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Versions: (draft-fairhurst-tsvwg-transport-encrypt)
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TSVWG G. Fairhurst
Internet-Draft University of Aberdeen
Intended status: Informational C. Perkins
Expires: May 29, 2019 University of Glasgow
November 25, 2018
The Impact of Transport Header Confidentiality on Network Operation and
Evolution of the Internet
draft-ietf-tsvwg-transport-encrypt-03
Abstract
This document describes implications of applying end-to-end
encryption at the transport layer. It identifies in-network uses of
transport layer header information. It then reviews the implications
of developing end-to-end transport protocols that use authentication
to protect the integrity of transport information or encryption to
provide confidentiality of the transport protocol header and expected
implications of transport protocol design and network operation.
Since transport measurement and analysis of the impact of network
characteristics have been important to the design of current
transport protocols, it also considers the impact on transport and
application evolution.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 29, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 3
3. Current uses of Transport Headers within the Network . . . . 10
3.1. Observing Transport Information in the Network . . . . . 10
3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 16
3.3. Use for Network Diagnostics and Troubleshooting . . . . . 19
3.4. Header Compression . . . . . . . . . . . . . . . . . . . 20
4. Encryption and Authentication of Transport Headers . . . . . 21
5. Addition of Transport Information to Network-Layer Protocol
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6. Implications of Protecting the Transport Headers . . . . . . 26
6.1. Independent Measurement . . . . . . . . . . . . . . . . . 26
6.2. Characterising "Unknown" Network Traffic . . . . . . . . 27
6.3. Accountability and Internet Transport Protocols . . . . . 27
6.4. Impact on Research, Development and Deployment . . . . . 28
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 29
8. Security Considerations . . . . . . . . . . . . . . . . . . . 31
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33
11. Informative References . . . . . . . . . . . . . . . . . . . 33
Appendix A. Revision information . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction
There is increased interest in, and deployment of, new protocols that
employ end-to-end encryption at the transport layer, including the
transport layer headers. An example of such a transport is the QUIC
transport protocol [I-D.ietf-quic-transport], currently being
standardised in the IETF. Encryption of transport layer headers and
payload data has many benefits in terms of protecting user privacy.
These benefits have been widely discussed [RFC7258], [RFC7624], and
this document strongly supports the increased use of encryption in
transport protocols. There are also, however, some costs, in that
the widespread use of transport encryption requires changes to
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network operations, and complicates network measurement for research,
operational, and standardisation purposes.
This document discusses some consequences of applying end-to-end
encryption at the transport layer. It reviews the implications of
developing end-to-end transport protocols that use encryption to
provide confidentiality of the transport protocol header, and
considers the effect of such changes on transport protocol design and
network operations. It also considers anticipated implications on
transport and application evolution.
Transports are increasingly encrypting and authenticating the payload
(i.e., the application data carried within the transport connection)
end-to-end. Such protection is encouraged, and iits implications are
not further discussed in this memo.
2. Context and Rationale
The transport layer provides end-to-end interactions between
endpoints (processes) using an Internet path. Transport protocols
layer directly over the network-layer service and are sent in the
payload of network-layer packets. They support end-to-end
communication between applications, supported by higher-layer
protocols, running on the end systems (or transport endpoints). This
simple architectural view hides one of the core functions of the
transport, however, to discover and adapt to the properties of the
Internet path that is currently being used. The design of Internet
transport protocols is as much about trying to avoid the unwanted
side effects of congestion on a flow and other capacity-sharing
flows, avoiding congestion collapse, adapting to changes in the path
characteristics, etc., as it is about end-to-end feature negotiation,
flow control and optimising for performance of a specific
application.
To achieve stable Internet operations the IETF transport community
has to date relied heavily on measurement and insights of the network
operations community to understand the trade-offs, and to inform
selection of appropriate mechanisms, to ensure a safe, reliable, and
robust Internet (e.g., [RFC1273]). In turn, the network operations
community relies on being able to understand the pattern and
requirements of traffic passing over the Internet, both in aggregate
and at the flow level.
There are many motivations for deploying encrypted transports
[RFC7624] (i.e., transport protocols that use encryption to provide
confidentiality of some or all of the transport-layer header
information), and encryption of transport payloads (i.e.
confidentiality of the payload data). The increasing public concerns
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about interference with Internet traffic have led to a rapidly
expanding deployment of encryption to protect end-user privacy, e.g.,
QUIC [I-D.ietf-quic-transport]. Encryption is also expected to form
a basis of future transport protocol designs.
Some network operators and access providers have come to rely on the
in-network measurement of transport properties and the functionality
provided by middleboxes to both support network operations and
enhance performance. There can therefore be implications when
working with encrypted transport protocols that hide transport header
information from the network. These present architectural challenges
and considerations in the way transport protocols are designed, and
ability to characterise and compare different transport solutions
[Measure]. Implementations of network devices are encouraged to
avoid side-effects when protocols are updated. Introducing
cryptographic integrity checks to header fields can also prevent
undetected manipulation of the field by network devices, or
undetected addition of information to a packet. However, this does
not prevent inspection of the information by a 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.
Reliance on the presence and semantics of specific header information
leads to ossification. An endpoint could be required to supply a
specific header to receive the network service that it desires. In
some cases, this could be benign or advantageous to the protocol
(e.g., recognising the start of a connection, or explicitly exposing
protocol information can be expected to provide more consistent
decisions by on-path devices than the use of diverse methods to infer
semantics from other flow properties); in other cases this is not
beneficial (e.g., a mechanism implemented in a network device, such
as a firewall, that required a header field to have only a specific
known set of values 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, preventing evolution of
the protocol).
Examples of the impact of ossification on transport protocol design
and ease of deployment can be seen in the case of Multipath TCP
(MPTCP) and the TCP Fast Open option. The design of MPTCP had to be
revised to account for middleboxes, so called "TCP Normalizers", that
monitor the evolution of the window advertised in the TCP headers and
that reset connections if the window does not grow as expected.
Similarly, TCP Fast Open has had issues with middleboxes that remove
unknown TCP options, that drop segments with unknown TCP options,
that drop segments that contain data and have the SYN bit set, that
drop packets with SYN/ACK that acknowledge data, or that disrupt
connections that send data before the three-way handshake completes.
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In both cases, the issue was caused by middleboxes that had a hard-
coded understanding of transport behaviour, and that interacted
poorly with transports that tried to change that behaviour. Other
examples have included middleboxes that rewrite TCP sequence and
acknowledgement numbers but are unaware of the (newer) SACK option
and don't correctly rewrite selective acknowledgements to match the
changes made to the fixed TCP header.
A protocol design that uses header encryption can provide
confidentiality of some or all of the protocol header information.
This prevents an on-path device from gaining knowledge of the header
field. It therefore prevents mechanisms being built that directly
rely on the information or seek to infer semantics of an exposed
header field. Using encryption to provide confidentiality of the
transport layer brings some well-known privacy and security benefits
and can therefore help reduce ossification of the transport layer.
In particular, it is important that protocols either do not expose
information where the usage could change in future protocols, or that
methods that utilise the information are robust to potential changes
as protocols evolve over time. To avoid unwanted inspection, a
protocol could also intentionally vary the format and/or value of
header fields (sometimes known as Greasing
[I-D.thomson-quic-grease]). However, while encryption hides the
protocol header information, it does not prevent ossification of the
network service. People seeking understanding of network traffic
could come to rely on pattern inferences and other heuristics as the
basis for network decision and to derive measurement data, creating
new dependencies on the transport protocol.
Specification of non-encrypted transport header fields explicitly
allows protocol designers to make specific header information
observable in the network. This supports other uses of this
information by on-path devices, and at the same time this can be
expected to lead to ossification of the transport header, because
network forwarding could evolve to depend on the presence and/or
value of these fields. The decision about which transport headers
fields are made observable offers trade-offs around authentication
and confidentiality versus observability, network operations and
management, and ossification. For example, a design that provides
confidentiality of protocol header information can impact the
following activities that rely on measurement and analysis of traffic
flows:
Network Operations and Research: Observable transport headers enable
both operators and the research community to measure and analyse
protocol performance, network anomalies, and failure pathologies.
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This information can help inform capacity planning, and assist in
determining the need for equipment and/or configuration changes by
network operators.
The data can also inform Internet engineering research, and help
in the development of new protocols, methodologies, and
procedures. Concealing the transport protocol header information
makes the stream performance unavailable to passive observers
along the path, and likely leads to the development of alternative
methods to collect or infer that data.
Providing confidentiality of the transport payload, but leaving
some, or all, of the transport headers unencrypted, possibly with
authentication, can provide the majority of the privacy and
security benefits while supporting operations and research, but at
the cost of ossifying the transport headers.
Protection from Denial of Service: Observable transport headers
currently provide useful input to classify traffic and detect
anomalous events (e.g., changes in application behaviour,
distributed denial of service attacks). To be effective, this
protection needs to be able to uniquely disambiguate unwanted
traffic. An inability to separate this traffic using packet
header information could result in less-efficient identification
of unwanted traffic or development of different methods (e.g.
rate-limiting of uncharacterised traffic).
Network Troubleshooting and Diagnostics: Encrypting transport
header information eliminates the incentive for operators to
troubleshoot since they cannot interpret the data. A flow
experiencing packet loss or jitter looks like an unaffected flow
when only observing network layer headers (if transport sequence
numbers and flow identifiers are obscured). This limits
understanding of the impact of packet loss or latency on the
flows, or even localizing the network segment causing the packet
loss or latency. Encrypted traffic could imply "don't touch" to
some, and could limit a trouble-shooting response to "can't help,
no trouble found". Additional mechanisms will need to be
introduced to help reconstruct or replace transport-level metrics
to support troubleshooting and diagnostics, but these add
complexity and operational costs (e.g., in deploying additional
functions in equipment or adding traffic overhead).
Network Traffic Analysis: Hiding transport protocol header
information can make it harder to determine which transport
protocols and features are being used across a network segment and
to measure trends in the pattern of usage. This could impact the
ability for an operator to anticipate the need for network
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upgrades and roll-out. It can also impact the on-going traffic
engineering activities performed by operators (such as determining
which parts of the path contribute delay, jitter or loss). While
the impact could, in many cases, be small there are scenarios
where operators directly support particular services (e.g., to
troubleshoot issues relating to Quality of Service, QoS; the
ability to perform fast re-routing of critical traffic, or support
to mitigate the characteristics of specific radio links). The
more complex the underlying infrastructure the more important this
impact.
Open and Verifiable Network Data: Hiding transport protocol header
information can reduce the range of actors that can capture useful
measurement data. This limits the information sources available
to the Internet 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.
The cooperating dependence of network, application, and host to
provide communication performance on the Internet is uncertain
when only endpoints (i.e., at user devices and within service
platforms) can observe performance, and when performance cannot be
independently verified by all parties. The ability of other
stakeholders to review transport header traces can help develop
deeper insight into performance. In the heterogeneous Internet,
this helps extend the range of topologies, vendor equipment, and
traffic patterns that are evaluated.
Independently captured data is important to help ensure the health
of the research and development communities. It can provide input
and test scenarios to support development of new transport
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 be
utilised to demonstrate regulatory compliance in some
jurisdictions, and to provide a basis for informing design
decisions.
The last point leads us to consider the impact of hiding transport
headers in the specification and development of protocols and
standards. This has potential impact on:
o Understanding Feature Interactions: An appropriate vantage point,
coupled with timing information about traffic flows, provides a
valuable tool for benchmarking equipment, functions, and/or
configurations, and to understand complex feature interactions.
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An inability to observe transport protocol information can limit
the ability to diagnose and explore interactions between features
at different protocol layers, a side-effect of not allowing a
choice of vantage point from which this information is observed.
o Supporting Common Specifications: Transmission Control Protocol
(TCP) is currently the predominant transport protocol used over
Internet paths. Its many variants have broadly consistent
approaches to avoiding congestion collapse, and to ensuring the
stability of the Internet. Increased use of transport layer
encryption can overcome ossification, allowing deployment of new
transports and different types of congestion control. This
flexibility can be beneficial, but it can come at the cost of
fragmenting the ecosystem. There is little doubt that developers
will try to produce high quality transports for their intended
target uses, but it is not clear there are sufficient incentives
to ensure good practice that benefits the wide diversity of
requirements for the Internet community as a whole. Increased
diversity, and the ability to innovate without public scrutiny,
risks point solutions that optimise for specific needs, but
accidentally disrupt operations of/in different parts of the
network. The social contract that maintains the stability of the
Internet relies on accepting common specifications.
o Operational Practice: The network operations community relies on
being able to understand the pattern and requirements of traffic
passing over the Internet, both in aggregate and at the flow
level. These operational practices have developed based on the
information available from unencrypted transport headers. If this
information is only carried in encrypted transport headers,
operators will not be able to use this information directly. If
operators still wish to use these practices, they may turn to more
ambitious ways of discovering this information. For example, if
an operator wants to know that traffic is audio traffic, and no
longer has access to Session Description Protocol (SDP) session
descriptions that would explicitly say a flow "is audio", the
operator might use heuristics to guess that short UDP packets with
regular spacing are carrying audio traffic. Operational practices
aimed at guessing transport parameters are out of scope for this
document, and are only mentioned here to recognize that encryption
may not prevent operators from attempting to apply the same
practices they used with unencrypted transport headers.
o Compliance: Published transport specifications allow operators and
regulators to check compliance. This can bring assurance to those
operating networks, often avoiding the need to deploy complex
techniques that routinely monitor and manage TCP/IP traffic flows
(e.g., avoiding the capital and operational costs of deploying
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flow rate-limiting and network circuit-breaker methods [RFC8084]).
When it is not possible to observe transport header information,
methods are still needed to confirm that the traffic produced
conforms to the expectations of the operator or developer.
o Restricting research and development: Hiding transport information
can impede independent research into new mechanisms, measurement
of behaviour, and development initiatives. Experience shows that
transport protocols are complicated to design and complex to
deploy, and that individual mechanisms need to be evaluated while
considering other mechanisms, across a broad range of network
topologies and with attention to the impact on traffic sharing the
capacity. If this results in reduced availability of open data,
it could eliminate the independent self-checks to the
standardisation process that have previously been in place from
research and academic contributors (e.g., the role of the IRTF
Internet Congestion Control Research Groups (ICCRG) and research
publications in reviewing new transport mechanisms and assessing
the impact of their experimental deployment)
In summary, there are trade-offs. On the one hand, transport
protocol designers have often ignored the implications of whether the
information in transport header fields can or will be used by in-
network devices, and the implications this places on protocol
evolution. This motivates a design that provides confidentiality of
the header information. On the other hand, it can be expected that a
lack of visibility of transport header information can impact the
ways that protocols are deployed, standardised, and their operational
support.
To achieve stable Internet operations the IETF transport community
has to date relied heavily on measurement and insights of the network
operations community to understand the trade-offs, and to inform
selection of appropriate mechanisms, to ensure a safe, reliable, and
robust Internet (e.g., [RFC1273],[RFC2914]).
The choice of whether future transport protocols encrypt their
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. As [RFC7258] notes:
"Making networks unmanageable to mitigate [pervasive monitoring] is
not an acceptable outcome, but ignoring [pervasive monitoring] would
go against the consensus documented here. An appropriate balance
will emerge over time as real instances of this tension are
considered." This balance between information exposed and
information concealed ought to be carefully considered when
specifying new transport protocols.
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3. Current uses of Transport Headers within the Network
Despite transport headers having end-to-end meaning, some of these
transport headers have come to be used in various ways within the
Internet. In response to pervasive monitoring [RFC7624] revelations
and the IETF consensus that "Pervasive Monitoring is an Attack"
[RFC7258], efforts are underway to increase encryption of Internet
traffic,. Applying confidentiality to transport header fields would
affect how protocol information is used [RFC8404]. To understand
these implications, it is first necessary to understand how transport
layer headers are currently observed and/or modified by middleboxes
within the network.
Transport protocols can be designed to encrypt or authenticate
transport header fields. Authentication at the transport layer can
be used to detect any changes to an immutable header field that were
made by a network device along a path. The intentional modification
of transport headers by middleboxes (such as Network Address
Translation, NAT, or Firewalls) is not considered. Common issues
concerning IP address sharing are described in [RFC6269].
3.1. Observing Transport Information in the Network
If in-network observation of transport protocol headers is needed,
this requires knowledge of the format of the transport header:
o Flows need to be identified at the level required to perform the
observation;
o The protocol and version of the header need to be visible, e.g.,
by defining the wire image [I-D.trammell-wire-image]. As
protocols evolve over time and there could be a need to introduce
new transport headers. This could require interpretation of
protocol version information or connection setup information;
o The location and syntax of any observed transport headers needs to
be known. IETF transport protocols can specify this information.
The following subsections describe various ways that observable
transport information has been utilised.
3.1.1. Flow Identification
Transport protocol header information (together with information in
the network header), has been used to identify a flow and the
connection state of the flow, together with the protocol options
being used. In some usages, a low-numbered (well-known) transport
port number has been used to identify a protocol (although port
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information alone is not sufficient to guarantee identification of a
protocol, since applications can use arbitrary ports, multiple
sessions can be multiplexed on a single port, and ports can be re-
used by subsequent sessions).
Transport protocols, such as TCP and the Stream Control Transport
Protocol (SCTP) specify a standard base header that includes sequence
number information and other data, with the possibility to negotiate
additional headers at connection setup, identified by an option
number in the transport header. UDP-based protocols can use, but
sometimes do not use, well-known port numbers. Some flows can
instead be identified by observing signalling protocol data (e.g.,
[RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of magic
numbers placed in the first byte(s) of the datagram payload
[RFC7983].
Flow identification is a common function. For example, performed by
measurement activities, QoS classification, firewalls, Denial of
Service, DOS, prevention. It becomes more complex and less easily
achieved when multiplexing is used at or above the transport layer.
3.1.2. Metrics derived from Transport Layer Headers
Some actors manage their portion of the Internet by characterizing
the performance of link/network segments. Passive monitoring uses
observed traffic to make inferences from transport headers to derive
these performance metrics. A variety of open source and commercial
tools have been deployed that utilise this information. The
following metrics can be derived from transport header information:
Traffic Rate and Volume: Header information (e.g., sequence number
and packet size) allows derivation of volume measures per-
application, to characterise the traffic that uses a network
segment or the pattern of network usage. This can be measured per
endpoint or for an aggregate of endpoints (e.g., by an operator to
assess subscriber usage). It can also be used to trigger
measurement-based traffic shaping and to implement QoS support
within the network and lower layers. Volume measures can be
valuable for capacity planning and providing detail of trends,
rather than the volume per subscriber.
Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g.,
from transport sequence numbers) and has been used as a metric for
performance assessment and to characterise transport behaviour.
Understanding the location and root cause of loss can help an
operator determine whether this requires corrective action.
Network operators have used the variation in patterns of loss as a
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key performance metric, utilising this to detect changes in the
offered service.
There are various causes of loss, including corruption of link
frames (e.g., interference on a radio link), buffer overflow
(e.g., due to congestion), policing (traffic management), buffer
management (e.g., Active Queue Management, AQM [RFC7567]), and
inadequate provision of traffic pre-emption. Understanding flow
loss rate requires either maintaining per flow packet counters or
by observing sequence numbers in transport headers. Loss can be
monitored at the interface level by devices in the network. It is
often valuable to understand the conditions under which packet
loss occurs. This usually requires relating loss to the traffic
flowing on the network node/segment at the time of loss.
Observation of transport feedback information (e.g., RTP Control
Protocol (RTCP) reception reports [RFC3550], TCP SACK blocks) can
increase understanding of the impact of loss and help identify
cases where loss could have been wrongly identified, or the
transport did not require the lost packet. It is sometimes more
helpful to understand the pattern of loss, than the loss rate,
because losses can often occur as bursts, rather than randomly-
timed events.
Throughput and Goodput: The throughput achieved by a flow can be
determined even when a flow is encrypted, providing the individual
flow can be identified. Goodput [RFC7928] is a measure of useful
data exchanged (the ratio of useful/total volume of traffic sent
by a flow). This requires ability to differentiate loss and
retransmission of packets (e.g., by observing packet sequence
numbers in the TCP or the Real-time Transport Protocol, RTP,
headers [RFC3550]).
Latency: Latency is a key performance metric that impacts
application response time and user-perceived response time. It
often indirectly impacts throughput and flow completion time.
Latency determines the reaction time of the transport protocol
itself, impacting flow setup, congestion control, loss recovery,
and other transport mechanisms. The observed latency can have
many components [Latency]. Of these, unnecessary/unwanted queuing
in network buffers has often been observed as a significant factor
[bufferbloat]. Once the cause of unwanted latency has been
identified, this can often be eliminated.
To measure latency across a part of a path, an observation point
can measure the experienced round trip time (RTT) using packet
sequence numbers, and acknowledgements, or by observing header
timestamp information. Such information allows an observation
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point in the network to determine not only the path RTT, but also
to measure the upstream and downstream contribution to the RTT.
This could be used to locate a source of latency, e.g., by
observing cases where the median RTT is much greater than the
minimum RTT for a part of a path.
The service offered by network operators can benefit from latency
information to understand the impact of deployment and tune
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]
[RFC8290] and although parameter-less methods are desired
[RFC7567], current methods [RFC8290] [RFC8289] [RFC8033] often
cannot scale across all possible deployment scenarios.
Variation in delay: Some network applications are sensitive to small
changes in packet timing. To assess the performance of such
applications, it can be necessary to measure the variation in
delay observed along a portion of the path [RFC3393] [RFC5481].
The requirements resemble those for the measurement of latency.
Flow Reordering: Significant packet reordering within a flow can
impact time-critical applications and can be interpreted as loss
by reliable transports. Many transport protocol techniques are
impacted by reordering (e.g., triggering TCP retransmission, or
re-buffering of real-time applications). Packet reordering can
occur for many reasons, from equipment design to misconfiguration
of forwarding rules. Since this impacts transport performance,
network tools are needed to detect and measure unwanted/excessive
reordering.
There have been initiatives in the IETF transport area to reduce
the impact of reordering within a transport flow, possibly leading
to a reduction in the requirements for preserving ordering. These
have promise to simplify network equipment design as well as the
potential to improve robustness of the transport service.
Measurements of reordering can help understand the present level
of reordering within deployed infrastructure, and inform decisions
about how to progress such mechanisms. Key performance indicators
are retransmission rate, packet drop rate, sector utilisation
level, a measure of reordering, peak rate, the ECN congestion
experienced (CE) marking rate, etc.
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Metrics have been defined that evaluate whether a network has
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 needed to
understand the context under which the data was collected,
including the time, observation point, and way in which metrics
were accumulated. The RTCP protocol directly reports some of this
information in a form that can be directly visible in the network.
A user of summary measurement data needs to trust the source of
this data and the method used to generate the summary information.
The above passively monitor transport protocol headers to derive
metrics about network layer performance useful for operation and
management of a network.
3.1.3. Transport use of Network Layer Header Fields
Information from the transport protocol can be used by a multi-field
classifier as a part of policy framework. Policies are commonly used
for management of the QoS or Quality of Experience (QoE) in resource-
constrained networks and by firewalls that use the information to
implement access rules (see also section 2.2.2 of [RFC8404]).
Network-layer classification methods that rely on a multi-field
classifier (e.g. Inferring QoS from the 5-tuple or choice of
application protocol) are incompatible with transport protocols that
encrypt the transport information. Traffic that cannot be
classified, will typically receive a default treatment.
Transport information can also be explicitly set in network-layer
header fields that are not encrypted. This can provide information
to enable a different forwarding treatment by the network, even when
a transport employs encryption to protect other header information.
On the one hand, the user of a transport that multiplexes multiple
sub-flows could wish to hide the presence and characteristics of
these sub-flows. On the other hand, an encrypted transport could set
the network-layer information to indicate the presence of sub-flows
and to reflect the network needs of individual sub-flows. There are
several ways this could be done:
Using the IPv6 Network-Layer Flow Label: Endpoints are encouraged to
set the IPv6 Flow Label field of the network-layer header (e.g.,
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[RFC8085]). The label can provide information that can help
inform network-layer queuing, forwarding (e.g., for Equal Cost
Multi-Path, ECMP, routing, and Link Aggregation, LAG) [RFC6294].
A multiplexing transport could choose to use multiple flow labels
to allow the network to independently forward subflows.
Using the Network-Layer Differentiated Services Code Point:
Applications can expose their delivery expectations to the network
by setting the Differentiated Services Code Point (DSCP) field of
IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications
identify different forwarding treatments for individual sub-flows
(audio vs. video) based on the value of the DSCP field
[I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information
to inform network-layer queuing and forwarding, rather than an
operator inferring traffic requirements from transport and
application headers via a multi-field classifier.
Since the DSCP value can impact the quality of experience for a
flow., observations of service performance need to consider this
field when a network path has support for differentiated service
treatment.
Using Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that utilises the ECN field in the network-layer header.
Use of ECN explicitly informs the network-layer that a transport
is ECN-capable, and requests ECN treatment of the flows packets.
An ECN-capable transport can offer benefits when used over a path
with equipment that implements an AQM method with Congestion
Experienced (CE) marking of IP packets [RFC8087], since it can
react to congestion without also having to recover from lost
packets.
ECN exposes the presence of congestion. The reception of CE-
marked packets can be used to estimate the level of incipient
congestion on the upstream portion of the path from the point of
observation (Section 2.5 of [RFC8087]). Interpreting the marking
behaviour (i.e., assessing congestion and diagnosing faults)
requires context from the transport layer (such as path RTT).
AQM and ECN offer a range of algorithms and configuration options.
Tools therefore need to be available to network operators and
researchers to understand the implication of configuration choices
and transport behaviour as use of ECN increases and new methods
emerge [RFC7567].
Careful use of the network layer features can therefore help address
some of the reasons why the network inspects transport protocol
headers.
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3.2. Transport Measurement
The common language between network operators and application/content
providers/users is packet transfer performance at a layer that all
can view and analyse. For most packets, this has been the transport
layer, until the emergence of QUIC, with the obvious exception of
Virtual Private Networks (VPNs) and IPsec.
When encryption conceals more layers in each packet, people seeking
understanding of the network operation rely more on pattern
inferences and other heuristics reliance on pattern inferences and
accuracy suffers. For example, the traffic patterns between server
and browser are dependent on browser supplier and version, even when
the sessions use the same server application (e.g., web e-mail
access). It remains to be seen whether more complex inferences can
be mastered to produce the same monitoring accuracy (see section
2.1.1 of [RFC8404]).
When measurement datasets are made available by servers or client
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
involved in observing packets on high rate links. This exports only
the packet header information of (randomly) selected packets. The
utility of these measurements depends on the type of bearer and
number of mechanisms used by network devices. Simple routers are
relatively easy to manage, a device with more complexity demands
understanding of the choice of many system parameters. This level of
complexity exists when several network methods are combined.
This section discusses topics concerning observation of transport
flows, with a focus on transport measurement.
3.2.1. Point of Observation
On-path measurements are particularly useful for locating the source
of problems, or to assess the performance of a network segment or a
particular device configuration. Often issues can only be understood
in the context of the other flows that share a particular path,
common network device, interface port, etc. A simple example is
monitoring of a network device that uses a scheduler or active queue
management technique [RFC7567], where it could be desirable to
understand whether the algorithms are correctly controlling latency,
or if overload protection is working. This understanding implies
knowledge of how traffic is assigned to any sub-queues used for flow
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scheduling, but can also require information about how the traffic
dynamics impact active queue management, starvation prevention
mechanisms, and circuit-breakers.
Sometimes multiple on-path observation points are needed. By
correlating observations of headers at multiple points along the path
(e.g., at the ingress and egress of a network segment), an observer
can determine the contribution of a portion of the path to an
observed metric, to locate a source of delay, jitter, loss,
reordering, congestion marking, etc.
3.2.2. Use by Operators to Plan and Provision Networks
Traffic measurements (e.g., traffic volume, loss, latency) is used by
operators to help plan deployment of new equipment and configurations
in their networks. Data is also valuable to equipment vendors who
want to understand traffic trends and patterns of usage as inputs to
decisions about planning products and provisioning for new
deployments. This measurement information can also be correlated
with billing information when this is also collected by an operator.
A network operator supporting traffic that uses transport header
encryption might not have access to per-flow measurement data.
Trends in aggregate traffic can be observed and can be related to the
endpoint addresses being used, but it may be impossible to correlate
patterns in measurements with changes in transport protocols (e.g.,
the impact of changes in introducing a new transport protocol
mechanism). This increases the dependency on other indirect sources
of information to inform planning and provisioning.
3.2.3. Service Performance Measurement
Traffic measurements (e.g., traffic volume, loss, latency) can be
used by various actors to help analyse the performance offered to the
users of a network segment, and to inform operational practice.
While active measurements may be used within a network, passive
measurements can have advantages in terms of eliminating unproductive
test traffic, reducing the influence of test traffic on the overall
traffic mix, and the ability to choose the point of observation (see
Section 3.2.1). However, passive measurements can rely on observing
transport headers which is not possible if those headers are
encrypted.
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3.2.4. Measuring Transport to Support Network Operations
Information provided by tools observing transport headers can help
determine whether mechanisms are needed in the network to prevent
flows from acquiring excessive network capacity. Operators can
implement operational practices to manage traffic flows (e.g., to
prevent flows from acquiring excessive network capacity under severe
congestion) by deploying rate-limiters, traffic shaping or network
transport circuit breakers [RFC8084].
Congestion Control Compliance of Traffic: Congestion control is a
key transport function [RFC2914]. Many network operators
implicitly accept that TCP traffic complies with a behaviour that
is acceptable for use in the shared Internet. TCP algorithms have
been continuously improved over decades, and they have reached a
level of efficiency and correctness that custom application-layer
mechanisms will struggle to easily duplicate [RFC8085].
A standards-compliant TCP stack provides congestion control that
may therefore be judged safe for use across the Internet.
Applications developed on top of well-designed transports can be
expected to appropriately control their network usage, reacting
when the network experiences congestion, by back-off and reduce
the load placed on the network. This is the normal expected
behaviour for IETF-specified transport (e.g., TCP and SCTP).
However, when anomalies are detected, tools can interpret the
transport protocol header information to help understand the
impact of specific transport protocols (or protocol mechanisms) on
the other traffic that shares a network. An observation in the
network can gain understanding of the dynamics of a flow and its
congestion control behaviour. Analysing observed flows can help
to build confidence that an application flow backs-off its share
of the network load in the face of persistent congestion, and
hence to understand whether the behaviour is appropriate for
sharing limited network capacity. For example, it is common to
visualise plots of TCP sequence numbers versus time for a flow to
understand how a flow shares available capacity, deduce its
dynamics in response to congestion, etc. The ability to identify
sources that contribute excessive congestion is important to safe
operation of network infrastructure, and mechanisms can inform
configuration of network devices to complement the endpoint
congestion avoidance mechanisms [RFC7567] [RFC8084] to avoid a
portion of the network being driven into congestion collapse
[RFC2914].
Congestion Control Compliance for UDP traffic: UDP provides a
minimal message-passing datagram transport that has no inherent
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congestion control mechanisms. Because congestion control is
critical to the stable operation of the Internet, applications and
other protocols that choose to use UDP as a transport are required
to employ mechanisms to prevent congestion collapse, avoid
unacceptable contributions to jitter/latency, and to establish an
acceptable share of capacity with concurrent traffic [RFC8085].
A network operator needs tools to understand if datagram flows
comply with congestion control expectations and therefore whether
there is a need to deploy methods such as rate-limiters, transport
circuit breakers or other methods to enforce acceptable usage for
the offered service.
UDP flows that expose a well-known header by specifying the format
of header fields can allow information to be observed to gain
understanding of the dynamics of a flow and its congestion control
behaviour. For example, tools exist to monitor various aspects of
the RTP and RTCP header information of real-time flows (see
Section 3.1.2, and the Secure RTP extensions [RFC3711] were
explicitly designed to expose header information to enable such
observation.
3.3. Use for Network Diagnostics and Troubleshooting
Transport header information can be useful for a variety of
operational tasks [RFC8404]: to diagnose network problems, assess
network provider performance, evaluate equipment/protocol
performance, capacity planning, management of security threats
(including denial of service), and responding to user performance
questions. Sections 3.1.2 and 5 of [RFC8404] provide further
examples. These tasks seldom involve the need to determine the
contents of the transport payload, or other application details.
A network operator supporting traffic that uses transport header
encryption can see only encrypted transport headers. This prevents
deployment of performance measurement tools that rely on transport
protocol information. Choosing to encrypt all the information
reduces the ability of an operator to observe transport performance,
and could limit the ability of network operators to trace problems,
make appropriate QoS decisions, or response to other queries about
the network service. For some this will be blessing, for others it
may be a curse. For example, operational performance data about
encrypted flows needs to be determined by traffic pattern analysis,
rather than relying on traditional tools. This can impact the
ability of the operator to respond to faults, it could require
reliance on endpoint diagnostic tools or user involvement in
diagnosing and troubleshooting unusual use cases or non-trivial
problems. A key need here is for tools to provide useful information
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during network anomalies (e.g., significant reordering, high or
intermittent loss). Many network operators currently utilise
observed transport information as a part of their operational
practice. However, the network will not break just because transport
headers are encrypted, although alternative diagnostic and
troubleshooting tools would need to be developed and deployed.
Measurements can be used to monitor the health of a portion of the
Internet, to provide early warning of the need to take action. They
can assist in debugging and diagnosing the root causes of faults that
concern a particular user's traffic. They can also be used to
support post-mortem investigation after an anomaly to determine the
root cause of a problem.
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 capacity 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
network segment. An alternative approach is to use in-network
techniques that observe transport packet headers in operational
networks to make the measurements.
In other cases, measurement involves dissecting network traffic
flows. The observed transport layer information can help identify
whether the link/network tuning is effective and alert to potential
problems that can be hard to derive from link or device measurements
alone. The design trade-offs for radio networks are often very
different to those of wired networks. A radio-based network (e.g.,
cellular mobile, enterprise WiFi, satellite access/back-haul, point-
to-point radio) has the complexity of a subsystem that performs radio
resource management,s with direct impact on the available capacity,
and potentially loss/reordering of packets. The impact of the
pattern of loss and congestion, differs for different traffic types,
correlation with propagation and interference can all have
significant impact on the cost and performance of a provided service.
The need for this type of information is expected to increase as
operators bring together heterogeneous types of network equipment and
seek to deploy opportunistic methods to access radio spectrum.
3.4. Header Compression
Header compression saves link bandwidth by compressing network and
transport protocol headers on a per-hop basis. It was widely used
with low bandwidth dial-up access links, and still finds application
on wireless links that are subject to capacity constraints. Header
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compression has been specified for use with TCP/IP and RTP/UDP/IP
flows [RFC2507], [RFC2508], [RFC4995].
While it is possible to compress only the network layer headers,
significant bandwidth savings can be made if both the network and
transport layer headers are compressed together as a single unit.
The Secure RTP extensions [RFC3711] were explicitly designed to leave
the transport protocol headers unencrypted, but authenticated, since
support for header compression was considered important. Encrypting
the transport protocol headers does not break such header
compression, but does cause it to fall back to compressing only the
network layer headers, with a significant reduction in efficiency.
This may have operational impact.
4. Encryption and Authentication of Transport Headers
End-to-end encryption can be applied at various protocol layers. It
can be applied above the transport to encrypt the transport payload.
Encryption methods can hide information from an eavesdropper in the
network. Encryption can also help protect the privacy of a user, by
hiding data relating to user/device identity or location. Neither an
integrity check nor encryption methods prevent traffic analysis, and
usage needs to reflect that profiling of users, identification of
location and fingerprinting of behaviour can take place even on
encrypted traffic flows. Any header information that has a clear
definition in the protocol's message format(s), or is implied by that
definition, and is not cryptographically confidentiality-protected
can be unambiguously interpreted by on-path observers
[I-D.trammell-wire-image].
There are several motivations:
o One motive to use encryption is a response to perceptions that the
network has become ossified by over-reliance on middleboxes that
prevent new protocols and mechanisms from being deployed. This
has lead to a 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].
o Another motivation stems from increased concerns about privacy and
surveillance. Some Internet users have valued the ability to
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protect identity, user location, and defend against traffic
analysis, and have used methods such as IPsec Encapsulated
Security Payload (ESP), Virtual Private Networks (VPNs) and other
encrypted tunnel technologies. 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 could include
some form of transport header encryption (e.g., QUIC
[I-D.ietf-quic-transport]).
Authentication methods (that provide integrity checks of protocols
fields) have also been specified at the network layer, and this also
protects transport header fields. The network layer itself carries
protocol header fields that are increasingly used to help forwarding
decisions reflect the need of transport protocols, such as the IPv6
Flow Label [RFC6437], DSCP, and ECN fields.
The use of transport layer authentication and encryption exposes a
tussle between middlebox vendors, operators, applications developers
and users.
o On the one hand, future Internet protocols that enable large-scale
encryption assist in the restoration of the end-to-end nature of
the Internet by returning complex processing to the endpoints,
since middleboxes cannot modify what they cannot see.
o On the other hand, encryption of transport layer header
information has implications for people who are responsible for
operating networks and researchers and analysts seeking to
understand the dynamics of protocols and traffic patterns.
Whatever the motives, a decision to use pervasive transport header
encryption will have implications on the way in which design and
evaluation is performed, and which can in turn impact the direction
of evolution of the transport protocol stack. While the IETF can
specify protocols, the success in actual deployment is often
determined by many factors [RFC5218] that are not always clear at the
time when protocols are being defined.
The following briefly reviews some security design options for
transport protocols. A Survey of Transport Security Protocols
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[I-D.ietf-taps-transport-security] provides more details concerning
commonly used encryption methods at the transport layer.
Authenticating the Transport Protocol Header: Transport layer header
information can be authenticated. An integrity check that
protects the immutable transport header fields, but can still
expose the transport protocol header information in the clear,
allowing in-network devices to observe these fields. An integrity
check can not prevent in-network modification, but can prevent a
receiving from accepting changes and avoid impact on the transport
protocol operation.
An example transport authentication mechanism is TCP-
Authentication (TCP-AO) [RFC5925]. This TCP option authenticates
the IP pseudo header, TCP header, and TCP data. TCP-AO protects
the transport layer, preventing attacks from disabling the TCP
connection itself and provides replay protection. TCP-AO may
interact with middleboxes, depending on their behaviour [RFC3234].
The IPsec Authentication Header (AH) [RFC4302] was designed to
work at the network layer and authenticate the IP payload. This
approach authenticates all transport headers, and verifies their
integrity at the receiver, preventing in-network modification.
Secure RTP [RFC3711] is another example of a transport protocol
that allows header authentication.
Greasing: Transport layer header information that is observable can
be observed in the network. Protocols often provide extensibility
features, reserving fields or values for use by future versions of
a specification. The specification of receivers has traditionally
ignored unspecified values, however in-network devices have
emerged that ossify to require a certain value in a field, or re-
use a field for another purpose. When the specification is later
updated, it is impossible to deploy the new use of the field, and
forwarding of the protocol could even become conditional on a
specific header field value.
A protocol can intentionally vary the value, format, and/or
presence of observable transport header fields. This behaviour,
known as GREASE (Generate Random Extensions And Sustain
Extensibility), is designed to avoid a network device ossifying
the use of a specific observable field. Greasing seeks to ease
deployment of new methods. It can be designed to prevent in-
network devices utilising the information in a transport header,
or can make an observation robust to a set of changing values,
rather than a specific set of values.
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Encrypting the Transport Payload: The transport layer payload can be
encrypted to protect the content of transport segments. This
leaves transport protocol header information in the clear. The
integrity of immutable transport header fields could be protected
by combining this with an integrity check.
Examples of encrypting the payload include Transport Layer
Security (TLS) over TCP [RFC8446] [RFC7525], Datagram TLS (DTLS)
over UDP [RFC6347] [RFC7525], Secure RTP [RFC3711], and TCPcrypt
[I-D.ietf-tcpinc-tcpcrypt] which permits opportunistic encryption
of the TCP transport payload.
Encrypting the Transport Headers and Payload: The network layer
payload could be encrypted (including the entire transport header
and the payload). This method provides confidentiality of the
entire transport packet. It therefore does not expose any
transport information to devices in the network, which also
prevents modification along a network path.
One example of encryption at the network layer is use of IPsec
Encapsulating Security Payload (ESP) [RFC4303] in tunnel mode.
This encrypts and authenticates all transport headers, preventing
visibility of the transport headers by in-network devices. Some
Virtual Private Network (VPN) methods also encrypt these headers.
Selectively Encrypting Transport Headers and Payload: A transport
protocol design can encrypt selected header fields, while also
choosing to authenticate the entire transport header. This allows
specific transport header fields to be made observable by network
devices. End-to end integrity checks can prevent an endpoint from
undetected modification of the immutable transport headers.
Mutable fields in the transport header provide opportunities for
middleboxes to modify the transport behaviour (e.g., the extended
headers described in [I-D.trammell-plus-abstract-mech]). This
considers only immutable fields in the transport headers, that is,
fields that can be authenticated End-to-End across a path.
An example of a method that encrypts some, but not all, transport
information is GRE-in-UDP [RFC8086] when used with GRE encryption.
Optional Encryption of Header Information: There are implications to
the use of optional header encryption in the design of a transport
protocol, where support of optional mechanisms can increase the
complexity of the protocol and its implementation and in the
management decisions that are required to use variable format
fields. Instead, fields of a specific type ought to always be
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sent with the same level of confidentiality or integrity
protection.
As seen, different transports use encryption to protect their header
information to varying degrees. There is, however, a trend towards
increased protection with newer transport protocols.
5. Addition of Transport Information to Network-Layer Protocol Headers
Transport protocol information can be made visible in a network-layer
header. This has the advantage that this information can then be
observed by in-network devices.
Information from the transport protocol can be used by a multi-field
classifier to prioritise flows as a part of a policy framework. This
was discussed in Section 3.1.3.
Some measurements can be made by adding additional protocol headers
carrying operations, administration and management (OAM) information
to packets at the ingress to a maintenance domain (e.g., an Ethernet
protocol header with timestamps and sequence number information using
a method such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data])
and removing the additional header at the egress of the maintenance
domain. This approach enables some types of measurements, but does
not cover the entire range of measurements described in this
document. In some cases, it can be difficult to position measurement
tools at the required segments/nodes and there can be challenges in
correlating the downsream/upstream information when in-band OAM data
is inserted by an on-path device. This has the advantage that a
single header can support all transport protocols, but there could
also be less desirable implications of separating the operation of
the transport protocol from the measurement framework.
Another example of a network-layer approach is the IPv6 Performance
and Diagnostic Metrics (PDM) Destination Option [RFC8250]. This
allows a sender to optionally include a destination option that
caries header fields that can be used to observe timestamps and
packet sequence numbers. This information could be authenticated by
receiving transport endpoints when the information is added at the
sender and visible at the receiving endpoint, although methods to do
this have not currently been proposed. This method needs to be
explicitly enabled at the sender.
Current measurements suggest it can be undesirable to rely on methods
requiring the presence of network options or extension headers. IPv4
network options are often not supported (or are carried on a slower
processing path) and some IPv6 networks are also known to drop
packets that set an IPv6 header extension (e.g., [RFC7872]). Another
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disadvantage is that protocols that separately expose header
information do not necessarily have an advantage to expose the
information that is utilised by the protocol itself, and could
manipulate this header information to gain an advantage from the
network.
6. 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
transport protocols.
6.1. Independent Measurement
Independent observation by multiple actors is important for
scientific analysis. Encrypting transport header encryption changes
the ability for other actors to collect and independently analyse
data. Internet transport protocols employ a set of mechanisms. Some
of these need to work in cooperation with the network layer - loss
detection and recovery, congestion detection and congestion control,
some of these need to work only end-to-end (e.g., parameter
negotiation, flow-control).
When encryption conceals information in the transport header, it
could be possible for an applications to provide summary data on
performance and usage of the network. This data could be made
available to other actors. However, this data needs to contain
sufficient detail to understand (and possibly reconstruct the network
traffic pattern for further testing) and to be correlated with the
configuration of the network paths being measured.
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
transport protocol in their header information (e.g., timestamps used
to calculate the RTT, packet numbers used to asses congestion and
requests for retransmission) provide an incentive for the sending
endpoint to provide correct information, increasing confidence that
the observer understands the transport interaction with the network.
This can support decisions when considering changes to transport
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protocols, changes in network infrastructure, or the emergence of new
traffic patterns.
6.2. Characterising "Unknown" Network Traffic
The patterns and types of traffic that share Internet capacity change
over time as networked applications, usage patterns and protocols
continue to evolve.
If "unknown" or "uncharacterised" traffic patterns form a small part
of the traffic aggregate passing through a network device or segment
of the network the path, the dynamics of the uncharacterised traffic
may not have a significant collateral impact on the performance of
other traffic that shares this network segment. Once the proportion
of this traffic increases, the need to monitor the traffic and
determine if appropriate safety measures need to be put in place.
Tracking the impact of new mechanisms and protocols requires traffic
volume to be measured and new transport behaviours to be identified.
This is especially true of protocols operating over a UDP substrate.
The level and style of encryption needs to be considered in
determining how this activity is performed. On a shorter timescale,
information may also need to be collected to manage denial of service
attacks against the infrastructure.
6.3. Accountability and Internet Transport Protocols
Information provided by tools observing transport headers can be used
to classify traffic, and to limit the network capacity used by
certain flows. Operators can potentially use this information to
prioritise or de-prioritise certain flows or classes of flow, with
potential implications for network neutrality, or to rate limit
malicious or otherwise undesirable flows (e.g., for Distributed
Denial of Service, DDOS, protection, or to ensure compliance with a
traffic profile, as discussed in Section 3.2.4). Equally, operators
could use analysis of transport headers and transport flow state to
demonstrate that they are not providing differential treatment to
certain flows. Obfuscating or hiding this information using
encryption may lead operators and maintainers of middleboxes
(firewalls, etc.) to seek other methods to classify, and potentially
other mechanisms to condition, network traffic.
A lack of data reduces the level of precision with which flows can be
classified and conditioning mechanisms can be applied (e.g., rate
limiting, circuit breaker techniques [RFC8084], or blocking of
uncharacterised traffic), and this needs to be considered when
evaluating the impact of designs for transport encryption [RFC5218].
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6.4. Impact on Research, Development and Deployment
The majority of present Internet applications use two well-known
transport protocols, TCP and UDP. Although TCP represents the
majority of current traffic, some 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.
Looking ahead, there will be a need to update these protocols and to
develop and deploy new transport mechanisms and protocols. There are
both opportunities and also challenges to the design, evaluation and
deployment of new transport protocol mechanisms.
Integrity checks can protect an endpoint from undetected modification
of protocol fields by network devices, whereas encryption and
obfuscation can further prevent these headers from 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
critical role in the design of transport protocol mechanisms and
their acceptance by the wider community (e.g., as a method to judge
the safety for Internet deployment). Observation of pathologies are
also important in understanding the interactions between cooperating
protocols and network mechanism, the implications of sharing capacity
with other traffic and the impact of different patterns of usage.
Evolution and the ability to understand (measure) the impact need to
proceed hand-in-hand. Attention needs to be paid to the expected
scale of deployment of new protocols and protocol mechanisms.
Whatever the mechanism, experience has shown that it is often
difficult to correctly implement combination of mechanisms [RFC8085].
These mechanisms therefore typically evolve as a protocol matures, or
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
increased pace of transport evolution, and with it the possibility to
experiment with and deploy a wide range of protocol mechanisms.
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There has been recent interest in a wide range of new transport
methods, e.g., Larger Initial Window, Proportional Rate Reduction
(PRR), congestion control methods based on measuring bottleneck
bandwidth and round-trip propagation time, the introduction of AQM
techniques and new forms of ECN response (e.g., Data Centre TCP,
DCTP, and methods proposed for L4S).The growth and diversity of
applications and protocols using the Internet also continues to
expand. For each new method or application it is desirable to build
a body of data reflecting its behaviour under a wide range of
deployment scenarios, traffic load, and interactions with other
deployed/candidate methods.
Open standards motivate a desire for this evaluation to include
independent observation and evaluation of performance data, which in
turn suggests control over where and when measurement samples are
collected. This requires consideration of the appropriate balance
between encrypting all and no transport information.
7. Conclusions
Confidentiality and strong integrity checks have properties that are
being incorporated into new protocols and that have important
benefits. The pace of development of transports using the WebRTC
data channel and the rapid deployment of QUIC transport protocol can
both be attributed to using the combination of UDP as a substrate
while providing confidentiality and authentication of the
encapsulated transport headers and payload.
The traffic that can be observed by on-path network devices is a
function of transport protocol design/options, network use,
applications, and user characteristics. In general, when only a
small proportion of the traffic has a specific (different)
characteristic, such traffic seldom leads to operational concern,
although the ability to measure and monitor it is less. The desire
to understand the traffic and protocol interactions typically grows
as the proportion of traffic increases in volume. The challenges
increase when multiple instances of an evolving protocol contribute
to the traffic that share network capacity.
An increased pace of evolution therefore needs to be accompanied by
methods that can be successfully deployed and used across operational
networks. This leads to a need for network operators (at various
level (ISPs, enterprises, firewall maintainer, etc) to identify
appropriate operational support functions and procedures.
Protocols that change their transport header format (wire format) or
their behaviour (e.g., algorithms that are needed to classify and
characterise the protocol), will require new tooling to be developed
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to catch-up with the changes. If the currently deployed tools and
methods are no longer relevant then it may no longer be posisble to
correctly measure performance. This can increase the response-time
after faults, and can impact the ability to manage the network
resulting in traffic causing traffic to be treated inappropriately
(e.g., rate limiting because of being incorrectly classified/
monitored).
There are benefits in exposing consistent information to the network
that avoids traffic being mis-classified and then receiving a default
treatment by the network. The flow label and DSCP fields provide
examples of how transport information can be made available for
network-layer decisions. Extension headers could also be used to
carry transport information that can inform network-layer decisions.
As a part of its design a new protocol specification therefore needs
to weigh the benefits of ossifying common headers, versus the
potential demerits of exposing specific information that could be
observed along the network path, to provide tools to manage new
variants of protocols. This can be done for the entire transport
header, or by dividing header fields between those that are
observable and mutable; those that are observable, but imutable; and
those that are hidden/obfusticated.
Several scenarios to illustrate different ways this could evolve are
provided below:
o One scenario is when transport protocols provide consistent
information to the network by intentionally exposing a part of the
transport header. The design fixes the format of this information
between versions of the protocol. This ossification of the
transport header allows an operator to establish tooling and
procedures that enable it to provide consistent traffic management
as the protocol evolves. In contrast to TCP (where all protocol
information is exposed), evolution of the transport is facilitated
by providing cryptographic integrity checks of the transport
header fields (preventing undetected middlebox changes) and
encryption of other protocol information (preventing observation
within the network, or incentivising the use of the exposed
information, rather than inferring information from other
characteristics of the flow traffic). The exposed transport
information can be used by operators to provide troubleshooting,
measurement and any necessary functions appropriate to the class
of traffic (priority, retransmission, reordering, circuit
breakers, etc).
o An alternative scenario adopts different design goals, with a
different outcome. A protocol that encrypts all header
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information forces network operators to act independently from
apps/transport developments to extract the information they need
to manage their network. A range of approaches could proliferate,
as in current networks. Some operators can add a shim header to
each packet as a flow as it crosses the network; other operators/
managers could develop heuristics and pattern recognition to
derive information that classifies flows and estimates quality
metrics for the service being used; some could decide to rate-
limit or block traffic until new tooling is in place. In many
cases, the derived information can be used by operators to provide
necessary functions appropriate to the class of traffic (priority,
retransmission, reordering, circuit breakers, etc).
Troubleshooting, and measurement becomes more difficult, and more
diverse. This could require additional information beyond that
visible in the packet header and when this information is used to
inform decisions by on-path devices it can lead to dependency on
other characteristics of the flow. In some cases, operators might
need access to keying information to interpret encrypted data that
they observe. Some use cases could demand use of transports that
do not use encryption.
The direction in which this evolves could have significant
implications on the way the Internet architecture develops. It
exposes a risk that significant actors (e.g., developers and
transport designers) achieve more control of the way in which the
Internet architecture develops.In particular, there is a possibility
that designs could evolve to significantly benefit of customers for a
specific vendor, and that communities with very different network,
applications or platforms could then suffer at the expense of
benefits to their vendors own customer base. In such a scenario,
there could be no incentive to support other applications/products or
to work in other networks leading to reduced access for new
approaches.
8. Security Considerations
This document is about design and deployment considerations for
transport protocols. Issues relating to security are discussed in
the various sections of the document.
Authentication, confidentiality protection, and integrity protection
are identified as Transport Features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a
protocol or layer on top of the transport protocol
[I-D.ietf-taps-transport-security].
Confidentiality and strong integrity checks have properties that can
also be incorporated into the deisgn of a transport protocol.
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Integrity checks can protect an endpoint from undetected modification
of protocol fields by network devices, whereas encryption and
obfuscation or greasing 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. A protocol specification needs to weigh the benefits
of ossifying common headers, versus the potential demerits of
exposing specific information that could be observed along the
network path to provide tools to manage new variants of protocols.
A protocol design that uses header encryption can provide
confidentiality of some or all of the protocol header information.
This prevents an on-path device from knowledge of the header field.
It therefore prevents mechanisms being built that directly rely on
the information or seeks to infer semantics of an exposed header
field. Hiding headers can limit the ability to measure and
characterise traffic.
Exposed transport headers are sometimes utilised as a part of the
information to detect anomalies in network traffic. This can be used
as the first line of defence yo identify potential threats from DOS
or malware and redirect suspect traffic to dedicated nodes
responsible for DOS analysis, malware detection, or to perform packet
"scrubbing" (the normalization of packets so that there are no
ambiguities in interpretation by the ultimate destination of the
packet). These techniques are currently used by some operators to
also defend from distributed DOS attacks.
Exposed transport header fields are sometimes also utilised as a part
of the information used by the receiver of a transport protocol to
protect the transport layer from data injection by an attacker. In
evaluating this use of exposed header information, it is important to
consider whether it introduces a significant DOS threat. For
example, an attacker could construct a DOS attack by sending packets
with a sequence number that falls within the currently accepted range
of sequence numbers at the receiving endpoint, this would then
introduce additional work at the receiving endpoint, even though the
data in the attacking packet may not finally be delivered by the
transport layer. This is sometimes known as a "shadowing attack".
An attack can, for example, disrupt receiver processing, trigger loss
and retransmission, or make a receiving endpoint perform unproductive
decryption of packets that cannot be successfully decrypted (forcing
a receiver to commit decryption resources, or to update and then
restore protocol state).
One mitigation to off-path attack is to deny knowledge of what header
information is accepted by a receiver or obfusticate the accepted
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header information, e.g., setting a non-predictable initial value for
a sequence number during a protocol handshake, as in [RFC3550] and
[RFC6056], or a port value that can not be predicted (see section 5.1
of [RFC8085]). A receiver could also require additional information
to be used as a part of check before accepting packets at the
transport layer (e.g., utilising a part of the sequence number space
that is encrypted; or by verifying an encrypted token not visible to
an attacker). This would also mitigate on-path attacks. An
additional processing cost can be incurred when decryption needs to
be attempted before a receiver is able to discard injected packets.
Open standards motivate a desire for this evaluation to include
independent observation and evaluation of performance data, which in
turn suggests control over where and when measurement samples are
collected. This requires consideration of the appropriate balance
between encrypting all and no transport information. Open data, and
accessibility to tools that can help understand trends in application
deployment, network traffic and usage patterns can all contribute to
understanding security challenges.
9. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX
This memo includes no request to IANA.
10. Acknowledgements
The authors would like to thank Mohamed Boucadair, Spencer Dawkins,
Tom Herbert, Jana Iyengar, Mirja Kuehlewind, Kyle Rose, Kathleen
Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, and other
members of the TSVWG for their comments and feedback.
This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No 688421.The
opinions expressed and arguments employed reflect only the authors'
view. The European Commission is not responsible for any use that
may be made of that information.
This work has received funding from the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1.
11. Informative References
[bufferbloat]
Gettys, J. and K. Nichols, "Bufferbloat: dark buffers in
the Internet. Communications of the ACM, 55(1):57-65",
January 2012.
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[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
"Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
data-03 (work in progress), June 2018.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-14 (work
in progress), August 2018.
[I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-19
(work in progress), November 2017.
[I-D.ietf-taps-transport-security]
Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey
of Transport Security Protocols", draft-ietf-taps-
transport-security-02 (work in progress), June 2018.
[I-D.ietf-tcpinc-tcpcrypt]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic protection of TCP Streams
(tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-12 (work in
progress), June 2018.
[I-D.ietf-tsvwg-l4s-arch]
Briscoe, B., Schepper, K., and M. Bagnulo, "Low Latency,
Low Loss, Scalable Throughput (L4S) Internet Service:
Architecture", draft-ietf-tsvwg-l4s-arch-02 (work in
progress), March 2018.
[I-D.ietf-tsvwg-rtcweb-qos]
Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP
Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb-
qos-18 (work in progress), August 2016.
[I-D.thomson-quic-grease]
Thomson, M., "More Apparent Randomization for QUIC",
draft-thomson-quic-grease-00 (work in progress), December
2017.
[I-D.trammell-plus-abstract-mech]
Trammell, B., "Abstract Mechanisms for a Cooperative Path
Layer under Endpoint Control", draft-trammell-plus-
abstract-mech-00 (work in progress), September 2016.
Fairhurst & Perkins Expires May 29, 2019 [Page 34]
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[I-D.trammell-wire-image]
Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", draft-trammell-wire-image-04 (work in
progress), April 2018.
[Latency] Briscoe, B., "Reducing Internet Latency: A Survey of
Techniques and Their Merits, IEEE Comm. Surveys &
Tutorials. 26;18(3) p2149-2196", November 2014.
[Measure] Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement-
based Protocol Design, Eur. Conf. on Networks and
Communications, Oulu, Finland.", June 2017.
[RFC1273] Schwartz, M., "Measurement Study of Changes in Service-
Level Reachability in the Global TCP/IP Internet: Goals,
Experimental Design, Implementation, and Policy
Considerations", RFC 1273, DOI 10.17487/RFC1273, November
1991, <https://www.rfc-editor.org/info/rfc1273>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2507] Degermark, M., Nordgren, B., and S. Pink, "IP Header
Compression", RFC 2507, DOI 10.17487/RFC2507, February
1999, <https://www.rfc-editor.org/info/rfc2507>.
[RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
Headers for Low-Speed Serial Links", RFC 2508,
DOI 10.17487/RFC2508, February 1999,
<https://www.rfc-editor.org/info/rfc2508>.
[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.
Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135,
DOI 10.17487/RFC3135, June 2001,
<https://www.rfc-editor.org/info/rfc3135>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
Fairhurst & Perkins Expires May 29, 2019 [Page 35]
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[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002,
<https://www.rfc-editor.org/info/rfc3234>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[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>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/info/rfc4585>.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
DOI 10.17487/RFC4737, November 2006,
<https://www.rfc-editor.org/info/rfc4737>.
[RFC4995] Jonsson, L-E., Pelletier, G., and K. Sandlund, "The RObust
Header Compression (ROHC) Framework", RFC 4995,
DOI 10.17487/RFC4995, July 2007,
<https://www.rfc-editor.org/info/rfc4995>.
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[RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful
Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,
<https://www.rfc-editor.org/info/rfc5218>.
[RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A., and R.
Whitner, "Improved Packet Reordering Metrics", RFC 5236,
DOI 10.17487/RFC5236, June 2008,
<https://www.rfc-editor.org/info/rfc5236>.
[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>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056,
DOI 10.17487/RFC6056, January 2011,
<https://www.rfc-editor.org/info/rfc6056>.
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
P. Roberts, "Issues with IP Address Sharing", RFC 6269,
DOI 10.17487/RFC6269, June 2011,
<https://www.rfc-editor.org/info/rfc6269>.
[RFC6294] Hu, Q. and B. Carpenter, "Survey of Proposed Use Cases for
the IPv6 Flow Label", RFC 6294, DOI 10.17487/RFC6294, June
2011, <https://www.rfc-editor.org/info/rfc6294>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
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[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF
Recommendations Regarding Active Queue Management",
BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,
<https://www.rfc-editor.org/info/rfc7567>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015,
<https://www.rfc-editor.org/info/rfc7624>.
[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.
[RFC7928] Kuhn, N., Ed., Natarajan, P., Ed., Khademi, N., Ed., and
D. Ros, "Characterization Guidelines for Active Queue
Management (AQM)", RFC 7928, DOI 10.17487/RFC7928, July
2016, <https://www.rfc-editor.org/info/rfc7928>.
[RFC7983] Petit-Huguenin, M. and G. Salgueiro, "Multiplexing Scheme
Updates for Secure Real-time Transport Protocol (SRTP)
Extension for Datagram Transport Layer Security (DTLS)",
RFC 7983, DOI 10.17487/RFC7983, September 2016,
<https://www.rfc-editor.org/info/rfc7983>.
[RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White,
"Proportional Integral Controller Enhanced (PIE): A
Lightweight Control Scheme to Address the Bufferbloat
Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017,
<https://www.rfc-editor.org/info/rfc8033>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers",
BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
<https://www.rfc-editor.org/info/rfc8084>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
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[RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE-
in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086,
March 2017, <https://www.rfc-editor.org/info/rfc8086>.
[RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using
Explicit Congestion Notification (ECN)", RFC 8087,
DOI 10.17487/RFC8087, March 2017,
<https://www.rfc-editor.org/info/rfc8087>.
[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Mechanisms", RFC 8095,
DOI 10.17487/RFC8095, March 2017,
<https://www.rfc-editor.org/info/rfc8095>.
[RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6
Performance and Diagnostic Metrics (PDM) Destination
Option", RFC 8250, DOI 10.17487/RFC8250, September 2017,
<https://www.rfc-editor.org/info/rfc8250>.
[RFC8289] Nichols, K., Jacobson, V., McGregor, A., Ed., and J.
Iyengar, Ed., "Controlled Delay Active Queue Management",
RFC 8289, DOI 10.17487/RFC8289, January 2018,
<https://www.rfc-editor.org/info/rfc8289>.
[RFC8290] Hoeiland-Joergensen, T., McKenney, P., Taht, D., Gettys,
J., and E. Dumazet, "The Flow Queue CoDel Packet Scheduler
and Active Queue Management Algorithm", RFC 8290,
DOI 10.17487/RFC8290, January 2018,
<https://www.rfc-editor.org/info/rfc8290>.
[RFC8404] Moriarty, K., Ed. and A. Morton, Ed., "Effects of
Pervasive Encryption on Operators", RFC 8404,
DOI 10.17487/RFC8404, July 2018,
<https://www.rfc-editor.org/info/rfc8404>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
Fairhurst & Perkins Expires May 29, 2019 [Page 39]
Internet-Draft Transport Encryption November 2018
Appendix A. Revision information
-00 This is an individual draft for the IETF community.
-01 This draft was a result of walking away from the text for a few
days and then reorganising the content.
-02 This draft fixes textual errors.
-03 This draft follows feedback from people reading this draft.
-04 This adds an additional contributor and includes significant
reworking to ready this for review by the wider IETF community Colin
Perkins joined the author list.
Comments from the community are welcome on the text and
recommendations.
-05 Corrections received and helpful inputs from Mohamed Boucadair.
-06 Updated following comments from Stephen Farrell, and feedback via
email. Added a draft conclusion section to sketch some strawman
scenarios that could emerge.
-07 Updated following comments from Al Morton, Chris Seal, and other
feedback via email.
-08 Updated to address comments sent to the TSVWG mailing list by
Kathleen Moriarty (on 08/05/2018 and 17/05/2018), Joe Touch on
11/05/2018, and Spencer Dawkins.
-09 Updated security considerations.
-10 Updated references, split the Introduction, and added a paragraph
giving some examples of why ossification has been an issue.
-01 This resolved some reference issues. Updated section on
observation by devices on the path.
-02 Comments received from Kyle Rose, Spencer Dawkins and Tom
Herbert. The network-layer information has also been re-organised
after comments at IETF-103.
-03 Added a section on header compression and rewriting of sections
refering to RTP transport. This version contains author editorial
work and removed duplicate section.
Fairhurst & Perkins Expires May 29, 2019 [Page 40]
Internet-Draft Transport Encryption November 2018
Authors' Addresses
Godred Fairhurst
University of Aberdeen
Department of Engineering
Fraser Noble Building
Aberdeen AB24 3UE
Scotland
EMail: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/
Colin Perkins
University of Glasgow
School of Computing Science
Glasgow G12 8QQ
Scotland
EMail: csp@csperkins.org
URI: https://csperkins.org//
Fairhurst & Perkins Expires May 29, 2019 [Page 41]
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