Network Working Group                                           J. Arkko
Internet-Draft                                                  Ericsson
Intended status: Informational                                 T. Hardie
Expires: August 5, 2023                                            Cisco
                                                                T. Pauly
                                                           M. Kuehlewind
                                                       February 01, 2023

Considerations on Application - Network Collaboration Using Path Signals


   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 it is intended as a signal or not.  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 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

   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 August 5, 2023.

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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
   ( in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Principles  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Intentional Distribution  . . . . . . . . . . . . . . . .   7
     2.2.  Control of the Distribution of Information  . . . . . . .   7
     2.3.  Protecting Information and Authentication . . . . . . . .   8
     2.4.  Minimize Information  . . . . . . . . . . . . . . . . . .   9
     2.5.  Limiting Impact of Information  . . . . . . . . . . . . .  10
     2.6.  Minimum Set of Entities . . . . . . . . . . . . . . . . .  11
     2.7.  Carrying Information  . . . . . . . . . . . . . . . . . .  11
   3.  Further Work  . . . . . . . . . . . . . . . . . . . . . . . .  12
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  14
   5.  Informative References  . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   [RFC8558] defines the term "path signals" as signals to or from on-
   path elements.  Today path signals are often implicit, e.g. 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 [RFC0793] 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
   simply information that happens to be easily available is used

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   instead the information that would be 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 limits the evolvability of the
   protocols in question.

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

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

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

   o  Basing network behaviour on information that may be incomplete or

   o  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 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 and private communication that is only
   visible to a very limited set of parties, often one on each "end";
   and unauthenticated public communication that is also visible to all
   network elements on a path.

   Exposed information encourages pervasive monitoring, which is
   described in RFC 7258 [RFC7258], and 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 signalling, 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

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   As such, 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 the
   content being accessed, the user identity, or the application in use.
   Similarly, network congestion status information does not have to
   reveal network topology or 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 signalling, as recommended by RFC 8558

   For instance, QUIC replaces TCP for various applications and ensures
   end-to-end signals 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
   [I-D.ietf-quic-manageability].  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

   Another extreme is to employ explicit trust and coordination between
   specific entities, endpoints as well as 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:

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   o  To ensure that information is distributed intentionally, not

   o  to understand the privacy and other implications of any
      distributed information;

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

   o  to 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 functions
   should consider:

   o  Which entities must consent to the information exchange?

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

   o  What is the effect that new signals should have?

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

   o  What is the right mechanism and needed level of trust to convey
      this kind of information?

   If we look ways network 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.

   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.

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   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 recommended reading on this
   same general topic.  [RFC9049], an IRTF document, provides a
   catalogue 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 draft 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 some examples and explanation of
   situations that not following the principles can lead to.  Section 3
   points to topics that need more 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 signalling.

   While RFC 8558 [RFC8558] focused specifically on communication to
   "on-path elements", the principles described in this document apply
   potentially to

   o  on-path signalling, in either direction

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

   An example of on-path signalling is communication between an endpoint
   and a router on a network path.  An example of signalling 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
   from and to other parties, rather than creating a multiparty

   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

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   to ensuring that the use of path signals does not create a
   disproportionate opportunity for observers to extract new data from

2.1.  Intentional Distribution

   This 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

   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.  And that
   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, different applications, and different directions of
   communication influence the the analysis, and can lead to very
   different conclusions about what information can be shared or 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 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
   enabling each entity to have the highest posssible 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 adequate control to each entity over the collaboration
   or information sharing.  This can be achieved as discussed below.

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   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 signalling
   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 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 this.  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

   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 information shared 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 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 an 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,
   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 kind of interactions are also advisory in their nature
   (see also section Section 2.5).

   In other cases it may be necessary to establish a secure signalling
   channel for communication with a specific other party, e.g., between
   a network element and an application.  This channel may need to be

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   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 there's a danger of an attack where
   someone else may forge messages that could endanger the

   Authenticated integrity protections on signalled 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, information sent about users, or information sent by
   the network.  This also applies to any information related to flow

   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 mitigation technique to protect privacy and provides
   further guidance.

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   In looking at what information can or cannot easily be passed, we
   need to consider 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 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

   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.

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 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 to be advisory
   information, with the effect of optimizing or adjusting the behavior
   of connections on a specific path.  In the case of a firewall

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   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

   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 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.

2.7.  Carrying Information

   There is a distinction between what information is sent and how it is
   sent.  The actually sent information may be limited, while the
   mechanisms for sending or requesting information can be capable of
   sharing 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, such as
   making it mandatory to identify specific applications or users.  This
   is undesirable.

   This document recommends that signalling mechanisms that send
   information are 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

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   itself, and as such provisioning of flow identifiers also requires
   protocol specific analysis.

   Further, such mechanisms also need have an ability for establishing
   an agreement (see Section 2.2) and to establish 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
   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.
   But 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, is not a
   privacy concern, and 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, as
   well as some adjacent issues that would influence such collaboration.

   o  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
      much harder proposition for end-to-end connections across multiple
      administrative domains [Claffy2015] [RFC9049].

   o  Secure communications 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 view.  And 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 information (such as
      ECN bits) that is distributed openly within a path, but there are

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      limited examples of designs with secure information exchange with
      specific network elements or endpoints.

   o  The use of path signals for reducing 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

   o  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 parties, 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.

   o  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., [I-D.flinck-mobile-throughput-guidance]),
      but very few of those have seen deployment.

   o  Sharing information from applications to networks.  There are a
      few more working examples of this (see Section 1).  However,
      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].  Several current or recent proposals
      exist, however, such as [I-D.yiakoumis-network-tokens].

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

   o  The present work has focused on the technical aspects of making
      collabration 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.

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4.  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, 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 this draft.

5.  Informative References

              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.

              Arkko, J. and J. Novotny, "Privacy Improvements for DNS
              Resolution with Confidential Computing", draft-arkko-dns-
              confidential-02 (work in progress), July 2021,

              Arkko, J., "Considerations on Information Passed between
              Networks and Applications", draft-arkko-path-signals-
              information-00 (work in progress), February 2021,

              Jain, A., Terzis, A., Flinck, H., Sprecher, N.,
              Arunachalam, S., Smith, K., Devarapalli, V., and R. Yanai,
              "Mobile Throughput Guidance Inband Signaling Protocol",
              draft-flinck-mobile-throughput-guidance-04 (work in
              progress), March 2017, <

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              Kuehlewind, M. and B. Trammell, "Manageability of the QUIC
              Transport Protocol", draft-ietf-quic-manageability-18
              (work in progress), July 2022,

              Colitti, L. and T. Pauly, "Per-Application Networking
              Considerations", draft-per-app-networking-
              considerations-00 (work in progress), November 2020,

              Thomson, M. and C. Wood, "Oblivious HTTP", draft-thomson-
              http-oblivious-02 (work in progress), August 2021,

              Trammell, B., "Architectural Considerations for Transport
              Evolution with Explicit Path Cooperation", draft-trammell-
              stackevo-explicit-coop-00 (work in progress), September
              2015, <

              Yiakoumis, Y., McKeown, N., and F. Sorensen, "Network
              Tokens", draft-yiakoumis-network-tokens-02 (work in
              progress), December 2020,

              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,
              fullHtml/10.1145/3431171 , February 2021.

   [RFC0793]  Postel, J., "Transmission Control Protocol", RFC 793,
              DOI 10.17487/RFC0793, September 1981, <https://www.rfc-

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   [RFC5218]  Thaler, D. and B. Aboba, "What Makes for a Successful
              Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,

   [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-

   [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-

   [RFC7129]  Gieben, R. and W. Mekking, "Authenticated Denial of
              Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,
              February 2014, <>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <>.

   [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-

   [RFC8558]  Hardie, T., Ed., "Transport Protocol Path Signals",
              RFC 8558, DOI 10.17487/RFC8558, April 2019,

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

   [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-

   [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-

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   [RFC9075]  Arkko, J., Farrell, S., Kuehlewind, M., and C. Perkins,
              "Report from the IAB COVID-19 Network Impacts Workshop
              2020", RFC 9075, DOI 10.17487/RFC9075, July 2021,

Authors' Addresses

   Jari Arkko


   Ted Hardie


   Tommy Pauly


   Mirja Kuehlewind


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