Internet Architecture Board (IAB) J. Arkko

Internet Architecture Board (IAB) J. Arkko
Request for Comments: 9419 Ericsson
Category: Informational T. Hardie
ISSN: 2070-1721 Cisco
T. Pauly
Apple
M. Kühlewind
Ericsson
July 2023

Considerations on Application - Network Collaboration Using Path Signals

Abstract

This document discusses principles for designing mechanisms that use
or provide path signals and calls for standards action in specific
valuable cases. RFC 8558 describes path signals as messages to or
from on-path elements and points out that visible information will be
used whether or not it is intended as a signal. The principles in
this document are intended as guidance for the design of explicit
path signals, which are encouraged to be authenticated and include a
minimal set of parties to minimize information sharing. These
principles can be achieved through mechanisms like encryption of
information and establishing trust relationships between entities on
a path.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Architecture Board (IAB)
and represents information that the IAB has deemed valuable to
provide for permanent record. It represents the consensus of the
Internet Architecture Board (IAB). Documents approved for
publication by the IAB are not candidates for any level of Internet
Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9419.

Copyright Notice

Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.

Table of Contents

1. Introduction
2. Principles
2.1. Intentional Distribution
2.2. Control of the Distribution of Information
2.3. Protecting Information and Authentication
2.4. Minimize Information
2.5. Limiting Impact of Information
2.6. Minimum Set of Entities
2.7. Carrying Information
3. Further Work
4. IANA Considerations
5. Security Considerations
6. Informative References
IAB Members at the Time of Approval
Acknowledgments
Authors' Addresses

1. Introduction

[RFC8558] defines the term "path signals" as signals to or from on-
path elements. Today, path signals are often implicit; for example,
they are derived from cleartext end-to-end information by, e.g.,
examining transport protocols. For instance, on-path elements use
various fields of the TCP header [RFC9293] to derive information
about end-to-end latency as well as congestion. These techniques
have evolved because the information was available and its use
required no coordination with anyone. This made such techniques more
easily deployable than alternative, potentially more explicit or
cooperative, approaches.

However, this also means that applications and networks have often
evolved their interaction without comprehensive design for how this
interaction should happen or which (minimal) information would be
needed for a certain function. This has led to a situation where
information that happens to be easily available is used instead of
the information that is actually needed. As such, that information
may be incomplete, incorrect, or only indirectly representative of
the information that is actually needed. In addition, dependencies
on information and mechanisms that were designed for a different
function limit the evolvability of the protocols in question.

In summary, such unplanned interactions end up having several
negative effects:

* Ossifying protocols by introducing dependencies to unintended
parties that may not be updating, such as how middleboxes have
limited the use of TCP options

* Creating systemic incentives against deploying more secure or
otherwise updated versions of protocols

* Basing network behavior 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.
Media Access Control (MAC) addresses have been used for access
control, captive portals have been used to take over cleartext HTTP
sessions, and so on. (This document is not about whether those
practices are good or bad; it is simply stating a fact that the
features were used beyond their original intent.)

Many protocol mechanisms throughout the stack fall into one of two
categories: authenticated private communication that is only visible
to a very limited set of parties, often one on each "end", and
unauthenticated public communication that is visible to all network
elements on a path.

Exposed information encourages pervasive monitoring, which is
described in [RFC7258]. It may also be used for commercial purposes
or to form a basis for filtering that the applications or users do
not desire. However, a lack of all path signaling, on the other
hand, may limit network management, debugging, or the ability for
networks to optimize their 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 to observe why problems occur
[RFC9075].

As such, this situation is sometimes cast as an adversarial trade-off
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 the
content being accessed, the user identity, or the application in use.
Similarly, network congestion status information does not have to
reveal network topology, the status of other users, and so on.

Increased deployment of encryption is changing this situation.
Encryption provides tools for controlling information access and
protects against 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 used implicit derivation of input signals for on-path
functions rather than explicit signaling, as recommended by
[RFC8558].

For instance, QUIC replaces TCP for various applications and protects
end-to-end signals so that they are only accessible by the endpoints,
ensuring evolvability [RFC9000]. QUIC does expose information
dedicated for on-path elements to consume by using explicit signals
for specific use cases, such as the Spin Bit for latency measurements
or connection ID that can be used by load balancers [RFC9312]. This
information is accessible by all on-path devices, but information is
limited to only those use cases. Each new use case requires
additional action. This points to one way to resolve the adversity:
the careful design of what information is passed.

Another extreme is to employ explicit trust and coordination between
specific entities, endpoints, and network path elements. VPNs are a
good example of a case where there is an explicit authentication and
negotiation with a network path element that is used to gain access
to specific resources. Authentication and trust must be considered
in both directions: how endpoints trust and authenticate signals from
network path elements and how network path elements trust and
authenticate signals from endpoints.

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 and design new ways to support explicit
collaboration where it is seen as beneficial. As such, our goals
should be to:

* ensure that information is distributed intentionally, not
accidentally;

* understand the privacy and other implications of any distributed
information;

* ensure that the information distribution is limited to the
intended parties; and

* gate the distribution of information on the participation of the
relevant parties.

These goals for exposure and distribution apply equally to senders,
receivers, and path elements.

Going forward, new standards work in the IETF needs to focus on
addressing this gap by providing better alternatives and mechanisms
for building functions that require some collaboration between
endpoints and path elements.

We can establish some basic questions that any new network function
should consider:

* Which entities must consent to the information exchange?

* What is the minimum information each entity in this set needs?

* What is the effect that new signals should have?

* What is the minimum set of entities that need to be involved?

* What are the right mechanism and needed level of trust to convey
this kind of information?

If we look at ways network functions are achieved today, we find that
many, if not most of them, fall short of the standard set up by the
questions above. Too often, they send unnecessary information, fail
to limit the scope of distribution, or fail to provide any
negotiation or consent.

Designing explicit signals between applications and network elements,
and ensuring that all information is appropriately protected, enables
information exchange in both directions that is important for
improving the quality of experience and network management. The
clean separation provided by explicit signals is also more conducive
to protocol evolvability.

Beyond the recommendation in [RFC8558], the IAB has provided further
guidance on protocol design. Among other documents, [RFC5218]
provides general advice on incremental deployability based on an
analysis of successes and failures, and [RFC6709] discusses protocol
extensibility. The Internet Technology Adoption and Transition
(ITAT) workshop report [RFC7305] is also a recommended reading on
this same general topic. [RFC9049], an IRTF document, provides a
catalog of past issues to avoid and discusses incentives for adoption
of path signals such as the need for outperforming end-to-end
mechanisms or considering per-connection state.

This document discusses different approaches for explicit
collaboration and provides guidance on architectural principles to
design new mechanisms. Section 2 discusses principles that good
design can follow. This section also provides examples and explores
the consequences of not following these principles in those examples.
Section 3 points to topics that need to be looked at more carefully
before any guidance can be given.

2. Principles

This section provides architecture-level principles for protocol
designers and recommends models to apply for network collaboration
and signaling.

While [RFC8558] focuses specifically on communication to "on-path
elements", the principles described in this document apply
potentially to:

* on-path signaling (in either direction) and

* signaling with other elements in the network that are not directly
on-path but still influence end-to-end connections.

An example of on-path signaling is communication between an endpoint
and a router on a network path. An example of signaling with another
network element is communication between an endpoint and a network-
assigned DNS server, firewall controller, or captive portal API
server. Note that these communications are conceptually independent
of the base flow, even if they share a packet; they are coming from
and going to other parties, rather than creating a multiparty
communication.

Taken together, these principles focus on the inherent privacy and
security concerns of sharing information between endpoints and
network elements, emphasizing that careful scrutiny and a high bar of
consent and trust need to be applied. Given the known threat of
pervasive monitoring, the application of these principles is critical
to ensuring that the use of path signals does not create a
disproportionate opportunity for observers to extract new data from
flows.

2.1. Intentional Distribution

The following guideline is best expressed in [RFC8558]:

| 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.

The goal is that any information should be provided knowingly, for a
specific purpose, sent in signals designed for that purpose, and that
any use of information should be done within that purpose. In
addition, an analysis of the security and privacy implications of the
specific purpose and associated information is needed.

This guideline applies in the network element to application
direction as well: a network element should not unintentionally leak
information. While this document makes recommendations that are
applicable to many different situations, it is important to note that
the above call for careful analysis is key. Different types of
information, applications, and directions of communication influence
the analysis and can lead to very different conclusions about what
information can be shared and with whom. For instance, it is easy to
find examples of information that applications should not share with
network elements (e.g., content of communications) or that network
elements should not share with applications (e.g., detailed user
location in a wireless network). But, equally, information about
other things, such as the onset of congestion, should be possible to
share and can be beneficial information to all parties.

Intentional distribution is a precondition for explicit collaboration
that enables each entity to have the highest possible level of
control about what information to share.

2.2. Control of the Distribution of Information

Explicit signals are not enough. The entities also need to agree to
exchange the information. Trust and mutual agreement between the
involved entities must determine the distribution of information in
order to give each entity adequate control over the collaboration or
information sharing. This can be achieved as discussed below.

The sender needs to decide that it is willing to send information to
a specific entity or set of entities. Any passing of information or
request for an action needs to be explicit and use signaling
mechanisms that are designed for the purpose. Merely sending a
particular kind of packet to a destination should not be interpreted
as an implicit agreement.

At the same time, the recipient of information or the target of a
request should have the option to agree or deny to receiving the
information. It should not be burdened with extra processing if it
does not have willingness or a need to do so. This happens naturally
in most protocol designs, but it has been a problem for some cases
where "slow path" packet processing is required or implied, and the
recipient or router is not willing to handle it. Performance impacts
like this are best avoided, however.

In any case, all involved entities must be identified and potentially
authenticated if trust is required as a prerequisite to share certain
information.

Many Internet communications are not performed on behalf of the
applications but are ultimately made on behalf of users. However,
not all information that may be shared directly relates to user
actions or other sensitive data. All shared information must be
evaluated carefully to identify potential privacy implications for
users. Information that directly relates to the user should not be
shared without the user's consent. It should be noted that the
interests of the user and other parties, such as the application
developer, may not always coincide; some applications may wish to
collect more information about the user than the user would like. As
discussed in [RFC8890], from an IETF point of view, the interests of
the user should be prioritized over those of the application
developer. The general issue of how to achieve a balance of control
between the actual user and an application representing a user's
interest is out of scope for this document.

2.3. Protecting Information and Authentication

Some simple forms of information often exist in cleartext form, e.g.,
Explicit Congestion Notification (ECN) bits from routers are
generally not authenticated or integrity protected. This is possible
when the information exchanges do not carry any significantly
sensitive information from the parties. Often, these kinds of
interactions are also advisory in their nature (see Section 2.5).

In other cases, it may be necessary to establish a secure signaling
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 confidential. This is
necessary, for instance, if the particular information or request
needs to be shared in confidence only with a particular, trusted
network element or endpoint or if there is danger of an attack where
someone else may forge messages that could endanger the
communication.

Authenticated integrity protections on signaled data can help ensure
that data received in a signal has not been modified by other
parties. Still, both network elements and endpoints need to be
careful in processing or responding to any signal. Whether through
bugs or attacks, the content of path signals can lead to unexpected
behaviors or security vulnerabilities if not properly handled. As a
result, the advice in Section 2.5 still applies even in situations
where there's a secure channel for sending information.

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.

2.4. Minimize Information

Each party should provide only the information that is needed for the
other parties to perform the task for which collaboration is desired
and no more. This applies to information sent by an application
about itself, sent about users, or sent by the network. This also
applies to any information related to flow identification.

An architecture can follow the guideline from [RFC8558] in using
explicit signals but still fail to differentiate properly between
information that should be kept private and information that should
be shared. [RFC6973] also outlines this principle of data
minimization as a mitigation technique to protect privacy and
provides further guidance.

In looking at what information can or cannot be easily passed, we
need to consider both information from the network to the application
and from the application to the network.

For the application-to-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 application
provider may not wish to happen.

On the other hand, as noted above, information about general classes
of applications may be desirable to be given by application 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 and then makes
specific requests for action.

2.5. Limiting Impact of Information

Information shared between a network element and an endpoint of a
connection needs to have a limited impact on the behavior of both
endpoints and network elements. Any action that an endpoint or
network element takes based on a path signal needs to be considered
appropriately based on the level of authentication and trust that has
been established, and it needs to be scoped to a specific network
path.

For example, an ICMP signal from a network element to an endpoint can
be used to influence future behavior on that particular network path
(such as changing the effective packet size or closing a path-
specific connection) but should not be able to cause a multipath or
migration-capable transport connection to close.

In many cases, path signals can be considered advisory information,
with the effect of optimizing or adjusting the behavior of
connections on a specific path. In the case of a firewall blocking
connectivity to a given host, endpoints should only interpret that as
the host being unavailable on that particular path; this is in
contrast to an end-to-end authenticated signal, such as a DNSSEC-
authenticated denial of existence [RFC7129].

2.6. Minimum Set of Entities

It is recommended that a design identifies the minimum number of
entities needed to share a specific signal required for an identified
function.

Often, this will be a very limited set, such as when an application
only needs to provide a signal to its peer at the other end of the
connection or a host needs to contact a specific VPN gateway. In
other cases, a broader set is needed, such as when explicit or
implicit signals from a potentially unknown set of multiple routers
along the path inform the endpoints about 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 elements, there may be compromised components, as
evidenced in the most extreme way by the Stuxnet worm that operated
in an air-gapped 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.

2.7. Carrying Information

There is a distinction between what information is sent and how it is
sent. The information that is actually sent may be limited, while
the mechanisms for sending or requesting information can be capable
of sharing much more.

There is a trade-off here between flexibility and ensuring that the
information is minimal 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, such as
making it mandatory to identify specific applications or users. This
is undesirable.

This document recommends that signaling mechanisms that send
information be built to specifically support sending the necessary,
minimal set of information (see Section 2.4) and no more. As
previously noted, flow-identifying information is a path signal in
itself, and as such, provisioning of flow identifiers also requires
protocol-specific analysis.

Further, such mechanisms also need to have the ability to establish
an agreement (see Section 2.2) and sufficient trust to pass the
information (see Section 2.3).

3. Further Work

This is a developing field, and it is expected that our understanding
of it will continue to grow. One recent change is much higher use of
encryption at different protocol layers. This obviously impacts the
field greatly, by removing the ability to use most implicit signals.
However, it may also provide new tools for secure collaboration and
force a rethinking of how collaboration should be performed.

While there are some examples of modern, well-designed collaboration
mechanisms, the list of examples is not long. Clearly, more work is
needed if we wish to realize the potential benefits of collaboration
in further cases. This requires a mindset change, a migration away
from using implicit signals. And of course we need to choose such
cases where the collaboration can be performed safely, where it is
not a privacy concern, and where the incentives of the relevant
parties are aligned. It should also be noted that 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. Note that the topics include both those
dealing directly with on-path network element collaboration and some
adjacent issues that would influence such collaboration.

* Some forms of collaboration may depend on business arrangements,
which may or may not be easy to put in place. For instance, some
quality-of-service mechanisms 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
proposition that is much harder for end-to-end connections across
multiple administrative domains [Claffy2015] [RFC9049].

* Secure communication with path elements is needed as discussed in
Section 2.3. Finding practical ways for this has been difficult,
both from the mechanics and scalability point of view, partially
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 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 network elements or endpoints.

* The use of path signals to reduce the effects of denial-of-service
attacks, e.g., perhaps modern forms of "source quench" designs,
could be developed. The difficulty is finding a solution that
would be both effective against attacks and would not enable third
parties from slowing down or censoring someone else's
communication.

* Work has begun on mechanisms that dissociate the information held
by servers from knowledge of the user's network location and
behavior. Among the solutions that exist for this but are not
widely deployed are [Oblivious] [PDoT] [DNS-CONFIDENTIAL]
[HTTP-OBLIVIOUS]. These solutions address specific parts of the
issue, and more work remains to find ways to limit the spread of
information about the user's actions. Host applications currently
share sensitive information about the user's action with a variety
of infrastructure and path elements, starting from basic data,
such as domain names, source and destination addresses, and
protocol header information. This can expand to detailed end-user
identity and other information learned by the servers. Work to
protect all of this information is needed.

* Work is needed to explore how to increase the deployment of
mechanisms for sharing information from networks to applications.
There are some working examples of this, e.g., ECN. A few other
proposals have been made (see, e.g.,
[MOBILE-THROUGHPUT-GUIDANCE]), but very few of those have seen
deployment.

* Additional work on sharing information from applications to
networks would also be valuable. There are a few working examples
of this (see Section 1). Numerous proposals have been made in
this space, but most of them have not progressed through standards
or been deployed for a variety of reasons [RFC9049]. However,
several current or recent proposals exist, such as
[NETWORK-TOKENS].

* Data privacy regimes generally deal with multiple issues, not just
whether or not some information is shared with another party. For
instance, there may be rules regarding how long information can be
stored or what purpose that information may be used for. Similar
issues may also be applicable to the kind of information sharing
discussed in this document.

* The present work has focused on the technical aspects of making
collaboration safe and mutually beneficial, but of course,
deployments need to take into account various regulatory and other
policy matters. These include privacy regulation, competitive
issues, network neutrality aspects, and so on.

4. IANA Considerations

This document has no IANA actions.

5. Security Considerations

This document has no security considerations.

6. Informative References

[Claffy2015]
Claffy, KC. 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, DOI 10.2139/ssrn.2587262, November
2015, <https://papers.ssrn.com/sol3/
papers.cfm?abstract_id=2587262>.

[DNS-CONFIDENTIAL]
Arkko, J. and J. Novotny, "Privacy Improvements for DNS
Resolution with Confidential Computing", Work in Progress,
Internet-Draft, draft-arkko-dns-confidential-02, 2 July
2021, <https://datatracker.ietf.org/doc/html/draft-arkko-
dns-confidential-02>.

[EXPLICIT-COOP]
Trammell, B., Ed., "Architectural Considerations for
Transport Evolution with Explicit Path Cooperation", Work
in Progress, Internet-Draft, draft-trammell-stackevo-
explicit-coop-00, 23 September 2015,
<https://datatracker.ietf.org/doc/html/draft-trammell-
stackevo-explicit-coop-00>.

[HTTP-OBLIVIOUS]
Thomson, M. and C. A. Wood, "Oblivious HTTP", Work in
Progress, Internet-Draft, draft-thomson-http-oblivious-02,
24 August 2021, <https://datatracker.ietf.org/doc/html/
draft-thomson-http-oblivious-02>.

[MOBILE-THROUGHPUT-GUIDANCE]
Jain, A., Terzis, A., Flinck, H., Sprecher, N.,
Arunachalam, S., Smith, K., Devarapalli, V., and R. Bar
Yanai, "Mobile Throughput Guidance Inband Signaling
Protocol", Work in Progress, Internet-Draft, draft-flinck-
mobile-throughput-guidance-04, 13 March 2017,
<https://datatracker.ietf.org/doc/html/draft-flinck-
mobile-throughput-guidance-04>.

[NETWORK-TOKENS]
Yiakoumis, Y., McKeown, N., and F. Sorensen, "Network
Tokens", Work in Progress, Internet-Draft, draft-
yiakoumis-network-tokens-02, 21 December 2020,
<https://datatracker.ietf.org/doc/html/draft-yiakoumis-
network-tokens-02>.

[Oblivious]
Schmitt, P., Edmundson, A., Mankin, A., and N. Feamster,
"Oblivious DNS: Practical Privacy for DNS Queries",
Proceedings on Privacy Enhancing Technologies, Volume
2019, Issue 2, pp. 228-244, DOI 10.2478/popets-2019-0028,
December 2018, <https://doi.org/10.2478/popets-2019-0028>.

[PATH-SIGNALS-INFO]
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://datatracker.ietf.org/doc/html/
draft-arkko-path-signals-information-00>.

[PDoT] Nakatsuka, Y., Paverd, A., and G. Tsudik, "PDoT: Private
DNS-over-TLS with TEE Support", Digital Threats: Research
and Practice, Volume 2, Issue 1, Article No. 3, pp. 1-22,
DOI 10.1145/3431171, February 2021,
<https://doi.org/10.1145/3431171>.

[PER-APP-NETWORKING]
Colitti, L. and T. Pauly, "Per-Application Networking
Considerations", Work in Progress, Internet-Draft, draft-
per-app-networking-considerations-00, 15 November 2020,
<https://datatracker.ietf.org/doc/html/draft-per-app-
networking-considerations-00>.

[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>.

[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.

[RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of
Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,
February 2014, <https://www.rfc-editor.org/info/rfc7129>.

[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>.

[RFC8890] Nottingham, M., "The Internet is for End Users", RFC 8890,
DOI 10.17487/RFC8890, August 2020,
<https://www.rfc-editor.org/info/rfc8890>.

[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>.

[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>.

[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/info/rfc9293>.

[RFC9312] Kühlewind, M. and B. Trammell, "Manageability of the QUIC
Transport Protocol", RFC 9312, DOI 10.17487/RFC9312,
September 2022, <https://www.rfc-editor.org/info/rfc9312>.

IAB Members at the Time of Approval

Internet Architecture Board members at the time this document was
approved for publication were:

Jari Arkko
Deborah Brungard
Lars Eggert
Wes Hardaker
Cullen Jennings
Mallory Knodel
Mirja Kühlewind
Zhenbin Li
Tommy Pauly
David Schinazi
Russ White
Qin Wu
Jiankang Yao

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 [PER-APP-NETWORKING] and
[PATH-SIGNALS-INFO]. We would also like to acknowledge that similar
thoughts are presented in [EXPLICIT-COOP]. Finally, the authors
would like to thank Adrian Farrell, Toerless Eckert, Martin Thomson,
Mark Nottingham, Luis M. Contreras, Watson Ladd, Vittorio Bertola,
Andrew Campling, Eliot Lear, Spencer Dawkins, Christian Huitema,
David Schinazi, Cullen Jennings, Mallory Knodel, Zhenbin Li, Chris
Box, and Jeffrey Haas for useful feedback on this topic and document.

Authors' Addresses

Jari Arkko
Ericsson
Email: [email protected]

Ted Hardie
Cisco
Email: [email protected]

Tommy Pauly
Apple
Email: [email protected]

Mirja Kühlewind
Ericsson
Email: [email protected]