The Impact of Transport Header Confidentiality on Network Operation and Evolution of the Internet
draft-fairhurst-tsvwg-transport-encrypt-07
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| Authors | Gorry Fairhurst , Colin Perkins | ||
| Last updated | 2018-04-10 | ||
| Replaced by | draft-ietf-tsvwg-transport-encrypt, draft-ietf-tsvwg-transport-encrypt, RFC 9065 | ||
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draft-fairhurst-tsvwg-transport-encrypt-07
TSVWG G. Fairhurst
Internet-Draft University of Aberdeen
Intended status: Informational C.S. Perkins
Expires: October 10, 2018 University of Glasgow
April 10, 2018
The Impact of Transport Header Confidentiality on Network Operation and
Evolution of the Internet
draft-fairhurst-tsvwg-transport-encrypt-07
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 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 http://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 October 10, 2018.
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 (http://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
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Current uses of Transport Headers within the Network . . . . . 8
2.1. Observing Transport Information in the Network . . . . . . 9
2.1.1. Flow Identification . . . . . . . . . . . . . . . . . 9
2.1.2. Metrics derived from Transport Layer Headers . . . . . 10
2.1.3. Metrics derived from Network Layer Headers . . . . . . 12
2.2. Transport Measurement . . . . . . . . . . . . . . . . . . 14
2.2.1. Point of Measurement . . . . . . . . . . . . . . . . . 14
2.2.2. Use by Operators to Plan and Provision Networks . . . 15
2.2.3. Service Performance Measurement . . . . . . . . . . . 15
2.2.4. Measuring Transport to Support Network Operations . . 16
2.3. Use for Network Diagnostics and Troubleshooting . . . . . 17
2.3.1. Examples of measurements . . . . . . . . . . . . . . . 18
2.4. Observing Headers to Implement Network Policy . . . . . . 19
3. Encryption and Authentication of Transport Headers . . . . . . 19
3.1. Authenticating the Transport Protocol Header . . . . . . . 21
3.2. Encrypting the Transport Payload . . . . . . . . . . . . . 21
3.3. Encrypting the Transport Header . . . . . . . . . . . . . 21
3.4. Authenticating Transport Information and Selectively
Encrypting the Transport Header . . . . . . . . . . . . . 22
3.5. Optional Encryption of Header Information . . . . . . . . 22
4. Addition of Transport Information to Network-Layer Protocol
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5. Implications of Protecting the Transport Headers . . . . . . . 23
5.1. Independent Measurement . . . . . . . . . . . . . . . . . 23
5.2. Characterising "Unknown" Network Traffic . . . . . . . . . 24
5.3. Accountability and Internet Transport Protocols . . . . . 24
5.4. Impact on Research, Development and Deployment . . . . . . 25
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 26
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 29
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.1. Normative References . . . . . . . . . . . . . . . . . . 29
10.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Revision information . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
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This document describes implications 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 expected
implications of transport protocol design and network operation. It
also considers anticipated implications on transport and application
evolution.
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
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 (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 about the interference
with Internet traffic have led to a rapidly expanding deployment of
encryption to protect end-user privacy, in protocols like QUIC [I-D
.ietf-quic-transport], but also expected to form a basis of future
protocol designs.
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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 packet headers 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
to the protocol (e.g., recognising the start of a connection), but
not in all cases (e.g., a mechanism implemented in a network device,
such as a firewall, could require a header field to have only a
specific known set of values could prevent the device from forwarding
packets using a different version of a protocol that introduces a new
feature that changes the value present in this field).
A protocol design can use header encryption to provide
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 imply 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 may change in future protocols, or that
methods that utilise the information are robust to potential changes
as protocols evolve over time. To avoid unwanted inspection, a
protocol could also intentionally vary the format and value of header
fields (sometimes known as Greasing [I-D.thomson-quic-grease]).
At the same time, 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
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hide transport header information from the network. This present
architectural challenges and considerations in the way transport
protocols are designed, and ability to characterise and compare
different transport solutions [Measure].
A level of ossification of the header can be advantageous in terms of
providing a set of specified header fields that become observable by
in-network devices. This results in trade-offs around
authentication, and confidentiality of transport protocol headers and
the potential support for other uses of this header information. 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.
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
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 allowing some measurement.
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 may result in less-efficient identification of
unwanted traffic or development of different methods (e.g. rate-
limiting of uncharacterised traffic).
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Network Troubleshooting and Diagnostics: Encrypting transport header
information eliminates the incentive for operators to troubleshoot
what they cannot interpret. 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 may
imply "don't touch" to some, and could limit a trouble-shooting
response to "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
(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
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 may, 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. For example, one approach could be to employ an
existing transport protocol that reveals little information (e.g.,
UDP), and perform traditional transport functions at higher layers
protecting the confidentiality of transport information. Such a
design, 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 performance cannot be
independently verified by all parties. The ability of other
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stakeholders to review code can help develop deeper insight. In
the heterogeneous Internet, this helps extend the range of
topologies, vendor equipment, and traffic patterns that are
evaluated.
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
important to demonstrate regulatory compliance in some
jurisdictions, and provides an important 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.
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: The 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, 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 [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
ICCRG, and research publications in reviewing new transport
mechanisms and assessing the impact of their experimental
deployment)
In summary, there are tradeoffs. On the one hand, 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.
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. Any new Internet
transport need to provide appropriate transport mechanisms and
operational support to assure the resulting traffic can not result in
persistent congestion collapse [RFC2914]. This document suggests
that the balance between information exposed and concealed should be
carefully considered when specifying new protocols.
2. Current uses of Transport Headers within the Network
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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 [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.
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].
2.1. 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 needs to be known to
be observed. IETF transport protocols specify this information.
The following subsections describe various ways that observable
transport information may be utilised.
2.1.1. Flow Identification
Transport protocol header information (together with information in
the network header), 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) transport port number 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
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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 can instead be
identified by signalling protocols or through the use of magic
numbers placed in the first byte(s) of the datagram payload.
Flow identification is more complex and less easily achieved when
multiplexing is used at or above the transport layer.
2.1.2. 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 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:
Traffic Rate and Volume: Header information e.g., (sequence number,
length) 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
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 (providing detail of trends rather than the
volume per subscriber).
Loss Rate and Loss Pattern: Flow loss rate may be derived (e.g., from
sequence number) and is often used as a metric for performance
assessment and to characterise transport behaviour. Understanding
the root cause of loss can help an operator determine whether this
requires corrective action. Network operators may also use the
variation in patterns of loss as a 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), inadequate
provision of traffic preemption. 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 node/segment at the time of loss.
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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, 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 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.
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
point in the network to determine not only the path RTT, but also
to measure the upstream and downstream contribution to the RTT.
This can be used to locate a source of latency, e.g., by observing
cases where the ratio of median to minimum RTT is large for a part
of a path.
The service offered by 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]
[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.
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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 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
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.
Operational tools to detect mis-ordered packet flows and quantify the
degree or reordering. Key performance indicators are retransmission
rate, packet drop rate, sector utilisation level, a measure of
reordering, peak rate, the CE-marking rate, etc.
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 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.
2.1.3. 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
utilised to make flow observations.
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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 performance data.
Use Network-Layer Differentiated Services Code Point Point: Applicati
ons 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 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 are carried in the IP protocol header, it is much easier
to measure ECN than to measure 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 [RFC8257], and Low Latency Low Loss Scalable
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throughput, L4S, [I-D.ietf-tsvwg-l4s-arch].
Use of ECN requires 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].
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].
2.2. 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
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 [I-D.mm-wg-effect-
encrypt].
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.
2.2.1. Point of Measurement
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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 a 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 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.).
2.2.2. 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 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 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.
2.2.3. 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
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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 2.2.1.
However, passive measurements may rely on observing transport
headers.
2.2.4. 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 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 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
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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 datagram 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 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 2.1.2.
2.3. 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.
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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 reduce
the ability for networks to "help" (e.g., in response to tracing
issues, making appropriate 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 for tools 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, and
this may require alternative tools may need to be developed and
deployed.
2.3.1. Examples of measurements
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 inverstigation after an anompoly 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 bandwidth tests in a mobile network are obvious). Some active
measurements (e.g., response under load or particular workloads)
perturb other traffic, and could require dedicated access to the
network segment. An alternative approach is to use in-network
techniques that observe transport packet headers in operational
networks to make the measurements.
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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.
2.4. 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 management of the QoS or Quality of Experience (QoE) in 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.
3. 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.
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
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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
protect identity, user location, and defend against traffic
analysis, and have used methods such as IPsec ESP. Revelations
about the use of pervasive surveillance [RFC7624] have, to some
extent, eroded trust in the service offered by network operators,
and following the Snowden revelation in the USA in 2013 has led to
an increased desire for people to employ encryption to avoid
unwanted "eavesdropping" on their communications. Concerns have
also been voiced about the addition of information to packets by
third parties to provide analytics, customization, advertising,
cross-site tracking of users, to bill the customer, or to
selectively allow or block content. Whatever the reasons, there
are now activities in the IETF to design new protocols that may
include some form of transport header encryption (e.g., QUIC [I-D
.ietf-quic-transport]).
Authentication methods (that provide integrity checks of protocols
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], the DSCP and ECN.
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 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.
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The next subsections briefly review some security design options for
transport protocols.
3.1. 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] 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.
3.2. 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
header fields could be protected by combining this with an integrity
check (Section 3.1).
Examples of encrypting the payload include Transport Layer Security
(TLS) over TCP [RFC5246] [RFC7525] or Datagram TLS (DTLS) over UDP
[RFC6347] [RFC7525].
3.3. 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 a 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)
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methods also encrypt these headers.
3.4. 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.
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.
3.5. 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 sent with the same level of confidentiality or integrity
protection.
4. 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. 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 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
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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.
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.
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 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.
5. Implications of Protecting the Transport Headers
The choice of which fields to expose and which to encrypt is a design
choice for the transport protocol. Any selective encryption method
requires trading two conflicting goals for a transport protocol
designer to decide which header fields to encrypt. Security work
typically employs a design technique that seeks to expose only what
is needed. However, there can be performance and operational
benefits in exposing selected information to network tools.
This section explores key implications of working with encrypted
transport protocols.
5.1. Independent Measurement
Independent observation by multiple actors is important for
scientific analysis. Encrypting transport header encryption changes
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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 becomes important when considering changes to transport
protocols, changes in network infrastructure, or the emergence of new
traffic patterns.
5.2. 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.
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5.3. Accountability and Internet Transport Protocols
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 2.2.4. 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 reduces the level of precision with which mechanisms
are applied, and this needs to be considered when evaluating the
impact of designs for transport encryption. This could lead to
increased use of rate limiting, circuit breaker techniques [RFC8084],
or even blocking of uncharacterised traffic. This would hinder
deployment of new mechanisms and/or protocols.
5.4. Impact on Research, Development and Deployment
The majority of present Internet applications use two well-known
transport protocols: e.g., TCP and UDP. Although TCP represents the
majority of current traffic, some important real-time applications
use UDP, and much of this traffic utilises RTP format headers in the
payload of the UDP datagram. Since these protocol headers have been
fixed for decades, a range of tools and analysis methods have became
common and well-understood. Over this period, the transport protocol
headers have mostly changed slowly, and so also the need to develop
tools track new versions of the protocol.
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 undetected modification of protocol fields by
network devices, whereas encryption and obfuscation can further
prevent these headers being utilised by network devices. Hiding
headers can therefore provide the opportunity for greater freedom to
update the protocols and can ease experimentation with new techniques
and their final deployment in endpoints.
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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.
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.
6. Conclusions
The majority of present Internet applications use two well-known
transport protocols: e.g., TCP and UDP. Although TCP represents the
majority of current traffic, some important real-time applications
have used 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.
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Confidentiality and strong integrity checks have properties that are
being incorporated into new protocols and which have important
benefits. The pace of development of transports using the WebRTC
data channel and the rapid deployment of QUIC prototype transports
can both be attributed to using a combination of UDP transport and
confidentiality of the UDP payload.
The traffic that can be observed by devices in a network 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 an operational issue 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 needs to be
developed to catch-up with the changes. If the currently deployed
tools and methods are no longer relevant and performance may not be
correctly measured. 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.
A 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. Several scenarios
to illustrate different ways this could evolve are provided below:
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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 level of ossification
allows an operator to establish tooling and procedures that allow
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).
The transport information can be used by operators to provide
troubleshooting, easement and any necessary functions for 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
information forces network operators to act independently from
apps/transport developments to provide the transport information
they need. A range of approaches may proliferate, as in current
networks, 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. 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 outcome 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.
7. 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.
8. 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.
9. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX
This memo includes no request to IANA.
10. References
10.1. 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>.
10.2. 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. Iyengar,
"Controlled Delay Active Queue Management", Internet-Draft
draft-ietf-aqm-codel-10, October 2017.
[I-D.ietf-aqm-fq-codel]
Hoeiland-Joergensen, T., McKenney, P.,
dave.taht@gmail.com, d., Gettys, J. and E. Dumazet, "The
FlowQueue-CoDel Packet Scheduler and Active Queue
Management Algorithm", Internet-Draft draft-ietf-aqm-fq-
codel-06, March 2016.
[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-10, September
2016.
[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-13, June 2017.
[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", Internet-Draft draft-ietf-
ippm-ioam-data-02, March 2018.
[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-06, March 2018.
[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-01, October 2017.
[I-D.mm-wg-effect-encrypt]
Moriarty, K. and A. Morton, "Effects of Pervasive
Encryption on Operators", Internet-Draft draft-mm-wg-
effect-encrypt-24, March 2018.
[I-D.thomson-quic-grease]
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Thomson, M., "More Apparent Randomization for QUIC",
Internet-Draft draft-thomson-quic-grease-00, December
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]
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.
[RFC1273] Schwartz, M.F., "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, <http://www.rfc-
editor.org/info/rfc2474>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC
2914, DOI 10.17487/RFC2914, September 2000, <https://www
.rfc-editor.org/info/rfc2914>.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z.
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>.
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[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393, DOI
10.17487/RFC3393, November 2002, <https://www.rfc-
editor.org/info/rfc3393>.
[RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G. and M.
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>.
[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>.
[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>.
[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>.
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[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[RFC8257] Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.
and G. Judd, "Data Center TCP (DCTCP): TCP Congestion
Control for Data Centers", RFC 8257, DOI 10.17487/RFC8257,
October 2017, <https://www.rfc-editor.org/info/rfc8257>.
[Tor] The Tor Project, ., "https://www.torproject.org", June
2017.
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.
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-07 Updated following comments from Al Morton, Chris Seal, and other
feedback via email.
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//
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