Path Aware Networking RG                                     B. Trammell
Internet-Draft                                                ETH Zurich
Intended status: Informational                          October 24, 2017
Expires: April 27, 2018

                Open Questions in Path Aware Networking


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Table of Contents

   1.  Introduction to Path-Aware Networking . . . . . . . . . . . .   2
   2.  Questions . . . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  A Vocabulary of Path Properties . . . . . . . . . . . . .   2
     2.2.  Discovery, Distribution, and Trustworthiness of Path
           Properties  . . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Supporting Path Selection . . . . . . . . . . . . . . . .   4
     2.4.  Interfaces for Path Awareness . . . . . . . . . . . . . .   4
     2.5.  Operating a Path Aware Network  . . . . . . . . . . . . .   4
   3.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction to Path-Aware Networking

   In the current Internet architecture, the network layer provides an
   unverifiable, best-effort service: an application can assume that a
   packet with a given destination address will eventually be forwarded
   toward that destination, but little else.  A transport layer protocol
   such as TCP can provide reliability over this best-effort service,
   and a protocol above the network layer such as IPsec AH [RFC4302] or
   TLS [RFC5246] can authenticate the remote endpoint.  However, no
   explicit information about the path is available, and assumptions
   about that path sometimes do not hold, sometimes with serious impacts
   on the application, as in the case with BGP hijacking attacks.

   By contrast, in a path-aware networking architecture, endpoints have
   the ability to select or influence the path through the network used
   by any given packet, and the network layer explicitly exposes
   information about the path or paths available between two endpoints
   to those endpoints so that they can make this selection.  Path
   control at the packet level enables new transport protocols that can
   leverage multipath connectivity even over a single interface.

2.  Questions

   Realizing path-aware networking requires answers to a set of open
   research questions.  This document poses these questions, as a
   starting point for discussions about how to realize path awareness in
   the Internet, and to direct future research efforts within the Path
   Aware Networking Research Group.

2.1.  A Vocabulary of Path Properties

   In order for information about paths to be exposed to the endpoints,
   and for those endpoints to be able to use that information, it is
   necessary to define a common vocabulary for path properties.  The

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   elements of this vocabulary could include relatively static
   properties, such as the presence of a given node on the path; as well
   as relatively dynamic properties, such as the current values of
   metrics such as loss and latency.

   This vocabulary must be defined carefully, as its design will have
   impacts on the expressiveness of a given path-aware internetworking
   architecture.  This expressiveness also exhibits tradeoffs.  For
   example, a system that exposes node-level information for the
   topology through each network would maximize information about the
   individual components of the path at the endpoints at the expense of
   making internal network topology universally public, which may be in
   conflict with the business goals of each network's operator.

   The first question is therefore: how are path properties defined and

2.2.  Discovery, Distribution, and Trustworthiness of Path Properties

   Once endpoints and networks have a shared vocabulary for expressing
   path properties, the network must have some method for distributing
   those path properties to the endpoint.  Regardless of how path
   property information is distributed to the endpoints, the endpoints
   require a method to authenticate the properties - to determine that
   they originated from and pertain to the path that they purport to.
   The end goal of authentication is not necessarily to establish that a
   given property is actually bound to a given path, but to ensure that
   the information is trustworthy, that actions taken based on it will
   have the predicted result.

   Choices in an distribution and authentication methods will have
   impacts on the scalability of a path-aware architecture.  Possible
   dimensions in the space of distribution methods include in-band
   versus out-of-band, push versus pull versus publish-subscribe, and so
   on.  There are temporal issues with path property dissemination as
   well, especially with dynamic properties, since the measurement or
   elicitation of dynamic properties may be outdated by the time that
   information is available at the endpoints, and interactions between
   the measurement and dissemination delay may exhibit pathological
   behavior for unlucky points in the parameter space.

   The second question: how do endpoints get access to trustworthy path

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2.3.  Supporting Path Selection

   Access to trustworthy path properties is only half of the challenge
   in establishing a path-aware architecture.  Endpoints must be able to
   use this information in order to select paths for traffic they send.
   As with path property distribution, choices made in path selection
   methods will also have an impact on the scalability and
   expressiveness of a path-aware architecture, and dimensions included
   in-band versus out-of-band, as well.  Paths may also be selected on
   multiple levels of granularity - per packet, per flow, per aggregate
   - and this choice also has impacts on the scalabilty/expressiveness

   The third question: how can endpoints select paths to use for traffic
   in a way that can be trusted by the network?

2.4.  Interfaces for Path Awareness

   In order for applications to make effective use of a path-aware
   networking architecture, the interfaces presented by the network and
   transport layers must also expose path properties to the application
   in a useful way, and provide a useful selection for path selection.
   Path selection must be possible based not only on the preferences and
   policies of the application developer, but of end-users as well.

   The fourth question: how can interfaces to the transport and
   application layers support the use of path awareness?

2.5.  Operating a Path Aware Network

   The network operations model in the current Internet architecture
   assumes that traffic flows are controlled by the decisions and
   policies made by network operators, as expressed in interdomain
   routing protocols.  In a path-aware network with effective path
   selection, however, this assumption no longer holds, as endpoints may
   react to path properties by selecting alternate paths.  Competing
   control inputs from path-aware endpoints and the interdomain routing
   control plane may lead to more difficult traffic engineering or
   nonconvergent routing, especially if the endpoints' and operators'
   idea of the "best" path for given traffic differs significantly.

   The fifth question: how can a path aware network in a path aware
   internetwork be effectively operated?

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3.  Acknowledgments

   Many thanks to Adrian Perrig, Jean-Pierre Smith, Mirja Kuehlewind,
   and Olivier Bonaventure, for discussions leading to questions in this

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement no. 688421 Measurement and Architecture
   for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
   for Education, Research, and Innovation under contract no. 15.0268.
   This support does not imply endorsement.

4.  Normative References

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,

Author's Address

   Brian Trammell
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


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