of the protocol and its
implementation and in the management decisions that are required to implementation and in the management decisions that are required to
use variable format fields. Instead, fields of a specific type ought use variable format fields. Instead, fields of a specific type ought
to always be sent with the same level of confidentiality or integrity to always be sent with the same level of confidentiality or integrity
protection. protection.
4. Addition of Transport Information to Network-Layer Protocol Headers 4. Addition of Transport Information to Network-Layer Protocol Headers
The transport information can be made visible in a network-layer Transport protocol information can be made visible in a network-layer
header. This has the advantage that this information can then be header. This has the advantage that this information can then be
observed by in-network devices. This has the advantage that a single observed by in-network devices. This has the advantage that a single
header can support all transport protocols, but there may also be header can support all transport protocols, but there may also be
less desirable implications of separating the operation of the less desirable implications of separating the operation of the
transport protocol from the measurement framework. transport protocol from the measurement framework.
Some measurements may be made by adding additional protocol headers Some measurements may be made by adding additional protocol headers
carrying operations, administration and management (OAM) information carrying operations, administration and management (OAM) information
to packets at the ingress to a maintenance domain (e.g., an Ethernet to packets at the ingress to a maintenance domain (e.g., an Ethernet
protocol header with timestamps and sequence number information using protocol header with timestamps and sequence number information using
skipping to change at page 22, line 28 skipping to change at page 23, line 19
Another example of a network-layer approach is the IPv6 Performance Another example of a network-layer approach is the IPv6 Performance
and Diagnostic Metrics (PDM) Destination Option [I-D.ietf-ippm-6man- and Diagnostic Metrics (PDM) Destination Option [I-D.ietf-ippm-6man-
pdm-option]. This allows a sender to optionally include a pdm-option]. This allows a sender to optionally include a
destination option that caries header fields that can be used to destination option that caries header fields that can be used to
observe timestamps and packet sequence numbers. This information observe timestamps and packet sequence numbers. This information
could be authenticated by receiving transport endpoints when the could be authenticated by receiving transport endpoints when the
information is added at the sender and visible at the receiving information is added at the sender and visible at the receiving
endpoint, although methods to do this have not currently been endpoint, although methods to do this have not currently been
proposed. This method needs to be explicitly enabled at the sender. proposed. This method needs to be explicitly enabled at the sender.
It can be undesirable to rely on methods requiring options or It can be undesirable to rely on methods requiring the presence of
extension headers. IPv4 network options are often not supported (or network options or extension headers. IPv4 network options are often
are carried on a slower processing path) and some IPv6 networks are not supported (or are carried on a slower processing path) and some
also known to drop packets that set an IPv6 header extension (e.g., IPv6 networks are also known to drop packets that set an IPv6 header
[RFC7872]). Another disadvantage is that protocols that separately extension (e.g., [RFC7872]). Another disadvantage is that protocols
expose header information do not necessarily have an advantage to that separately expose header information do not necessarily have an
expose the information that is utilised by the protocol itself, and advantage to expose the information that is utilised by the protocol
could manipulate this header information to gain an advantage from itself, and could manipulate this header information to gain an
the network. advantage from the network.
5. Implications of Protecting the Transport Headers 5. Implications of Protecting the Transport Headers
The choice of which fields to expose and which to encrypt is a design
choice for the transport protocol. Any selective encryption method
requires trading two conflicting goals for a transport protocol
designer to decide which header fields to encrypt. Security work
typically employs a design technique that seeks to expose only what
is needed. However, there can be performance and operational
benefits in exposing selected information to network tools.
This section explores key implications of working with encrypted This section explores key implications of working with encrypted
transport protocols. transport protocols.
5.1. Independent Measurement 5.1. Independent Measurement
Independent observation by multiple actors is important for Independent observation by multiple actors is important for
scientific analysis. Encrypting transport header encryption changes scientific analysis. Encrypting transport header encryption changes
the ability for other actors to collect and independently analyse the ability for other actors to collect and independently analyse
data. Internet transport protocols employ a set of mechanisms. Some data. Internet transport protocols employ a set of mechanisms. Some
of these need to work in cooperation with the network layer - loss of these need to work in cooperation with the network layer - loss
detection and recovery, congestion detection and congestion control, detection and recovery, congestion detection and congestion control,
some of these need to work only End-to-End (e.g., parameter some of these need to work only End-to-End (e.g., parameter
negotiation, flow-control). negotiation, flow-control).
When encryption conceals information in the transport header, it When encryption conceals information in the transport header, it
could be possible for an applications to provide summary data on could be possible for an applications to provide summary data on
performance and usage of the network. This data could be made performance and usage of the network. This data could be made
available to other actors. However, this data needs to contain available to other actors. However, this data needs to contain
sufficient detail to understand (and possibly reconstruct the network sufficient detail to understand (and possibly reconstruct the network
traffic pattern for further testing) and to be correlated with the traffic pattern for further testing) and to be correlated with the
configuration of the network paths being measured. Sharing configuration of the network paths being measured.
information between actors needs also to consider the privacy of the
user and the incentives for providing accurate and detailed Sharing information between actors needs also to consider the privacy
of the user and the incentives for providing accurate and detailed
information. Protocols that expose the state information used by the information. Protocols that expose the state information used by the
transport protocol in their header information (e.g., timestamps used transport protocol in their header information (e.g., timestamps used
to calculate the RTT, packet numbers used to asses congestion and to calculate the RTT, packet numbers used to asses congestion and
requests for retransmission) provide an incentive for the sending requests for retransmission) provide an incentive for the sending
endpoint to provide correct information, increasing confidence that endpoint to provide correct information, increasing confidence that
the observer understands the transport interaction with the network. the observer understands the transport interaction with the network.
This becomes important when considering changes to transport This becomes important when considering changes to transport
protocols, changes in network infrastructure, or the emergence of new protocols, changes in network infrastructure, or the emergence of new
traffic patterns. traffic patterns.
skipping to change at page 24, line 6 skipping to change at page 25, line 15
5.3. Accountability and Internet Transport Protocols 5.3. Accountability and Internet Transport Protocols
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, and where needed to flows from acquiring excessive network capacity, and where needed to
deploy appropriate tools Section 2.2.4. Obfuscating or hiding this deploy appropriate tools Section 2.2.4. Obfuscating or hiding this
information using encryption is expected to lead operators and information using encryption is expected to lead operators and
maintainers of middleboxes (firewalls, etc.) to seek other methods to maintainers of middleboxes (firewalls, etc.) to seek other methods to
classify and mechanisms to condition network traffic. classify and mechanisms to condition network traffic.
A lack of data seems likely to reduce the level of precision with A lack of data reduces the level of precision with which mechanisms
which these mechanisms are applied, and this needs to be considered are applied, and this needs to be considered when evaluating the
when evaluating the impact of designs for transport encryption. This impact of designs for transport encryption. This could lead to
could lead to increased use of rate limiting, circuit breaker increased use of rate limiting, circuit breaker techniques [RFC8084],
techniques [RFC8084], or even blocking of uncharacterised traffic. or even blocking of uncharacterised traffic. This would hinder
This would hinder deployment of new mechanisms and/or protocols. deployment of new mechanisms and/or protocols.
5.4. Impact on Research, Development and Deployment 5.4. Impact on Research, Development and Deployment
There are both opportunities and also challenges to the design, The majority of present Internet applications use two well-known
evaluation and deployment of new transport protocol mechanisms. transport protocols: e.g., TCP and UDP. Although TCP represents the
majority of current traffic, some important real-time applications
use UDP, and much of this traffic utilises RTP format headers in the
payload of the UDP datagram. Since these protocol headers have been
fixed for decades, a range of tools and analysis methods have became
common and well-understood. Over this period, the transport protocol
headers have mostly changed slowly, and so also the need to develop
tools track new versions of the protocol.
Integrity checks can avoiding network devices undetected modification Looking ahead, there will be a need to update these protocols and to
of protocols, whereas encryption and obfuscation can prevent these develop and deploy new transport mechanisms and protocols. There are
headers being utilised by network devices. This provides greater both opportunities and also challenges to the design, evaluation and
freedom to update the protocols and can therefore ease deployment of new transport protocol mechanisms.
experimentation with new techniques and their final deployment in
endpoints.
Measurement data is increasingly being used to inform design Integrity checks can undetected modification of protocol fields by
decisions in networking research, during development of new network devices, whereas encryption and obfuscation can further
prevent these headers being utilised by network devices. Hiding
headers can therefore provide the opportunity for greater freedom to
update the protocols and can ease experimentation with new techniques
and their final deployment in endpoints.
Hiding headers can limit the ability to measure and characterise
traffic. Measurement data is increasingly being used to inform
design decisions in networking research, during development of new
mechanisms and protocols and in standardisation. Measurement has a mechanisms and protocols and in standardisation. Measurement has a
critical role in the design of transport protocol mechanisms and critical role in the design of transport protocol mechanisms and
their acceptance by the wider community (e.g., as a method to judge their acceptance by the wider community (e.g., as a method to judge
the safety for Internet deployment). Observation of pathologies are the safety for Internet deployment). Observation of pathologies are
also important in understanding the interactions between cooperating also important in understanding the interactions between cooperating
protocols and network mechanism, the implications of sharing capacity protocols and network mechanism, the implications of sharing capacity
with other traffic and the impact of different patterns of usage. with other traffic and the impact of different patterns of usage.
Attention needs to be paid to the expected scale of deployment of new Evolution and the ability to understand (measure) the impact need to
protocols and protocol mechanisms. Whatever the mechanism, proceed hand-in-hand. Attention needs to be paid to the expected
experience has shown that it is often difficult to correctly scale of deployment of new protocols and protocol mechanisms.
implement combination of mechanisms [RFC8085]. These mechanisms Whatever the mechanism, experience has shown that it is often
therefore typically evolve as a protocol matures, or in response to difficult to correctly implement combination of mechanisms [RFC8085].
changes in network conditions, changes in network traffic or changes These mechanisms therefore typically evolve as a protocol matures, or
to application usage. in response to changes in network conditions, changes in network
traffic or changes to application usage.
New transport protocol formats are expected to facilitate an New transport protocol formats are expected to facilitate an
increased pace of transport evolution, and with it the possibility to increased pace of transport evolution, and with it the possibility to
experiment with and deploy a wide range of protocol mechanisms. experiment with and deploy a wide range of protocol mechanisms.
There has been recent interest in a wide range of new transport There has been recent interest in a wide range of new transport
methods, e.g., Larger Initial Window, Proportional Rate Reduction methods, e.g., Larger Initial Window, Proportional Rate Reduction
(PRR), congestion control methods based on measuring bottleneck (PRR), congestion control methods based on measuring bottleneck
bandwidth and round-trip propagation time, the introduction of AQM bandwidth and round-trip propagation time, the introduction of AQM
techniques and new forms of ECN response (e.g., DCTP, and methods techniques and new forms of ECN response (e.g., Data Centre TCP,
proposed for L4S).The growth and diversity of applications and DCTP, and methods proposed for L4S).The growth and diversity of
protocols using the Internet also continues to expand. For each new applications and protocols using the Internet also continues to
method or application it is desirable to build a body of data expand. For each new method or application it is desirable to build
reflecting its behaviour under a wide range of deployment scenarios, a body of data reflecting its behaviour under a wide range of
traffic load, and interactions with other deployed/candidate methods. deployment scenarios, traffic load, and interactions with other
deployed/candidate methods.
Open standards motivate a desire for this evaluation to include Open standards motivate a desire for this evaluation to include
independent observation and evaluation of performance data, which in independent observation and evaluation of performance data, which in
turn suggests control over where and when measurement samples are turn suggests control over where and when measurement samples are
collected. This requires consideration of the appropriate balance collected. This requires consideration of the appropriate balance
between encrypting all and no transport information. between encrypting all and no transport information.
6. Conclusions 6. Conclusions
XXX Notes for a draft conclusion XXX The majority of present Internet applications use two well-known
transport protocols: e.g., TCP and UDP. Although TCP represents the
The majority of traffic sent by the present Internet uses two well- majority of current traffic, some important real-time applications
known transport protocols: e.g., TCP and UDP. have used UDP, and much of this traffic utilises RTP format headers
in the payload of the UDP datagram. Since these protocol headers
Although TCP represents the majority of current traffic, some have been fixed for decades, a range of tools and analysis methods
important real-time applications have used UDP, and much of this have became common and well-understood. Over this period, the
traffic utilises RTP format headers in the payload of the UDP data. transport protocol headers have mostly changed slowly, and so also
Since these protocol headers have been fixed for decades, a range of the need to develop tools track new versions of the protocol.
tools and analysis methods have became common and well-understood.
Over this period, the transport protocol headers have mostly changed
slowly, and so also the need to develop tools track new versions of
the protocol.
Encryption (confidentiality and strong integrity checks) have Confidentiality and strong integrity checks have properties that are
properties that are being incorporated into new protocols and which being incorporated into new protocols and which have important
have important benefits. The pace of development of transports using benefits. The pace of development of transports using the WebRTC
the WebRTC data channel and the rapid deployment of QUIC prototype data channel and the rapid deployment of QUIC prototype transports
transports can both be attributed to using a combination of UDP can both be attributed to using a combination of UDP transport and
transport and encryption of the UDP payload. confidentiality of the UDP payload.
The traffic that can be observed by devices in a network is a The traffic that can be observed by devices in a network is a
function of transport protocol design/options, network use, function of transport protocol design/options, network use,
applications and user characteristics. In general, when only a small applications and user characteristics. In general, when only a small
proportion of the traffic has a specific (different) characteristic. proportion of the traffic has a specific (different) characteristic.
Such traffic seldom leads to an operational issue although the Such traffic seldom leads to an operational issue although the
ability to measure and monitor it is less. The desire to understand ability to measure and monitor it is less. The desire to understand
the traffic and protocol interactions typically grows as the the traffic and protocol interactions typically grows as the
proportion of traffic increases in volume. The challenges increase proportion of traffic increases in volume. The challenges increase
when multiple instances of an evolving protocol contribute to the when multiple instances of an evolving protocol contribute to the
skipping to change at page 26, line 44 skipping to change at page 28, line 25
protocol information (preventing observation within the network). protocol information (preventing observation within the network).
The transport information can be used by operators to provide The transport information can be used by operators to provide
troubleshooting, easement and any necessary functions for the troubleshooting, easement and any necessary functions for the
class of traffic (priority, retransmission, reordering, circuit class of traffic (priority, retransmission, reordering, circuit
breakers, etc). breakers, etc).
o An alternative scenario adopts different design goals, with a o An alternative scenario adopts different design goals, with a
different outcome. A protocol that encrypts all header different outcome. A protocol that encrypts all header
information forces network operators to act independently from information forces network operators to act independently from
apps/transport developments to provide the transport information apps/transport developments to provide the transport information
they need. A range of approaches may proliferate - as in current they need. A range of approaches may proliferate, as in current
networks, operators can add a shim header to each packet as a flow networks, operators can add a shim header to each packet as a flow
as it crosses the network ; other operators/managers could develop as it crosses the network; other operators/managers could develop
heuristics and pattern recognition to derive information that heuristics and pattern recognition to derive information that
classifies flows and estimates quality metrics for the service classifies flows and estimates quality metrics for the service
being used; some could decide to rate-limit or block traffic until being used; some could decide to rate-limit or block traffic until
new tooling is in place. In many cases, the derived information new tooling is in place. In many cases, the derived information
can be used by operators to provide necessary functions for the can be used by operators to provide necessary functions
class of traffic (priority, retransmission, reordering, circuit appropriate to the class of traffic (priority, retransmission,
breakers, etc). Troubleshooting, and measurement becomes more reordering, circuit breakers, etc). Troubleshooting, and
difficult or could require additional information. In some cases, measurement becomes more difficult, and more diverse. This could
operators might need access to keying information to interpret require additional information beyond that visible in the packet
encrypted data that they observe. Some use cases could demand use header and. In some cases, operators might need access to keying
of transports that do not use encryption. information to interpret encrypted data that they observe. Some
use cases could demand use of transports that do not use
encryption.
The outcome could have significant implications on the way the The outcome could have significant implications on the way the
Internet architecture develops. It exposes a risk that significant Internet architecture develops. It exposes a risk that significant
actors (e.g., developers and transport designers) achieve more actors (e.g., developers and transport designers) achieve more
control of the way in which the Internet architecture develops.In control of the way in which the Internet architecture develops.In
particular, there is a possibility that designs could evolve to particular, there is a possibility that designs could evolve to
significantly benefit of customers for a specific vendor, and that significantly benefit of customers for a specific vendor, and that
communities with very different network, applications or platforms communities with very different network, applications or platforms
could then suffer at the expense of benefits to their vendors own could then suffer at the expense of benefits to their vendors own
customer base. In such a scenario, there could be no incentive to customer base. In such a scenario, there could be no incentive to
skipping to change at page 28, line 19 skipping to change at page 30, line 4
rfc2119>. rfc2119>.
10.2. Informative References 10.2. Informative References
[I-D.dolson-plus-middlebox-benefits] [I-D.dolson-plus-middlebox-benefits]
Dolson, D., Snellman, J., Boucadair, M. and C. Jacquenet, Dolson, D., Snellman, J., Boucadair, M. and C. Jacquenet,
"Beneficial Functions of Middleboxes", Internet-Draft "Beneficial Functions of Middleboxes", Internet-Draft
draft-dolson-plus-middlebox-benefits-03, March 2017. draft-dolson-plus-middlebox-benefits-03, March 2017.
[I-D.ietf-aqm-codel] [I-D.ietf-aqm-codel]
Nichols, K., Jacobson, V., McGregor, A. and J. Jana, Nichols, K., Jacobson, V., McGregor, A. and J. Iyengar,
"Controlled Delay Active Queue Management", Internet-Draft "Controlled Delay Active Queue Management", Internet-Draft
draft-ietf-aqm-codel-00, October 2014. draft-ietf-aqm-codel-10, October 2017.
[I-D.ietf-aqm-fq-codel] [I-D.ietf-aqm-fq-codel]
Hoeiland-Joergensen, T., McKenney, P., Taht, D., Gettys, Hoeiland-Joergensen, T., McKenney, P.,
J. and E. Dumazet, "FlowQueue-Codel", Internet-Draft dave.taht@gmail.com, d., Gettys, J. and E. Dumazet, "The
draft-ietf-aqm-fq-codel-00, January 2015. FlowQueue-CoDel Packet Scheduler and Active Queue
Management Algorithm", Internet-Draft draft-ietf-aqm-fq-
codel-06, March 2016.
[I-D.ietf-aqm-pie] [I-D.ietf-aqm-pie]
Pan, R., Natarajan, P., Baker, F. and G. White, "PIE: A Pan, R., Natarajan, P., Baker, F. and G. White, "PIE: A
Lightweight Control Scheme To Address the Bufferbloat Lightweight Control Scheme To Address the Bufferbloat
Problem", Internet-Draft draft-ietf-aqm-pie-00, October Problem", Internet-Draft draft-ietf-aqm-pie-10, September
2014. 2016.
[I-D.ietf-ippm-6man-pdm-option] [I-D.ietf-ippm-6man-pdm-option]
Elkins, N., Hamilton, R. and m. mackermann@bcbsm.com, Elkins, N., Hamilton, R. and m. mackermann@bcbsm.com,
"IPv6 Performance and Diagnostic Metrics (PDM) Destination "IPv6 Performance and Diagnostic Metrics (PDM) Destination
Option", Internet-Draft draft-ietf-ippm-6man-pdm- Option", Internet-Draft draft-ietf-ippm-6man-pdm-
option-10, May 2017. option-13, June 2017.
[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. and d. daniel.bernier@bell.ca, "Data Fields P., Chang, R., daniel.bernier@bell.ca, d. and J. Lemon,
for In-situ OAM", Internet-Draft draft-ietf-ippm-ioam- "Data Fields for In-situ OAM", Internet-Draft draft-ietf-
data-01, October 2017. ippm-ioam-data-02, March 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", Internet-Draft draft-ietf-quic- and Secure Transport", Internet-Draft draft-ietf-quic-
transport-03, May 2017. transport-03, May 2017.
[I-D.ietf-tcpm-accurate-ecn] [I-D.ietf-tcpm-accurate-ecn]
Briscoe, B., Kuehlewind, M. and R. Scheffenegger, "More Briscoe, B., Kuehlewind, M. and R. Scheffenegger, "More
Accurate ECN Feedback in TCP", Internet-Draft draft-ietf- Accurate ECN Feedback in TCP", Internet-Draft draft-ietf-
tcpm-accurate-ecn-00, December 2015. tcpm-accurate-ecn-06, March 2018.
[I-D.ietf-tsvwg-l4s-arch] [I-D.ietf-tsvwg-l4s-arch]
Briscoe, B., Schepper, K. and M. Bagnulo, "Low Latency, Briscoe, B., Schepper, K. and M. Bagnulo, "Low Latency,
Low Loss, Scalable Throughput (L4S) Internet Service: Low Loss, Scalable Throughput (L4S) Internet Service:
Architecture", Internet-Draft draft-ietf-tsvwg-l4s- Architecture", Internet-Draft draft-ietf-tsvwg-l4s-
arch-00, May 2017. arch-01, October 2017.
[I-D.mm-wg-effect-encrypt] [I-D.mm-wg-effect-encrypt]
Moriarty, K. and A. Morton, "Effect of Pervasive Moriarty, K. and A. Morton, "Effects of Pervasive
Encryption on Operators", Internet-Draft draft-mm-wg- Encryption on Operators", Internet-Draft draft-mm-wg-
effect-encrypt-11, April 2017. effect-encrypt-24, March 2018.
[I-D.thomson-quic-grease]
Thomson, M., "More Apparent Randomization for QUIC",
Internet-Draft draft-thomson-quic-grease-00, December
2017.
[I-D.trammell-plus-abstract-mech] [I-D.trammell-plus-abstract-mech]
Trammell, B., "Abstract Mechanisms for a Cooperative Path Trammell, B., "Abstract Mechanisms for a Cooperative Path
Layer under Endpoint Control", Internet-Draft draft- Layer under Endpoint Control", Internet-Draft draft-
trammell-plus-abstract-mech-00, September 2016. trammell-plus-abstract-mech-00, September 2016.
[I-D.trammell-plus-statefulness] [I-D.trammell-plus-statefulness]
Kuehlewind, M., Trammell, B. and J. Hildebrand, Kuehlewind, M., Trammell, B. and J. Hildebrand,
"Transport-Independent Path Layer State Management", "Transport-Independent Path Layer State Management",
Internet-Draft draft-trammell-plus-statefulness-02, Internet-Draft draft-trammell-plus-statefulness-02,
skipping to change at page 29, line 45 skipping to change at page 31, line 37
Experimental Design, Implementation, and Policy Experimental Design, Implementation, and Policy
Considerations", RFC 1273, DOI 10.17487/RFC1273, November Considerations", RFC 1273, DOI 10.17487/RFC1273, November
1991, <https://www.rfc-editor.org/info/rfc1273>. 1991, <https://www.rfc-editor.org/info/rfc1273>.
[RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI
10.17487/RFC2474, December 1998, <http://www.rfc- 10.17487/RFC2474, December 1998, <http://www.rfc-
editor.org/info/rfc2474>. editor.org/info/rfc2474>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC
2914, DOI 10.17487/RFC2914, September 2000, <https://www
.rfc-editor.org/info/rfc2914>.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z. [RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z.
Shelby, "Performance Enhancing Proxies Intended to Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135, DOI Mitigate Link-Related Degradations", RFC 3135, DOI
10.17487/RFC3135, June 2001, <http://www.rfc-editor.org/ 10.17487/RFC3135, June 2001, <http://www.rfc-editor.org/
info/rfc3135>. info/rfc3135>.
[RFC3168] Ramakrishnan, K., Floyd, S. and D. Black, "The Addition of [RFC3168] Ramakrishnan, K., Floyd, S. and D. Black, "The Addition of
Explicit Congestion Notification (ECN) to IP", RFC 3168, Explicit Congestion Notification (ECN) to IP", RFC 3168,
DOI 10.17487/RFC3168, September 2001, <http://www.rfc- DOI 10.17487/RFC3168, September 2001, <http://www.rfc-
editor.org/info/rfc3168>. editor.org/info/rfc3168>.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and [RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002, Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002,
<http://www.rfc-editor.org/info/rfc3234>. <http://www.rfc-editor.org/info/rfc3234>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393, DOI
10.17487/RFC3393, November 2002, <https://www.rfc-
editor.org/info/rfc3393>.
[RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G. and M. [RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G. and M.
Sooriyabandara, "TCP Performance Implications of Network Sooriyabandara, "TCP Performance Implications of Network
Path Asymmetry", BCP 69, RFC 3449, DOI 10.17487/RFC3449, Path Asymmetry", BCP 69, RFC 3449, DOI 10.17487/RFC3449,
December 2002, <http://www.rfc-editor.org/info/rfc3449>. December 2002, <http://www.rfc-editor.org/info/rfc3449>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <http://www.rfc-editor.org/info/rfc3550>. July 2003, <http://www.rfc-editor.org/info/rfc3550>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J. and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004, <http://www
.rfc-editor.org/info/rfc3819>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>. December 2005, <http://www.rfc-editor.org/info/rfc4301>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI
10.17487/RFC4302, December 2005, <http://www.rfc- 10.17487/RFC4302, December 2005, <http://www.rfc-
editor.org/info/rfc4302>. editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, DOI 10.17487/RFC4303, December 2005, <http://www 4303, DOI 10.17487/RFC4303, December 2005, <http://www
skipping to change at page 31, line 5 skipping to change at page 32, line 53
[RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A. and R. [RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A. and R.
Whitner, "Improved Packet Reordering Metrics", RFC 5236, Whitner, "Improved Packet Reordering Metrics", RFC 5236,
DOI 10.17487/RFC5236, June 2008, <http://www.rfc- DOI 10.17487/RFC5236, June 2008, <http://www.rfc-
editor.org/info/rfc5236>. editor.org/info/rfc5236>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/ (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
RFC5246, August 2008, <http://www.rfc-editor.org/info/ RFC5246, August 2008, <http://www.rfc-editor.org/info/
rfc5246>. rfc5246>.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
March 2009, <https://www.rfc-editor.org/info/rfc5481>.
[RFC5559] Eardley, P., Ed., "Pre-Congestion Notification (PCN) [RFC5559] Eardley, P., Ed., "Pre-Congestion Notification (PCN)
Architecture", RFC 5559, DOI 10.17487/RFC5559, June 2009, Architecture", RFC 5559, DOI 10.17487/RFC5559, June 2009,
<http://www.rfc-editor.org/info/rfc5559>. <http://www.rfc-editor.org/info/rfc5559>.
[RFC5925] Touch, J., Mankin, A. and R. Bonica, "The TCP [RFC5925] Touch, J., Mankin, A. and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925, Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <http://www.rfc-editor.org/info/rfc5925>. June 2010, <http://www.rfc-editor.org/info/rfc5925>.
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P. and P. [RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P. and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, DOI Roberts, "Issues with IP Address Sharing", RFC 6269, DOI
skipping to change at page 31, line 54 skipping to change at page 33, line 54
197, RFC 7567, DOI 10.17487/RFC7567, July 2015, <http:// 197, RFC 7567, DOI 10.17487/RFC7567, July 2015, <http://
www.rfc-editor.org/info/rfc7567>. www.rfc-editor.org/info/rfc7567>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C. and D. Borkmann, Trammell, B., Huitema, C. and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A "Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624, DOI Threat Model and Problem Statement", RFC 7624, DOI
10.17487/RFC7624, August 2015, <http://www.rfc-editor.org/ 10.17487/RFC7624, August 2015, <http://www.rfc-editor.org/
info/rfc7624>. info/rfc7624>.
[RFC7713] Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)
Concepts, Abstract Mechanism, and Requirements", RFC 7713,
DOI 10.17487/RFC7713, December 2015, <http://www.rfc-
editor.org/info/rfc7713>.
[RFC7872] Gont, F., Linkova, J., Chown, T. and W. Liu, "Observations [RFC7872] Gont, F., Linkova, J., Chown, T. and W. Liu, "Observations
on the Dropping of Packets with IPv6 Extension Headers in on the Dropping of Packets with IPv6 Extension Headers in
the Real World", RFC 7872, DOI 10.17487/RFC7872, June the Real World", RFC 7872, DOI 10.17487/RFC7872, June
2016, <https://www.rfc-editor.org/info/rfc7872>. 2016, <https://www.rfc-editor.org/info/rfc7872>.
[RFC7928] Kuhn, N., Ed., Natarajan, P., Ed., Khademi, N.Ed., and D. [RFC7928] Kuhn, N., Ed., Natarajan, P., Ed., Khademi, N.Ed., and D.
Ros, "Characterization Guidelines for Active Queue Ros, "Characterization Guidelines for Active Queue
Management (AQM)", RFC 7928, DOI 10.17487/RFC7928, July Management (AQM)", RFC 7928, DOI 10.17487/RFC7928, July
2016, <http://www.rfc-editor.org/info/rfc7928>. 2016, <http://www.rfc-editor.org/info/rfc7928>.
skipping to change at page 33, line 11 skipping to change at page 35, line 5
Comments from the community are welcome on the text and Comments from the community are welcome on the text and
recommendations. recommendations.
-05 Corrections received and helpful inputs from Mohamed Boucadair. -05 Corrections received and helpful inputs from Mohamed Boucadair.
-06 Updated following comments from Stephen Farrell, and feedback via -06 Updated following comments from Stephen Farrell, and feedback via
email. Added a draft conclusion section to sketch some strawman email. Added a draft conclusion section to sketch some strawman
scenarios that could emerge. scenarios that could emerge.
-07 Updated following comments from Al Morton, Chris Seal, and other
feedback via email.
Authors' Addresses Authors' Addresses
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Department of Engineering Department of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen, AB24 3UE Aberdeen, AB24 3UE
Scotland Scotland
Email: gorry@erg.abdn.ac.uk Email: gorry@erg.abdn.ac.uk
 End of changes. 102 change blocks. 
488 lines changed or deleted 532 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/