Internet DRAFT - draft-arkko-iab-path-signals-collaboration
draft-arkko-iab-path-signals-collaboration
Network Working Group J. Arkko
Internet-Draft Ericsson
Intended status: Informational T. Hardie
Expires: 28 April 2022 Cisco
T. Pauly
Apple
M. Kühlewind
Ericsson
25 October 2021
Considerations on Application - Network Collaboration Using Path Signals
draft-arkko-iab-path-signals-collaboration-01
Abstract
Encryption and other security mechanisms are on the rise on all
layers of the stack, protecting user data and making network
operations more secured. Further, encryption is also a tool to
address ossification that has been observed over time. Separation of
functions into layers and enforcement of layer boundaries based on
encryption supports selected exposure to those entities that are
addressed by a function on a certain layer. A clear separation
supports innovation and also enables new opportunities for
collaborative functions. RFC 8558 describes path signals as messages
to or from on-path elements. This document states principles for
designing mechanisms that use or provide path signals and calls for
actions on specific valuable cases.
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
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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 28 April 2022.
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Copyright Notice
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document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Past Guidance . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Principles . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Intentional Distribution . . . . . . . . . . . . . . . . 6
3.2. Minimum Set of Entities . . . . . . . . . . . . . . . . . 7
3.3. Consent of Parties . . . . . . . . . . . . . . . . . . . 7
3.4. Minimum Information . . . . . . . . . . . . . . . . . . . 8
3.5. Carrying Information . . . . . . . . . . . . . . . . . . 9
3.6. Protecting Information and Authentication . . . . . . . . 9
4. Further Work . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
6. Informative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Encryption, besides its important role in security in general,
provides a tool to control information access and protects again
ossification by avoiding unintended dependencies and requiring active
maintenance. The increased deployment of encryption provides an
opportunity to reconsider parts of Internet architecture that have
rather used implicit derivation of input signals for on-path
functions than explicit signaling, as recommended by RFC 8558
[RFC8558].
RFC 8558 defines the term path signals as signals to or from on-path
elements. Today path signals are often implicit, e.g. derived from
in-clear end-to-end information by e.g. examining transport
protocols. For instance, on-path elements use various fields of the
TCP header [RFC0793] to derive information about end-to-end latency
as well as congestion. These techniques have evolved because the
information was simply available and use of this information is
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easier and therefore also cheaper than any explicit and potentially
complex cooperative approach.
As such, applications and networks have evolved their interaction
without comprehensive design for how this interaction should happen
or which information would be desired for a certain function. This
has lead to a situation where sometimes information is used that
maybe incomplete, incorrect, or only indirectly representative of the
information that was actually desired. In addition, dependencies on
information and mechanisms that were designed for a different
function limits the evolvability of the protocols in question.
The unplanned interaction ends up having several negative effects:
* Ossifying protocols by introducing unintended parties that may not
be updating
* Creating systemic incentives against deploying more secure or
private versions of protocols
* Basing network behaviour on information that may be incomplete or
incorrect
* Creating a model where network entities expect to be able to use
rich information about sessions passing through
For instance, features such as DNS resolution or TLS setup have been
used beyond their original intent, such as in name-based filtering.
MAC addresses have been used for access control, captive portal
implementations that employ taking over cleartext HTTP sessions, and
so on.
Increased deployment of encryption can and will change this
situation. For instance, QUIC replaces TCP for various application
and protects all end-to-end signals to only be accessible by the
endpoint, ensuring evolvability [RFC9000]. QUIC does expose
information dedicated for on-path elements to consume by design
explicit signal for specific use cases, such as the Spin bit for
latency measurements or connection ID that can be used by load
balancers [I-D.ietf-quic-manageability] but information is limited to
only those use cases. Each new use cases requires additional action.
Explicit signals that are specifically designed for the use of on-
path function leave all other information is appropriately protected.
This enables an architecturally clean approach and evolvability,
while allowing an information exchage that is important for improving
the quality of experience for users and efficient management of the
network infrastructure built for them.
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This draft discusses different approaches for explicit collaboration
and provides guidance on architectural principles to design new
mechanisms. Section 2 discusses past guidance. Section 3 discusses
principles that good design can follow. This section also provides
some examples and explanation of situations that not following the
principles can lead to. Section 4 points to topics that need more to
be looked at more carefully before any guidance can be given.
2. Past Guidance
Incentives are a well understood problem in general but perhaps not
fully internalised for various designs attempting to establish
collaboration between applications and path elements. The principle
is that both receiver and sender of information must acquire tangible
and immediate benefits from the communication, such as improved
performance.
A related issue is understanding whether a business model or
ecosystem change is needed. For instance, relative prioritization
between different flows of a user or an application does not require
agreements or payments. But requesting prioritization over other
people's traffic may imply that you have to pay for that which may
not be easy even for a single provider let alone across many.
But on to more technical aspects.
The main guidance in [RFC8558] is to be aware that implicit signals
will be used whether intended or not. Protocol designers should
consider either hiding these signals when the information should not
be visible, or using explicit signals when it should be.
[RFC9049] discusses many past failure cases, a catalogue of past
issues to avoid. It also provides relevant guidelines for new work,
from discussion of incentives to more specific observations, such as
the need for outperforming end-to-end mechanisms (Section 4.4),
considering the need for per-connection state (Section 4.6), taking
into account the latency involved in reacting to distant signals, and
so on.
There are also more general guidance documents, e.g., [RFC5218]
discusses protocol successes and failures, and provides general
advice on incremental deployability etc. Internet Technology
Adoption and Transition (ITAT) workshop report [RFC7305] is also
recommended reading on this same general topic. And [RFC6709]
discusses protocol extensibility, and provides general advice on the
importance of global interoperability and so on.
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3. Principles
This section attempts to provide some architecture-level principles
that would help future designers and recommend useful models to
apply.
A large number of our protocol mechanisms today fall into one of two
categories: authenticated and private communication that is only
visible to the end-to-end nodes; and unauthenticated public
communication that is visible to all nodes on a path. RFC 8558
explores the line between data that is protected and path signals.
There is a danger in taking a position that is too extreme towards
either exposing all information to the path, or hiding all
information from the path.
Exposed information encourages pervasive monitoring, which is
described in RFC 7258 [RFC7258]. Exposed information may also be
used for commercial purposes, or form a basis for filtering that the
applications or users do not desire.
But a lack of all path signaling, on the other hand, may be harmful
to network management, debugging, or the ability for networks to
provide the most efficient services. There are many cases where
elements on the network path can provide beneficial services, but
only if they can coordinate with the endpoints. It also affects the
ability of service providers and others observe why problems occur
[RFC9075].
This situation is sometimes cast as an adversarial tradeoff between
privacy and the ability for the network path to provide intended
functions. However, this is perhaps an unnecessarily polarized
characterization as a zero-sum situation. Not all information
passing implies loss of privacy. For instance, performance
information or preferences do not require disclosing user or
application identity or what content is being accessed, network
congestion status information does not have reveal network topology
or the status of other users, and so on.
This points to one way to resolve the adversity: the careful of
design of what information is passed.
Another approach is to employ explicit trust and coordination between
endpoints and network devices. VPNs are a good example of a case
where there is an explicit authentication and negotiation with a
network path element that's used to optimize behavior or gain access
to specific resources.
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The goal of improving privacy and trust on the Internet does not
necessarily need to remove the ability for network elements to
perform beneficial functions. We should instead improve the way that
these functions are achieved. Our goals should be:
* To ensure that information is distributed intentionally, not
accidentally;
* to understand the privacy and other implications of any
distributed information;
* to ensure that the information distribution targets the intended
parties; and
* to gate the distribution of information on the consent of the
relevant parties
These goals for distribution apply equally to senders, receivers, and
path elements.
We can establish some basic questions that any new network path
functions should consider:
* What is the minimum set of entities that need to be involved?
* What is the minimum information each entity in this set needs?
* Which entities must consent to the information exchange?
If we look at many of the ways network path functions are achieved
today, we find that many if not most of them fall short the standard
set up by the questions above. Too often, they send unnecessary
information or fail to limit the scope of distribution or providing
any negotiation or consent.
Going forward, new standards work in the IETF needs to focus on
addressing this gap by providing better alternatives and mechanisms
for providing path functions. Note that not all of these functions
can be achieved in a way that preserves a high level of user privacy
from the network; in such cases, it is incumbent upon us to not
ignore the use case, but instead to define the high bar for consent
and trust, and thus define a limited applicability for those
functions.
3.1. Intentional Distribution
This guideline is best expressed in RFC 8558:
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"Fundamentally, this document recommends that implicit signals should
be avoided and that an implicit signal should be replaced with an
explicit signal only when the signal's originator intends that it be
used by the network elements on the path. For many flows, this may
result in the signal being absent but allows it to be present when
needed."
This guideline applies also in the other direction as well. For
instance, a network element should not unintentionally leak
information that is visible to endpoints. An explicit decision is
needed for a specific information to be provided, along with analysis
of the security and privacy implications of that information.
3.2. Minimum Set of Entities
It is recommended that a design identify the minimum number of
entities needed to share a specific signal required for an identified
function. In some cases this will be a very limited set, e.g. when
the application needs to provide a signal to a specific gateway
function. In other cases, such as congestion control, a signal might
be shared with every router along the path, since each should be
aware of the congestion.
While it is tempting to consider removing these limitations in the
context of closed, private networks, each interaction is still best
considered separately, rather than simply allowing all information
exchanges within the closed network. Even in a closed network with
carefully managed components there may be compromised components, as
evidenced in the most extreme way by the Stuxnet worm that operated
in an airgapped network. Most "closed" networks have at least some
needs and means to access the rest of the Internet, and should not be
modeled as if they had an impenetrable security barrier.
3.3. Consent of Parties
Consent and trust must determine the distribution of information.
The set of entities that need to consent is determined by the scope
and specificity of the information being shared.
Three distinct types of consent are recommended for collaboration or
information sharing:
* A corollary of the intentional distribution is that the sender
needs to agree to sending the information. Or that the requester
for an action needs to agree to make a request; it should not be
an implicit decision by the receiver that information was sent or
a request was made, just because a packet happened to be formed in
a particular way.
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* At the same time, the recipient of information or the target of a
request should agree to wishing to receive the information. It
should not be burdened with extra processing if it does not have
willigness or a need to do so. This happens naturally in most
protocol designs, but has been a problem for some cases where
"slow path" packet processing is required or implied, and the
recipient or router did not have willingness for this.
* Internet communications are not made for the applications, they
are ultimately made on behalf of users. Information relating to
the users is something that both networks and applications should
be careful with, and not be shared without the user's consent.
This is not always easy, as the interests of the user and (for
instance) application developer may not always coincide; some
applications may wish to collect more information about the user
than the user would like.
As a result, typically an application's consent is not the same as
the user's consent.
3.4. Minimum Information
Parties should provide only the information that is needed for the
other party to perform the collaboration task that is desired by this
party, and not more. This applies to information sent by an
application about itself, information sent about users, or
information sent by the network.
An architecture can follow the guideline from RFC 8558 in using
explicit signals, but still fail to differentiate properly between
information that should be kept private and information that should
be shared.
In looking at what information can or cannot easily be passed, we can
look at both information from the network to the application, and
from the application to the network.
For the application to the network direction, user-identifying
information can be problematic for privacy and tracking reasons.
Similarly, application identity can be problematic, if it might form
the basis for prioritization or discrimination that the that
application provider may not wish to happen. It may also have
undesirable economic consequences, such as extra charges for the
consumer from a priority service where a regular service would have
worked.
On the other hand, as noted above, information about general classes
of applications may be desirable to be given by application
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providers, if it enables prioritization that would improve service,
e.g., differentiation between interactive and non-interactive
services.
For the network to application direction there is similarly sensitive
information, such as the precise location of the user. On the other
hand, various generic network conditions, predictive bandwidth and
latency capabilities, and so on might be attractive information that
applications can use to determine, for instance, optimal strategies
for changing codecs. However, information given by the network about
load conditions and so on should not form a mechanism to provide a
side-channel into what other users are doing.
While information needs to be specific and provided on a per-need
basis, it is often beneficial to provide declarative information
that, for instance, expresses application needs than makes specific
requests for action.
3.5. Carrying Information
There is a distinction between what information is passed and how it
is carried. The actually sent information may be limited, while the
mechanisms for sending or requesting information can be capable of
sending much more.
There is a tradeoff here between flexibility and ensuring the
minimality of information in the future. The concern is that a fully
generic data sharing approach between different layers and parties
could potentially be misused, e.g., by making the availability of
some information a requirement for passing through a network.
This is undesirable, and our recommendation is to employ very
targeted, minimal information carriage mechanisms.
3.6. Protecting Information and Authentication
Some simple forms of information often exist in cleartext form, e.g,
ECN bits from routers are generally not authenticated or integrity
protected. This is possible when the information exchanges are
advisory in their nature, and do not carry any significantly
sensitive information from the parties.
In other cases it may be necessary to establish a secure channel for
communication with a specific other party, e.g., between a network
element and an application. This channel may need to be
authenticated, integrity protected and encrypted. This is necessary,
for instance, if the particular information or request needs to be
share in confidency only with a particular, trusted node, or there's
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a danger of an attack where someone else may forge messages that
could endanger the communication.
However, it is important to note that authentication does not equal
trust. Whether a communication is with an application server or
network element that can be shown to be associated with a particular
domain name, it does not follow that information about the user can
be safely sent to it.
In some cases, the ability of a party to show that it is on the path
can be beneficial. For instance, an ICMP error that refers to a
valid flow may be more trustworthy than any ICMP error claiming to
come from an address.
Other cases may require more substantial assurances. For instance, a
specific trust arrangement may be established between a particular
network and application. Or technologies such as confidential
computing can be applied to provide an assurance that information
processed by a party is handled in an appropriate manner.
4. Further Work
This is a developing field, and it is expected that our understanding
continues to grow. The recent changes with regards to much higher
use of encryption at different protocol layers, the consolidation or
more and more traffic to the same destinations, and so on have also
greatly impacted the field.
While there are some examples of modern, well-designed collaboration
mechanisms, clearly more work is needed. Many complex cases would
require significant developments in order to become feasible.
Some of the most difficult areas are listed below. Research on these
topics would be welcome.
* Business arrangements. Many designs - for instance those related
to quality-of-service - involve an expectation of paying for a
service. This is possible and has been successful within
individual domains, e.g., users can pay for higher data rates or
data caps in their ISP networks. However, it is a business-wise
much harder proposition for end-to-end connections across multiple
administrative domains [Claffy2015] [RFC9049].
* Secure communications with path elements. This has been a
difficult topic, both from the mechanics and scalability point
view, but also because there is no easy way to find out which
parties to trust or what trust roots would be appropriate. Some
application-network element interaction designs have focused on
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information (such as ECN bits) that is distributed openly within a
path, but there are limited examples of designs with secure
information exchange with specific nodes.
* The use of path signals for reducing the effects of denial-of-
service attacks, e.g., in the form of modern "source quench"
designs.
* Ways of protecting information when held by network elements or
servers, beyond communications security. For instance, host
applications commonly share sensitive information about the user's
actions with other nodes, starting from basic data such as domain
names learned by DNS infrastructure or source and destination
addresses and protocol header information learned by all routers
on the path, to detailed end user identity and other information
learned by the servers. Some solutions are starting to exist for
this but are not widely deployed, at least not today [Oblivious]
[PDoT] [I-D.arkko-dns-confidential] [I-D.thomson-http-oblivious].
These solutions address also very specific parts of the issue, and
more work remains.
* Sharing information from networks to applications. Some proposals
have been made in this space (see, e.g.,
[I-D.flinck-mobile-throughput-guidance]) but there are no
successful or deployed mechanisms today.
5. Acknowledgments
The authors would like to thank everyone at the IETF, the IAB, and
our day jobs for interesting thoughts and proposals in this space.
Fragments of this document were also in
[I-D.per-app-networking-considerations] and
[I-D.arkko-path-signals-information] that were published earlier. We
would also like to acknowledge [I-D.trammell-stackevo-explicit-coop]
for presenting similar thoughts. Finally, the authors would like to
thank Adrian Farrell, Toerless Eckert, and Jeffrey Haas for useful
feedback in the IABOPEN session at IETF-111.
6. Informative References
[Claffy2015]
kc Claffy, . and D. Clark, "Adding Enhanced Services to
the Internet: Lessons from History", TPRC 43: The 43rd
Research Conference on Communication, Information and
Internet Policy Paper , April 2015.
[I-D.arkko-dns-confidential]
Arkko, J. and J. Novotny, "Privacy Improvements for DNS
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Resolution with Confidential Computing", Work in Progress,
Internet-Draft, draft-arkko-dns-confidential-02, 2 July
2021, <https://www.ietf.org/archive/id/draft-arkko-dns-
confidential-02.txt>.
[I-D.arkko-path-signals-information]
Arkko, J., "Considerations on Information Passed between
Networks and Applications", Work in Progress, Internet-
Draft, draft-arkko-path-signals-information-00, 22
February 2021, <https://www.ietf.org/archive/id/draft-
arkko-path-signals-information-00.txt>.
[I-D.flinck-mobile-throughput-guidance]
Jain, A., Terzis, A., Flinck, H., Sprecher, N.,
Arunachalam, S., Smith, K., Devarapalli, V., and R. B.
Yanai, "Mobile Throughput Guidance Inband Signaling
Protocol", Work in Progress, Internet-Draft, draft-flinck-
mobile-throughput-guidance-04, 13 March 2017,
<https://www.ietf.org/archive/id/draft-flinck-mobile-
throughput-guidance-04.txt>.
[I-D.ietf-quic-manageability]
Kuehlewind, M. and B. Trammell, "Manageability of the QUIC
Transport Protocol", Work in Progress, Internet-Draft,
draft-ietf-quic-manageability-13, 2 September 2021,
<https://www.ietf.org/archive/id/draft-ietf-quic-
manageability-13.txt>.
[I-D.per-app-networking-considerations]
Colitti, L. and T. Pauly, "Per-Application Networking
Considerations", Work in Progress, Internet-Draft, draft-
per-app-networking-considerations-00, 15 November 2020,
<https://www.ietf.org/archive/id/draft-per-app-networking-
considerations-00.txt>.
[I-D.thomson-http-oblivious]
Thomson, M. and C. A. Wood, "Oblivious HTTP", Work in
Progress, Internet-Draft, draft-thomson-http-oblivious-02,
24 August 2021, <https://www.ietf.org/archive/id/draft-
thomson-http-oblivious-02.txt>.
[I-D.trammell-stackevo-explicit-coop]
Trammell, B., "Architectural Considerations for Transport
Evolution with Explicit Path Cooperation", Work in
Progress, Internet-Draft, draft-trammell-stackevo-
explicit-coop-00, 23 September 2015,
<https://www.ietf.org/archive/id/draft-trammell-stackevo-
explicit-coop-00.txt>.
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[Oblivious]
Schmitt, P., "Oblivious DNS: Practical privacy for DNS
queries", Proceedings on Privacy Enhancing Technologies
2019.2: 228-244 , 2019.
[PDoT] Nakatsuka, Y., Paverd, A., and G. Tsudik, "PDoT: Private
DNS-over-TLS with TEE Support", Digit. Threat.: Res.
Pract., Vol. 2, No. 1, Article 3,
https://dl.acm.org/doi/fullHtml/10.1145/3431171 , February
2021.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful
Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,
<https://www.rfc-editor.org/info/rfc5218>.
[RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
DOI 10.17487/RFC6709, September 2012,
<https://www.rfc-editor.org/info/rfc6709>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7305] Lear, E., Ed., "Report from the IAB Workshop on Internet
Technology Adoption and Transition (ITAT)", RFC 7305,
DOI 10.17487/RFC7305, July 2014,
<https://www.rfc-editor.org/info/rfc7305>.
[RFC8558] Hardie, T., Ed., "Transport Protocol Path Signals",
RFC 8558, DOI 10.17487/RFC8558, April 2019,
<https://www.rfc-editor.org/info/rfc8558>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9049] Dawkins, S., Ed., "Path Aware Networking: Obstacles to
Deployment (A Bestiary of Roads Not Taken)", RFC 9049,
DOI 10.17487/RFC9049, June 2021,
<https://www.rfc-editor.org/info/rfc9049>.
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[RFC9075] Arkko, J., Farrell, S., Kühlewind, M., and C. Perkins,
"Report from the IAB COVID-19 Network Impacts Workshop
2020", RFC 9075, DOI 10.17487/RFC9075, July 2021,
<https://www.rfc-editor.org/info/rfc9075>.
Authors' Addresses
Jari Arkko
Ericsson
Email: jari.arkko@ericsson.com
Ted Hardie
Cisco
Email: ted.ietf@gmail.com
Tommy Pauly
Apple
Email: tpauly@apple.com
Mirja Kühlewind
Ericsson
Email: mirja.kuehlewind@ericsson.com
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