< draft-irtf-panrg-questions-10.txt   draft-irtf-panrg-questions-11.txt >
Path Aware Networking RG B. Trammell Path Aware Networking RG B. Trammell
Internet-Draft Google Switzerland GmbH Internet-Draft Google Switzerland GmbH
Intended status: Informational 11 October 2021 Intended status: Informational 11 November 2021
Expires: 14 April 2022 Expires: 15 May 2022
Current Open Questions in Path Aware Networking Current Open Questions in Path Aware Networking
draft-irtf-panrg-questions-10 draft-irtf-panrg-questions-11
Abstract Abstract
In contrast to the present Internet architecture, a path-aware In contrast to the present Internet architecture, a path-aware
internetworking architecture has two important properties: it exposes internetworking architecture has two important properties: it exposes
the properties of available Internet paths to endpoints, and provides the properties of available Internet paths to endpoints, and provides
for endpoints and applications to use these properties to select for endpoints and applications to use these properties to select
paths through the Internet for their traffic. While this property of paths through the Internet for their traffic. While this property of
"path awareness" already exists in many Internet-connected networks "path awareness" already exists in many Internet-connected networks
within single domains and via administrative interfaces to the within single domains and via administrative interfaces to the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 April 2022. This Internet-Draft will expire on 15 May 2022.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction to Path-Aware Networking . . . . . . . . . . . . 2 1. Introduction to Path-Aware Networking . . . . . . . . . . . . 2
1.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 4
2. Questions . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Questions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. A Vocabulary of Path Properties . . . . . . . . . . . . . 4 2.1. A Vocabulary of Path Properties . . . . . . . . . . . . . 5
2.2. Discovery, Distribution, and Trustworthiness of Path 2.2. Discovery, Distribution, and Trustworthiness of Path
Properties . . . . . . . . . . . . . . . . . . . . . . . 5 Properties . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Supporting Path Selection . . . . . . . . . . . . . . . . 6 2.3. Supporting Path Selection . . . . . . . . . . . . . . . . 6
2.4. Interfaces for Path Awareness . . . . . . . . . . . . . . 6 2.4. Interfaces for Path Awareness . . . . . . . . . . . . . . 6
2.5. Implications of Path Awareness for the Transport and 2.5. Implications of Path Awareness for the Transport and
Application Layers . . . . . . . . . . . . . . . . . . . 7 Application Layers . . . . . . . . . . . . . . . . . . . 7
2.6. What is an Endpoint? . . . . . . . . . . . . . . . . . . 7 2.6. What is an Endpoint? . . . . . . . . . . . . . . . . . . 7
2.7. Operating a Path Aware Network . . . . . . . . . . . . . 8 2.7. Operating a Path Aware Network . . . . . . . . . . . . . 8
2.8. Deploying a Path Aware Network . . . . . . . . . . . . . 8 2.8. Deploying a Path Aware Network . . . . . . . . . . . . . 9
3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
4. Informative References . . . . . . . . . . . . . . . . . . . 9 4. Informative References . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction to Path-Aware Networking 1. Introduction to Path-Aware Networking
In the current Internet architecture, the network layer provides an In the current Internet architecture, the network layer provides an
unverifiable, best-effort service to the endpoints using it. While unverifiable, best-effort service to the endpoints using it. While
there are technologies that attempt better-than-best-effort delivery, there are technologies that attempt better-than-best-effort delivery,
the interfaces to these are generally administrative as opposed to the interfaces to these are generally administrative as opposed to
endpoint-exposed (e.g. PCE [RFC4655] and SD-WAN approaches), and endpoint-exposed (e.g. Path Computation Element (PCE) [RFC4655] and
they are often restricted to single administrative domains. In this Software-Defined Wide Area Network (SD-WAN) approaches), and they are
often restricted to single administrative domains. In this
environment, an application can assume that a packet with a given environment, an application can assume that a packet with a given
destination address will eventually be forwarded toward that destination address will eventually be forwarded toward that
destination, but little else. destination, but little else.
A transport layer protocol such as TCP can provide reliability over A transport layer protocol such as TCP can provide reliability over
this best-effort service, and a protocol above the network layer such this best-effort service, and a protocol above the network layer such
as IPsec AH [RFC4302] or TLS [RFC8446] can authenticate the remote as IPsec Authentication Header (AH) [RFC4302] or Transport Layer
endpoint. However, little, if any, explicit information about the Security (TLS) [RFC8446] can authenticate the remote endpoint.
path is available to the endpoint, and assumptions about that path However, little, if any, explicit information about the path is
often do not hold, sometimes with serious impacts on the application, available to the endpoint, and assumptions about that path often do
as in the case with BGP hijacking attacks. not hold, sometimes with serious impacts on the application, as in
the case with BGP hijacking attacks.
By contrast, in a path-aware internetworking architecture, endpoints By contrast, in a path-aware internetworking architecture, endpoints
have the ability to select or influence the path through the network have the ability to select or influence the path through the network
used by any given packet or flow. The network and transport layers used by any given packet or flow. The network and transport layers
explicitly expose information about the path or paths available from explicitly expose information about the path or paths available from
one endpoint to another, and to those endpoints and the applications one endpoint to another, and to those endpoints and the applications
running on them, so that they can make this selection. The ALTO running on them, so that they can make this selection. The
protocol [RFC7285] can be seen as an example of a path-awareness Application Layer Traffic Optimization (ALTO) protocol [RFC7285] can
approach implemented in transport-layer terms on the present Internet be seen as an example of a path-awareness approach implemented in
protocol stack. transport-layer terms on the present Internet protocol stack.
Path selection provides explicit visibility and control of network Path selection provides explicit visibility and control of network
treatment to applications and users of the network. This selection treatment to applications and users of the network. This selection
is available to the application, transport, and/or network layer is available to the application, transport, and/or network layer
entities at each endpoint. Path control at the flow and subflow entities at each endpoint. Path control at the flow and subflow
level enables the design of new transport protocols that can leverage level enables the design of new transport protocols that can leverage
multipath connectivity across disjoint paths through the Internet, multipath connectivity across disjoint paths through the Internet,
even over a single physical interface. When exposed to applications, even over a single physical interface. When exposed to applications,
or to end-users through a system configuration interface, path or to end-users through a system configuration interface, path
control allows the specification of constraints on the paths that control allows the specification of constraints on the paths that
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2. Questions 2. Questions
Realizing path-aware networking requires answers to a set of open Realizing path-aware networking requires answers to a set of open
research questions. This document poses these questions, as a research questions. This document poses these questions, as a
starting point for discussions about how to realize path awareness in starting point for discussions about how to realize path awareness in
the Internet, and to direct future research efforts within the Path the Internet, and to direct future research efforts within the Path
Aware Networking Research Group. Aware Networking Research Group.
2.1. A Vocabulary of Path Properties 2.1. A Vocabulary of Path Properties
The first question: how are paths and path properties defined and
represented?
In order for information about paths to be exposed to an endpoint, In order for information about paths to be exposed to an endpoint,
and for the endpoint to make use of that information, it is necessary and for the endpoint to make use of that information, it is necessary
to define a common vocabulary for paths through an internetwork, and to define a common vocabulary for paths through an internetwork, and
properties of those paths. The elements of this vocabulary could properties of those paths. The elements of this vocabulary could
include terminology for components of a path and properties defined include terminology for components of a path and properties defined
for these components, for the entire path, or for subpaths of a path. for these components, for the entire path, or for subpaths of a path.
These properties may be relatively static, such as the presence of a These properties may be relatively static, such as the presence of a
given node or service function on the path; as well as relatively given node or service function on the path; as well as relatively
dynamic, such as the current values of metrics such as loss and dynamic, such as the current values of metrics such as loss and
latency. latency.
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example, a system that exposes node-level information for the example, a system that exposes node-level information for the
topology through each network would maximize information about the topology through each network would maximize information about the
individual components of the path at the endpoints, at the expense of individual components of the path at the endpoints, at the expense of
making internal network topology universally public, which may be in making internal network topology universally public, which may be in
conflict with the business goals of each network's operator. conflict with the business goals of each network's operator.
Furthermore, properties related to individual components of the path Furthermore, properties related to individual components of the path
may change frequently and may quickly become outdated. However, may change frequently and may quickly become outdated. However,
aggregating the properties of individual components to distill end- aggregating the properties of individual components to distill end-
to-end properties for the entire path is not trivial. to-end properties for the entire path is not trivial.
The first question: how are paths and path properties defined and
represented?
2.2. Discovery, Distribution, and Trustworthiness of Path Properties 2.2. Discovery, Distribution, and Trustworthiness of Path Properties
The second question: how do endpoints and applications get access to
accurate, useful, and trustworthy path properties?
Once endpoints and networks have a shared vocabulary for expressing Once endpoints and networks have a shared vocabulary for expressing
path properties, the network must have some method for distributing path properties, the network must have some method for distributing
those path properties to the endpoint. Regardless of how path those path properties to the endpoint. Regardless of how path
property information is distributed to the endpoints, the endpoints property information is distributed to the endpoints, the endpoints
require a method to authenticate the properties -- to determine that require a method to authenticate the properties -- to determine that
they originated from and pertain to the path that they purport to. they originated from and pertain to the path that they purport to.
Choices in distribution and authentication methods will have impacts Choices in distribution and authentication methods will have impacts
on the scalability of a path-aware architecture. Possible dimensions on the scalability of a path-aware architecture. Possible dimensions
in the space of distribution methods include in-band versus out-of- in the space of distribution methods include in-band versus out-of-
band, push versus pull versus publish-subscribe, and so on. There band, push versus pull versus publish-subscribe, and so on. There
are temporal issues with path property dissemination as well, are temporal issues with path property dissemination as well,
especially with dynamic properties, since the measurement or especially with dynamic properties, since the measurement or
elicitation of dynamic properties may be outdated by the time that elicitation of dynamic properties may be outdated by the time that
information is available at the endpoints, and interactions between information is available at the endpoints, and interactions between
the measurement and dissemination delay may exhibit pathological the measurement and dissemination delay may exhibit pathological
behavior for unlucky points in the parameter space. behavior for unlucky points in the parameter space.
The second question: how do endpoints and applications get access to
accurate, useful, and trustworthy path properties?
2.3. Supporting Path Selection 2.3. Supporting Path Selection
The third question: how can endpoints select paths to use for traffic
in a way that can be trusted by the network, the endpoints, and the
applications using them?
Access to trustworthy path properties is only half of the challenge Access to trustworthy path properties is only half of the challenge
in establishing a path-aware architecture. Endpoints must be able to in establishing a path-aware architecture. Endpoints must be able to
use this information in order to select paths for specific traffic use this information in order to select paths for specific traffic
they send. As with the dissemination of path properties, choices they send. As with the dissemination of path properties, choices
made in path selection methods will also have an impact on the made in path selection methods will also have an impact on the
tradeoff between scalability and expressiveness of a path-aware tradeoff between scalability and expressiveness of a path-aware
architecture. One key choice here is between in-band and out-of-band architecture. One key choice here is between in-band and out-of-band
control of path selection. Another is granularity of path selection control of path selection. Another is granularity of path selection
(whether per packet, per flow, or per larger aggregate), which also (whether per packet, per flow, or per larger aggregate), which also
has a large impact on the scalabilty/expressiveness tradeoff. Path has a large impact on the scalabilty/expressiveness tradeoff. Path
selection must, like path property information, be trustworthy, such selection must, like path property information, be trustworthy, such
that the result of a path selection at an endpoint is predictable. that the result of a path selection at an endpoint is predictable.
Moreover, any path selection mechanism should aim to provide an Moreover, any path selection mechanism should aim to provide an
outcome that is not worse than using a single path, or selecting outcome that is not worse than using a single path, or selecting
paths at random. paths at random.
Path selection may be exposed in terms of the properties of the path Path selection may be exposed in terms of the properties of the path
or the identity of elements of the path. In the latter case, a path or the identity of elements of the path. In the latter case, a path
may be identified at any of multiple layers (e.g. control plane may be identified at any of multiple layers (e.g. routing domain
address, network layer address, higher-layer identifier or name, and identifier, network layer address, higher-layer identifier or name,
so on). In this case, care must be taken to present semantically and so on). In this case, care must be taken to present semantically
useful information to those making decisions about which path(s) to useful information to those making decisions about which path(s) to
trust. trust.
The third question: how can endpoints select paths to use for traffic
in a way that can be trusted by the network, the endpoints, and the
applications using them?
2.4. Interfaces for Path Awareness 2.4. Interfaces for Path Awareness
The fourth question: how can interfaces among the network, transport,
and application layers support the use of path awareness?
In order for applications to make effective use of a path-aware In order for applications to make effective use of a path-aware
networking architecture, the control interfaces presented by the networking architecture, the control interfaces presented by the
network and transport layers must also expose path properties to the network and transport layers must also expose path properties to the
application in a useful way, and provide a useful set of paths among application in a useful way, and provide a useful set of paths among
which the application can select. Path selection must be possible which the application can select. Path selection must be possible
based not only on the preferences and policies of the application based not only on the preferences and policies of the application
developer, but of end-users as well. Also, the path selection developer, but of end-users as well. Also, the path selection
interfaces presented to applications and end users will need to interfaces presented to applications and end users will need to
support multiple levels of granularity. Most applications' support multiple levels of granularity. Most applications'
requirements can be satisfied with the expression of path selection requirements can be satisfied with the expression of path selection
policies in terms of properties of the paths, while some applications policies in terms of properties of the paths, while some applications
may need finer-grained, per-path control. These interfaces will need may need finer-grained, per-path control. These interfaces will need
to support incremental development and deployment of applications, to support incremental development and deployment of applications,
and provide sensible defaults, to avoid hindering their adoption. and provide sensible defaults, to avoid hindering their adoption.
The fourth question: how can interfaces among the network, transport,
and application layers support the use of path awareness?
2.5. Implications of Path Awareness for the Transport and Application 2.5. Implications of Path Awareness for the Transport and Application
Layers Layers
The fifth question: how should transport-layer and higher layer
protocols be redesigned to work most effectively over a path-aware
networking layer?
In the current Internet, the basic assumption that at a given time In the current Internet, the basic assumption that at a given time
all traffic for a given flow will receive the same network treatment all traffic for a given flow will receive the same network treatment
and traverse the same path or equivalend paths often holds. In a and traverse the same path or equivalend paths often holds. In a
path aware network, this assumption is more easily violated. The path aware network, this assumption is more easily violated. The
weakening of this assumption has implications for the design of weakening of this assumption has implications for the design of
protocols above any path-aware network layer. protocols above any path-aware network layer.
For example, one advantage of multipath communication is that a given For example, one advantage of multipath communication is that a given
end-to-end flow can be "sprayed" along multiple paths in order to end-to-end flow can be "sprayed" along multiple paths in order to
confound attempts to collect data or metadata from those flows for confound attempts to collect data or metadata from those flows for
pervasive surveillance purposes [RFC7624]. However, the benefits of pervasive surveillance purposes [RFC7624]. However, the benefits of
this approach are reduced if the upper-layer protocols use linkable this approach are reduced if the upper-layer protocols use linkable
identifiers on packets belonging to the same flow across different identifiers on packets belonging to the same flow across different
paths. Clients may mitigate linkability by opting to not re-use paths. Clients may mitigate linkability by opting to not re-use
cleartext connection identifiers, such as TLS session IDs or tickets, cleartext connection identifiers, such as TLS session IDs or tickets,
on separate paths. The privacy-conscious strategies required for on separate paths. The privacy-conscious strategies required for
effective privacy in a path-aware Internet are only possible if effective privacy in a path-aware Internet are only possible if
higher-layer protocols such as TLS permit clients to obtain higher-layer protocols such as TLS permit clients to obtain
unlinkable identifiers. unlinkable identifiers.
The fifth question: how should transport-layer and higher layer
protocols be redesigned to work most effectively over a path-aware
networking layer?
2.6. What is an Endpoint? 2.6. What is an Endpoint?
The sixth question: how is path awareness (in terms of vocabulary and
interfaces) different when applied to tunnel and overlay endpoints?
The vision of path-aware networking articulated so far makes an The vision of path-aware networking articulated so far makes an
assumption that path properties will be disseminated to endpoints on assumption that path properties will be disseminated to endpoints on
which applications are running (terminals with user agents, servers, which applications are running (terminals with user agents, servers,
and so on). However, incremental deployment may require that a path- and so on). However, incremental deployment may require that a path-
aware network "core" be used to interconnect islands of legacy aware network "core" be used to interconnect islands of legacy
protocol networks. In these cases, it is the gateways, not the protocol networks. In these cases, it is the gateways, not the
application endpoints, that receive path properties and make path application endpoints, that receive path properties and make path
selections for that traffic. The interfaces provided by this gateway selections for that traffic. The interfaces provided by this gateway
are necessarily different than those a path-aware networking layer are necessarily different than those a path-aware networking layer
provides to its transport and application layers, and the path provides to its transport and application layers, and the path
property information the gateway needs and makes available over those property information the gateway needs and makes available over those
interfaces may also be different. interfaces may also be different.
The sixth question: how is path awareness (in terms of vocabulary and
interfaces) different when applied to tunnel and overlay endpoints?
2.7. Operating a Path Aware Network 2.7. Operating a Path Aware Network
The seventh question: how can a path aware network in a path aware
internetwork be effectively operated, given control inputs from
network administrators, application designers, and end users?
The network operations model in the current Internet architecture The network operations model in the current Internet architecture
assumes that traffic flows are controlled by the decisions and assumes that traffic flows are controlled by the decisions and
policies made by network operators, as expressed in interdomain and policies made by network operators, as expressed in interdomain and
intradomain routing protocols. In a network providing path selection intradomain routing protocols. In a network providing path selection
to the endpoints, however, this assumption no longer holds, as to the endpoints, however, this assumption no longer holds, as
endpoints may react to path properties by selecting alternate paths. endpoints may react to path properties by selecting alternate paths.
Competing control inputs from path-aware endpoints and the routing Competing control inputs from path-aware endpoints and the routing
control plane may lead to more difficult traffic engineering or control plane may lead to more difficult traffic engineering or
nonconvergent forwarding, especially if the endpoints' and operators' nonconvergent forwarding, especially if the endpoints' and operators'
notion of the "best" path for given traffic diverges significantly. notion of the "best" path for given traffic diverges significantly.
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A concept for path aware network operations will need to have clear A concept for path aware network operations will need to have clear
methods for the resolution of apparent (if not actual) conflicts of methods for the resolution of apparent (if not actual) conflicts of
intent between the network's operator and the path selection at an intent between the network's operator and the path selection at an
endpoint. It will also need set of safety principles to ensure that endpoint. It will also need set of safety principles to ensure that
increasing path control does not lead to decreasing connectivity; one increasing path control does not lead to decreasing connectivity; one
such safety principle could be "the existence of at least one path such safety principle could be "the existence of at least one path
between two endpoints guarantees the selection of at least one path between two endpoints guarantees the selection of at least one path
between those endpoints." between those endpoints."
The seventh question: how can a path aware network in a path aware
internetwork be effectively operated, given control inputs from
network administrators, application designers, and end users?
2.8. Deploying a Path Aware Network 2.8. Deploying a Path Aware Network
The eighth question: how can the incentives of network operators and
end-users be aligned to realize the vision of path aware networking,
and how can the transition from current ("path-oblivious") to path-
aware networking be managed?
The vision presented in the introduction discusses path aware The vision presented in the introduction discusses path aware
networking from the point of view of the benefits accruing at the networking from the point of view of the benefits accruing at the
endpoints, to designers of transport protocols and applications as endpoints, to designers of transport protocols and applications as
well as to the end users of those applications. However, this vision well as to the end users of those applications. However, this vision
requires action not only at the endpoints but also within the requires action not only at the endpoints but also within the
interconnected networks offering path aware connectivity. While the interconnected networks offering path aware connectivity. While the
specific actions required are a matter of the design and specific actions required are a matter of the design and
implementation of a specific realization of a path aware protocol implementation of a specific realization of a path aware protocol
stack, it is clear than any path aware architecture will require stack, it is clear than any path aware architecture will require
network operators to give up some control of their networks over to network operators to give up some control of their networks over to
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dynamics of path aware networking early in this transition (when few dynamics of path aware networking early in this transition (when few
endpoints and flows in the Internet use path selection) may be endpoints and flows in the Internet use path selection) may be
different than those later in the transition. different than those later in the transition.
Aspects of data security and information management in a network that Aspects of data security and information management in a network that
explicitly radiates more information about the network's deployment explicitly radiates more information about the network's deployment
and configuration, and implicitly radiates information about endpoint and configuration, and implicitly radiates information about endpoint
configuration and preference through path selection, must also be configuration and preference through path selection, must also be
addressed. addressed.
The eighth question: how can the incentives of network operators and
end-users be aligned to realize the vision of path aware networking,
and how can the transition from current ("path-oblivious") to path-
aware networking be managed?
3. Acknowledgments 3. Acknowledgments
Many thanks to Adrian Perrig, Jean-Pierre Smith, Mirja Kuehlewind, Many thanks to Adrian Perrig, Jean-Pierre Smith, Mirja Kuehlewind,
Olivier Bonaventure, Martin Thomson, Shwetha Bhandari, Chris Wood, Olivier Bonaventure, Martin Thomson, Shwetha Bhandari, Chris Wood,
Lee Howard, Mohamed Boucadair, Thorben Krueger, Gorry Fairhurst, Lee Howard, Mohamed Boucadair, Thorben Krueger, Gorry Fairhurst,
Spencer Dawkins, Theresa Enghardt, and Laurent Ciavaglia, for Spencer Dawkins, Theresa Enghardt, Laurent Ciavaglia, and Stephen
discussions leading to questions in this document, and for feedback Farrell, for discussions leading to questions in this document, and
on the document itself. for feedback on the document itself.
This work is partially supported by the European Commission under This work is partially supported by the European Commission under
Horizon 2020 grant agreement no. 688421 Measurement and Architecture Horizon 2020 grant agreement no. 688421 Measurement and Architecture
for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
for Education, Research, and Innovation under contract no. 15.0268. for Education, Research, and Innovation under contract no. 15.0268.
This support does not imply endorsement. This support does not imply endorsement.
4. Informative References 4. Informative References
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, [RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
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