TSVWG G. Fairhurst
Internet-Draft University of Aberdeen
Intended status: Informational C.S. Perkins
Expires: March 29, 2018 University of Glasgow
September 27, 2017
The Impact of Transport Header Encryption on Operation and Evolution of
the Internet
draft-fairhurst-tsvwg-transport-encrypt-04
Abstract
This document describes implications of applying end-to-end
encryption at the transport layer. It identifies some in-network
uses of transport layer header information that can be used with a
transport header integrity check. It reviews the implication of
developing encrypted end-to-end transport protocols and examines the
implication of developing and deploying encrypted end-to-end
transport protocols. Since transport measurement and analysis of the
impact of network characteristics have been important to the design
of current transport protocols, it also considers some anticipated
implications on transport and application evolution.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 29, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Current uses of Transport Headers within the Network . . . 6
1.1.1. Observing Transport Information in the Network . . . . 7
1.1.1.1. Flow Identification . . . . . . . . . . . . . . . 7
1.1.1.2. Metrics derived from Transport Layer Headers . . . 7
1.1.1.3. Metrics derived from Network Layer Headers . . . . 10
1.1.2. Transport Measurement . . . . . . . . . . . . . . . . 12
1.1.2.1. Point of Measurement . . . . . . . . . . . . . . . 12
1.1.2.2. Use by Operators to Plan and Provision Networks . 13
1.1.2.3. Service Performance Measurement . . . . . . . . . 13
1.1.2.4. Measuring Transport to Support Network Operations 13
1.1.3. Use for Network Diagnostics and Troubleshooting . . . 15
1.1.4. Observing Headers to Implement Network Policy . . . . 15
2. Encryption and Authentication of Transport Headers . . . . . . 15
2.1. Authenticating the Transport Protocol Header . . . . . . . 17
2.2. Encrypting the Transport Payload . . . . . . . . . . . . . 17
2.3. Encrypting the Transport Header . . . . . . . . . . . . . 18
2.4. Authenticating Transport Information and Selectively
Encrypting the Transport Header . . . . . . . . . . . . . 18
2.5. Adding Transport Information to Network-Layer Protocol
Headers . . . . . . . . . . . . . . . . . . . . . . . . . 18
3. Implications of Protecting the Transport Headers . . . . . . . 19
3.1. Independent Measurement . . . . . . . . . . . . . . . . . 19
3.2. Characterising "Unknown" Network Traffic . . . . . . . . . 20
3.3. Accountability and Internet Transport Protocols . . . . . 20
3.4. Impact on Research, Development and Deployment . . . . . . 21
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
5. Security Considerations . . . . . . . . . . . . . . . . . . . 22
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1. Normative References . . . . . . . . . . . . . . . . . . . 22
7.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. Revision information . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
This document discusses the implications of end-to-end encryption
applied at the transport layer, and examines the impact on transport
protocol design, usage, and network operations and management. It
also considers anticipated implications on transport and application
evolution.
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The transport layer provides the first end-to-end interactions across
the Internet. 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
endpoint). 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 select appropriate mechanisms, to ensure a safe,
reliable and robust Internet. In turn, the network operations
community relies on being able to understand the traffic passing over
the Internet, both in aggregate and at the flow level -- inspecting
transport layer headers to help understand traffic dynamics.
There are many motivations for deploying encrypted transports, and
encryption of transport payloads. The increasing public concerns
about the interference with Internet traffic have led to a rapidly
expanding deployment of encryption to protect end-user privacy, in
protocols like QUIC. At the same time, network operators and access
providers, especially in mobile networks, 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.
This document considers some implications of working with encrypted
transport protocols, and discusses trade-offs around authentication,
encryption of transport protocol headers. It describes some of the
architectural challenges and considerations in the way transport
protocols are designed when using encryption [Measure].
Encryption of the transport layer brings some well-known privacy and
security benefits, but also introduces various costs that need to be
considered. Specifically, it can impact the following activities
that rely on measurement and analysis of traffic flows:
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o Network Operations and Research: Observable transport headers
enable operators and the research community to measure and analyse
protocol performance, network anomalies, and failure pathologies.
This information can help inform capacity planning, and assist in
determining the need for equipment and/or configuration changes by
network operators. This data also can inform Internet engineering
research, and help the develop of new protocols and procedures.
Encryption of the entire transport protocol, including header
information, will restrict the availability of data, and might
lead to the development of alternative, and potentially more
intrusive, methods to acquire the needed data. Encrypting the
transport payload, but leaving some, or all, of the transport
headers unencrypted but authenticated can provide the majority of
the privacy and security benefits while allowing some measurement.
o Network Troubleshooting and diagnostics: Encrypting transport
header information eliminates the incentive for operators to
troubleshoot what they cannot interpret. A flow experiencing
packet loss 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 on the flows that share a network segment.
Encrypted traffic therefore implies "don't touch", and a likely
trouble-shooting response will be "can't help, no trouble found".
The additional mechanisms that will need to be introduced to help
reconstruct transport-level metrics add complexity and operational
costs [I-D.mm-wg-effect-encrypt].
o Network Traffic Analysis: The use of encryption can make it harder
to determine which transport protocols and features are being used
across a network segment. The trends in usage. This could impact
the ability for an operator to anticipate the need for network
upgrades and roll-out. It can also impact the on-going traffic
engineering activities performed by operators. While the impact
may, in many cases, be small there are scenarios where operators
directly support particular services (e.g., in radio links, or to
troubleshoot issues realting to Quality of Service, QoS). The more
complex the underlying infrastructure the more important this
impact.
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o Open and Verifiable Network Data: The use of transport header
encryption reduces the range of actors that can capture useful
measurement data. This is, of course, its goal. Doing so,
however, limits the information sources available to the Internet
community to understand the operation of transport protocols, so
preventing access to the information necessary to inform design
decisions and standards for new protocols and related operational
practices. There are dangers in a model where only endpoints
(i.e., at user devices and within service platforms) can observe
performance, and this cannot be independently verified. To ensure
the health of the standards and research communities, we need
independently captured data to develop on the behaviour of the
transports. Independently verifiable performance metrics might
also important in order to demonstrate regulatory compliance in
some jurisdictions.
The last point leads us to consider the impact of encrypting all the
transport headers the specification and development of protocols and
standards. It 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 and/or configurations,
and to understand complex feature interactions. Transport header
encryption limits 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: The Transmission Control Protocl
(TCP) is the predominant transport protocol. Its many variants
have broadly consistent approaches to avoiding congestion
collapse, and to ensuring the stability of the network. Increased
use of transport layer encryption can overcome ossification,
allowing deployment of new transports with different types of
congestion control. This flexibility can be beneficial, but it
comes at the cost of fragmenting the ecosystem. There's little
doubt that developers will try to produce high quality transports
for their 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 compact that maintains the stability of the
network relies on accepting common specifications, and on the
ability to verify that others also conform.
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o Operational practice: Published transport specifications allow
operators 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
flow rate-limiting and network circuit-breaker methods). This
should continue when encrypted transport headers are used, but
methods need to confirm that the traffic produced conforms to the
expectations of the operator or developer.
o Restricting research and development: The use of encryption may
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 mechanism, across a broad range of network
topologies and with attention to the impact on traffic sharing the
capacity. Adopting pervasive encryption of transport information
could eliminate the independent self-checks that have previously
been in place from research and academic contributors (e.g., the
role of the IRTF ICCRG, and research publications in reviewing new
transport mechanisms and assessing the impact of their
experimental deployment).
Pervasive use of transport header encryption can impact the ways that
protocols are designed, standardised, deployed, and operated. 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. A network that is secure but
unusable due to persistent congestion collapse is not an improvement,
and while that would be an extreme outcome proposals that impose high
costs for very limited benefits need to be considered carefully, to
ensure the benefits outweigh the costs.
1.1. Current uses of Transport Headers within the Network
The transport layer is the first end-to-end layer in the network
stack. Despite headers having end-to-end meaning, some 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, which would
prevent visibility of transport headers. This affects on how network
protocols are designed and used [I-D.mm-wg-effect-encrypt]. 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.
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Transport protocols can be designed to encrypt or authenticate
transport header fields. Authentication methods at the transport
layer can be sued 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 with Protocol Translation, NAT-PT, or Firewalls)
is not considered.
1.1.1. Observing Transport Information in the Network
In-network observation of transport protocol headers requires
knowledge of the format of the transport header:
o Flows need to be identified at the level required for monitoring;
o The protocol and version of the header need to be observable. As
protocols evolve over time and there may be a need to introduce
new transport headers. This may require interpretation of
protocol version information or connection setup information;
o Location and syntax of any transport headers to be observed. IETF
transport protocols specify this information.
The following subsections describe various ways that observable
transport information may be utilised.
1.1.1.1. Flow Identification
Transport protocol header information can 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 ) port can
identify a protocol (although port information alone is not
sufficient to guarantee identification of a protocol). Transport
protocols, such as TCP and 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 ports. Some can instead be
identified by signalling protocols or through the use of magic
numbers placed in the first byte(s) of the datagram payload.
1.1.1.2. Metrics derived from Transport Layer Headers
Some actors have a need to characterise the performance of link/
network segments. Passive monitoring uses observed traffic to makes
inferences from transport headers to derive these measurements. 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:
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Traffic Rate and Volume: Header infromation may allow derivation of
volume measures per-application, to characterise the traffic that
uses a network segment or the pattern of network usage. This may
be measured per endpoint or aggregate of endpoint (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 (providing detail of trends
rather than the volume per subscriber).
Loss Rate and Loss Pattern: Flow loss rate may be derived and is
often used as a metric for performance assessment and to
characterise transport behaviour. Understanding the root cause of
loss can help an operator determine whether this requires
corrective action.
There are various cause of loss, including: corruption on a link
(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). 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 important to understand the conditions under which packet
loss occurs. This usually requires relating loss to the traffic
flowing on the network segment at the time of loss.
Observation of transport feedback information (observing loss
reports, e.g., RTP Control Protocol (RTCP), TCP SACK) can increase
understanding of the impact of loss and help identify cases where
loss may have been wrongly identified, or the transport did not
require the lost packet. It is sometimes more important to
understand the pattern of loss, than the loss rate - since losses
can often occur as bursts, rather than randomly-timed events.
Throughput and Goodput: The throughput observed 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), which requires ability to differentiate loss and
retransmission of packets (e.g., by observing packet sequence
numbers in the TCP or the Real Time Protocol, RTP, headers
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[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.
Once the cause of unwanted latency has been identified, this can
often be eliminated, and determining latency metrics is a key
driver in the deployment of AQM [RFC7567], DiffServ [RFC2474], and
Explicit Congestion Notification (ECN) [RFC3168] [RFC8087].
To measure latency across a part of the 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
point in the network to determine not only the path RTT, but also
to measure the upstream and downstream contribution to the RTT.
This may be used to locate a source of latency, e.g., by observing
cases where the ratio of median to minimum RTT is large for a part
of a path.
An example usage of this method could identify excessive buffers
to help deploy or configure AQM [RFC7567] [RFC7928] to effectively
eliminate unnecessary queuing in routers and other devices. AQM
methods need to be deployed at the capacity bottleneck, but are
often deployed in combination with other techniques, such as
scheduling [RFC7567] [I-D.ietf-aqm-fq-codel] and although
parameter-less methods are desired [RFC7567], current methods [I-D
.ietf-aqm-fq-codel] [I-D.ietf-aqm-codel] [I-D.ietf-aqm-pie] often
cannot scale across all possible deployment scenarios. The
service offered by operators can therefore benefit from latency
information to understand the impact of deployment and tune
deployed services.
Jitter: Some network applications are sensitive to changes in packet
timing. For such applications, it can be necessary to measure the
jitter observed along a portion of the path. The requirements to
measure jitter resemble those for the measurement of latency.
Flow Reordering: Significant flow reordering 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
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of real-time applications). Packet reordering can occur for many
reasons (from equipment design to misconfiguration of forwarding
rules).
As in the drive to reduce network latency, there is a need for
operational tools to detect mis-ordered packet flows and quantify
the degree or reordering. Techniques for measuring reordering
typically observe packet sequence numbers. Metrics have been
defined that evaluate whether a network has maintained packet
order on a packet-by-packet basis [RFC4737] and [RFC5236].
There has been initiatives in the IETF transport area to reduce
the impact of reordering within a transport flow, possibly leading
to reduced the requirements for 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 level of reordering within
deployed infrastructure, and inform decisions about how to
progress such mechanisms.
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. Key
performance indicators are retransmission rate, packet drop rate,
sector utilization level, a measure of reordering, peak rate, the CE-
marking rate, etc. Metadata is often important 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.
When encryption conceals information in packet headers, measurements
need to rely on pattern inferences and other heuristics grows, and
accuracy suffers [I-D.mm-wg-effect-encrypt].
1.1.1.3. Metrics derived from Network Layer Headers
Some transport information is made visible in the network-layer
protocol header. These header fields are not encrypted and can be
used to make flow observations.
Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged expose
flow information in the IPv6 Flow Label field of the network-layer
header (e..g. [RFC8085]). This can be used to inform network-
layer queuing, forwarding (e.g., for equal cost multi-path (ECMP)
routing, and Link Aggregation, LAG). This can provide useful
information to assign packets to flows in the data collected by
measurement campaigns. Although important to characterising a
path, it does not directly provide any performance data.
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Use Network-Layer Differentiated Services Code Point Point: Applicati
on can expose their delivery expectations to the network by
setting the Differentiated Services Code Point (DSCP) field of
IPv4 and IPv6 packets. This can be used to inform network-layer
queuing and forwarding, and can also provide information on the
relative importance of packet information collected by measurement
campaigns, but does not directly provide any performance data.
This field provides explicit information that can be used in place
of inferring traffic requirements (e.g., by inferring QoS
requirements from port information via a multi-field classifier).
The DSCP value can therefore 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.
Use of Explicit Congestion Marking: ECN[RFC3168] is an optional
transport mechanism that uses a code point in the network-layer
header. Use of ECN can offer gains in terms of increased
throughput, reduced delay, and other benefits when used over a
path that includes equipment that supports an AQM method that
performs Congestion Experienced (CE) marking of IP packets
[RFC8087].
ECN exposes the presence of congestion on a network path to the
transport and network layer. The reception of CE-marked packets
can therefore be used to monitor the presence and estimate the
level of incipient congestion on the upstream portion of the path
from the point of observation (Section 2.5 of [RFC8087]). Because
ECN marks carried in the IP protocol header, it is much easier to
measure ECN than metering packet loss. However, interpreting the
marking behaviour (i.e., assessing congestion and diagnosing
faults) requires context from the transport layer (path RTT,
visibility of loss - that could be due to queue overflow,
congestion response, etc) [RFC7567].
Some ECN-capable network devices can provide richer (more frequent
and fine-grained) indication of their congestion state. Setting
congestion marks proportional to the level of congestion (e.g.,
Data Center TCP, DCTP [I-D.ietf-tcpm-dctcp], and Low Latency Low
Loss Scalable throughput, L4S, [I-D.ietf-tsvwg-l4s-arch].
Use of ECN requires feedback a transport to feed back reception
information on the path towards the data sender. Exposure of this
Transport ECN feedback provides an additional powerful tool to
understand ECN-enabled AQM-based networks [RFC8087].
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AQM and ECN offer a range of algorithms and configuration options,
it is therefore important for tools 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] [RFC8087]. ECN-
monitoring is expected to become important as AQM is deployed that
supports ECN [RFC8087].
1.1.2. 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 transport
layer, until the emergence of QUIC, with the obvious exception of
VPNs and IPsec. When encryption conceals more layers in a packet,
people seeking understanding of the network operation need to rely
more on pattern inferences and other heuristics. The accuracy of
measurements therefore suffers, as does the ability to investigate
and troubleshoot interactions between different anomalies. For
example, the traffic patterns between a web server and a browser are
dependent on browser supplier and version, even use of the
application (e.g., web e-mail access). Even when measurement datasets
are made available (e.g., from endpoints) additional metadata, such
as the state of the network, is often required to interpret the 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.
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1.1.2.1. Point of Measurement
Often measurements can only be understood in the context of the other
flows that share a bottleneck. A simple example is monitoring of
AQM. For example, FQ-CODEL [I-D.ietf-aqm-fq-codel], combines sub
queues (statistically assigned per flow), management of the queue
length (CODEL), flow-scheduling, and a starvation prevention
mechanism. Usually such algorithms are designed to be self-tuning,
but current methods typically employ heuristics that can result in
more loss under certain path conditions (e.g., large RTT, effects of
multiple bottlenecks [RFC7567]).
In-network measurements can distinguish between upstream and
downstream metrics with respect to the measurement point. These are
particularly useful for locating the source of problems or to assess
the performance of a network segment or a particular device
configuration.
By correlating observations 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.).
1.1.2.2. 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 important to equipment vendors who
need to understand traffic trends traffic 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 may not have access to per-flow measurement data. Trends
in aggregate traffic can be observed and can be related this to the
endpoint addresses being used, but it may not be possible 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.
1.1.2.3. Service Performance Measurement
Traffic measurements (e.g., traffic volume, loss, latency) can be
used by various actors to help analyse the performance available to
users of a network segment, and inform operational practice. While
active measurements may be used in-network passive measurements can
have advantages in terms of eliminating unproductive traffic,
reducing the influence of test traffic on the overall traffic mix,
and the ability to choose the point of measurement Section 1.1.2.1.
1.1.2.4. Measuring Transport to Support Network Operations
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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. Many network operators implicitly accept that
TCP traffic to comply 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 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 TCP and SCTP.
However when anomolies 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 packet sequence
numbers can be used to help 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.
Congestion Control Compliance for UDP Traffic UDP provides a minimal
message-passing transport that has no inherent 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 an Internet 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 UDP flows comply
with congestion control expectations and therefore whether there
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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 1.1.1.2.
1.1.3. Use for Network Diagnostics and Troubleshooting
Transport header information is useful for a variety of operational
tasks [I-D.mm-wg-effect-encrypt]: to diagnose network problems,
assess performance, capacity planning, management of denial of
service threats, and responding to user performance questions. 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 information may be
expected to reduce the ability for networks to "help" (e.g., in
response to tracing issues, making appropriate Quality of Service,
QoS, decisions). 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 that tools need to provide useful information during
network anomalies (e.g., significant reordering, high or intermittent
loss). Although many network operators utilise transport information
as a part of their operational practice, the network will not break
because transport headers are encrypted.
1.1.4. Observing Headers to Implement Network Policy
Information from the transport protocol can be used by a multi-field
classifier as a part of policy framework. Policies are commonly used
for QoS management for resource-constrained networks and by firewalls
that use the information to implement access rules. Traffic that
cannot be classified, will typically receive a default treatment.
2. Encryption and Authentication of Transport Headers
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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.
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 common perception that there is too much "manipulation" of
protocol headers within the network, and that designing to deploy in
such networks is preventing transport evolution. In the light of
this, a method that authenticates transport headers may help improve
the pace of transport development, by eliminating the need to always
consider deployed middleboxes [I-D.trammell-plus-abstract-mech], or
potentially to only explicitly enable middlebox use for particular
paths with particular middleboxes that are deliberately deployed to
realise a useful function for the network and/or users[RFC3135].
Another motivation stems from increased concerns about privacy and
surveillance. Some Internet users have valued the ability to protect
identity, user location, and defend against traffic analysis, and
have used methods such as IPsec ESP and Tor [Tor]. 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. Whatever the reasons, there
are now activities in the IETF to design new protocols that may
include some form of transport header encryption (e.g., QUIC [I-D
.ietf-quic-transport]).
Authentication methods (that provide integrity checks of protocols
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 the IPv6 Flow
Label [RFC6437], the Differentiated Services Code Point (DSCP)
[RFC2474] and Explicit Congestion Notification (ECN) [RFC3168].
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.
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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 of 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 TCP/IP stack.
The next subsections briefly review some security design options for
transport protocols.
2.1. 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 observes these fields. An
integrity check can not prevent in-network modification, but can
avoid a receiving 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 TCP segments,
including the IP pseudo header, TCP header, and TCP data. TCP-AO
protects the transport layer, preventing attacks from disabling the
TCP connection itself. TCP-AO may interact with middleboxes,
depending on their behaviour [RFC3234].
The IPsec Authentication Header (AH) [RFC4302] works at the network
layer and authenticates the IP payload. This therefore also
authenticates all transport headers, and verifies their integrity at
the receiver, preventing in-network modification.
2.2. 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
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header fields could be protected by combining this with an integrity
check (Section 2.1).
Examples of encrypting the payload include Transport Layer Security
(TLS) over TCP [RFC5246] [RFC7525] or Datagram TLS (DTLS) over UDP
[RFC6347] [RFC7525].
2.3. Encrypting the Transport Header
The network layer payload could be encrypted (including the entire
transport header and payload). This method does not expose any
transport information to devices in the network, which also prevents
modification along the network path.
The IPsec Encapsulating Security Payload (ESP) [RFC4303] is an
example of encryption at the network layer, it encrypts and
authenticates all transport headers, preventing visibility of the
headers by in-network devices. Some Virtual Private Network (VPN)
methods also encrypt these headers.
2.4. Authenticating Transport Information and Selectively Encrypting
the Transport Header
A transport protocol design can encrypt selected header fields, while
also choosing to authenticate fields in the 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.
The choice of which fields to expose and which to encrypt is a design
choice for the transport protocol. Any selective encryption method
requires trading two conflicting goals for a transport protocol
designer to decide which header fields to encrypt. On the one hand,
security work typically employs a design technique that seeks to
expose only what is needed. On the other hand, there may be
performance and operational benefits in exposing selected information
to network tools.
Mutable fields in the transport header provide opportunities for
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 may 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.
2.5. Adding Transport Information to Network-Layer Protocol Headers
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The transport 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. This has the advantage that a single
header can support all transport protocols, but there may also be
less desirable implications of separating the operation of the
transport protocol from the measurement framework.
Some measurements may 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) 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.
Another example of a network-layer approach is the IPv6 Performance
and Diagnostic Metrics (PDM) Destination Option [I-D.ietf-ippm-6man-
pdm-option]. 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.
A drawback of using extension headers is that 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. Another 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.
3. Implications of Protecting the Transport Headers
This section explores key implications of working with encrypted
transport protocols.
3.1. 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
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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 becomes important when considering changes to transport
protocols, changes in network infrastructure, or the emergence of new
traffic patterns.
3.2. Characterising "Unknown" Network Traffic
The patterns and types of traffic that share Internet capacity
changes with 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.
3.3. Accountability and Internet Transport Protocols
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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, and where needed to
deploy appropriate tools Section 1.1.2.4. Obfuscating or hiding this
information using encryption is expected to lead operators and
maintainers of middleboxes (firewalls, etc.) to seek other methods to
classify and mechanisms to condition network traffic. A lack of data
seems likely to reduce the level of precision with which these
mechanisms are applied, and this needs to be considered when
evaluating the impact of designs for transport encryption.
3.4. Impact on Research, Development and Deployment
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.
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.
The growth and diversity of applications and protocols using the
Internet continues to expand - and 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 [I-D.ietf-tcpm-dctcp], and methods
proposed for Low Latency Low Loss Scalable throughput, L4S). For
each new method 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.
4. Acknowledgements
The author would like to thank all who have talked to him face-to-
face or via email. ...
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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.
5. Security Considerations
This document is about design and deployment considerations for
transport protocols. 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; no current full-featured standards-track transport protocol
provides these features on its own. Therefore, these features are
not considered in this document, with the exception of native
authentication capabilities of TCP and SCTP for which the security
considerations in RFC4895.
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. Standard protocols
and understanding of the interactions between mechanisms and traffic
patterns can also provide valuable insight into appropriate security
design. Like congestion control mechanisms, security mechanisms are
difficult to design and implement correctly. It is hence recommended
that applications employ well-known standard security mechanisms such
as DTLS, TLS or IPsec, rather than inventing their own.
6. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX
This memo includes no request to IANA.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, <http://www.rfc-editor.org/info/
rfc2119>.
7.2. Informative References
[I-D.dolson-plus-middlebox-benefits]
Dolson, D., Snellman, J., Boucadair, M. and C. Jacquenet,
"Beneficial Functions of Middleboxes", Internet-Draft
draft-dolson-plus-middlebox-benefits-03, March 2017.
[I-D.ietf-aqm-codel]
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Nichols, K., Jacobson, V., McGregor, A. and J. Jana,
"Controlled Delay Active Queue Management", Internet-Draft
draft-ietf-aqm-codel-00, October 2014.
[I-D.ietf-aqm-fq-codel]
Hoeiland-Joergensen, T., McKenney, P., Taht, D., Gettys,
J. and E. Dumazet, "FlowQueue-Codel", Internet-Draft
draft-ietf-aqm-fq-codel-00, January 2015.
[I-D.ietf-aqm-pie]
Pan, R., Natarajan, P., Baker, F. and G. White, "PIE: A
Lightweight Control Scheme To Address the Bufferbloat
Problem", Internet-Draft draft-ietf-aqm-pie-00, October
2014.
[I-D.ietf-ippm-6man-pdm-option]
Elkins, N., Hamilton, R. and m. mackermann@bcbsm.com,
"IPv6 Performance and Diagnostic Metrics (PDM) Destination
Option", Internet-Draft draft-ietf-ippm-6man-pdm-
option-10, May 2017.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Internet-Draft draft-ietf-quic-
transport-03, May 2017.
[I-D.ietf-tcpm-accurate-ecn]
Briscoe, B., Kuehlewind, M. and R. Scheffenegger, "More
Accurate ECN Feedback in TCP", Internet-Draft draft-ietf-
tcpm-accurate-ecn-00, December 2015.
[I-D.ietf-tcpm-dctcp]
Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.
and G. Judd, "Datacenter TCP (DCTCP): TCP Congestion
Control for Datacenters", Internet-Draft draft-ietf-tcpm-
dctcp-06, May 2017.
[I-D.ietf-tsvwg-l4s-arch]
Briscoe, B., Schepper, K. and M. Bagnulo, "Low Latency,
Low Loss, Scalable Throughput (L4S) Internet Service:
Architecture", Internet-Draft draft-ietf-tsvwg-l4s-
arch-00, May 2017.
[I-D.mm-wg-effect-encrypt]
Moriarty, K. and A. Morton, "Effect of Pervasive
Encryption on Operators", Internet-Draft draft-mm-wg-
effect-encrypt-11, April 2017.
[I-D.trammell-plus-abstract-mech]
Trammell, B., "Abstract Mechanisms for a Cooperative Path
Layer under Endpoint Control", Internet-Draft draft-
trammell-plus-abstract-mech-00, September 2016.
[I-D.trammell-plus-statefulness]
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Kuehlewind, M., Trammell, B. and J. Hildebrand,
"Transport-Independent Path Layer State Management",
Internet-Draft draft-trammell-plus-statefulness-02,
December 2016.
[Latency] Briscoe, B., "Reducing Internet Latency: A Survey of
Techniques and Their Merits", November 2014.
[Measure] Fairhurst, G., Kuehlewind, M. and D. Lopez, "Measurement-
based Protocol Design", June 2017.
[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, <http://www.rfc-
editor.org/info/rfc2474>.
[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, <http://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, <http://www.rfc-
editor.org/info/rfc3168>.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002,
<http://www.rfc-editor.org/info/rfc3234>.
[RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G. and M.
Sooriyabandara, "TCP Performance Implications of Network
Path Asymmetry", BCP 69, RFC 3449, DOI 10.17487/RFC3449,
December 2002, <http://www.rfc-editor.org/info/rfc3449>.
[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, <http://www.rfc-editor.org/info/rfc3550>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J. and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004, <http://www
.rfc-editor.org/info/rfc3819>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>.
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[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI
10.17487/RFC4302, December 2005, <http://www.rfc-
editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, DOI 10.17487/RFC4303, December 2005, <http://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, <http://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, <http://www.rfc-
editor.org/info/rfc4737>.
[RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A. and R.
Whitner, "Improved Packet Reordering Metrics", RFC 5236,
DOI 10.17487/RFC5236, June 2008, <http://www.rfc-
editor.org/info/rfc5236>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
RFC5246, August 2008, <http://www.rfc-editor.org/info/
rfc5246>.
[RFC5559] Eardley, P., Ed., "Pre-Congestion Notification (PCN)
Architecture", RFC 5559, DOI 10.17487/RFC5559, June 2009,
<http://www.rfc-editor.org/info/rfc5559>.
[RFC5925] Touch, J., Mankin, A. and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <http://www.rfc-editor.org/info/rfc5925>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://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, <http://www.rfc-editor.org/info/
rfc6437>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <http://www.rfc-editor.org/info/rfc6679>.
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[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <http://www.rfc-editor.org/info/rfc7258>.
[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, <http://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, <http://
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, <http://www.rfc-editor.org/
info/rfc7624>.
[RFC7713] Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)
Concepts, Abstract Mechanism, and Requirements", RFC 7713,
DOI 10.17487/RFC7713, December 2015, <http://www.rfc-
editor.org/info/rfc7713>.
[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, <http://www.rfc-editor.org/info/rfc7928>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers", BCP
208, RFC 8084, DOI 10.17487/RFC8084, March 2017, <http://
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, <http://www.rfc-editor.org/info/rfc8085>.
[RFC8086] Yong, L., Ed., Crabbe, E., Xu, X. and T. Herbert, "GRE-in-
UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, March
2017, <http://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, <http://www.rfc-editor.org/
info/rfc8087>.
[Tor] The Tor Project, ., "https://www.torproject.org", June
2017.
Appendix A. Revision information
Fairhurst & Perkins Expires March 29, 2018 [Page 26]
Internet-Draft Transport Encryption September 2017
-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 contributore 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.
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 March 29, 2018 [Page 27]