Internet DRAFT - draft-trammell-panrg-questions
draft-trammell-panrg-questions
Path Aware Networking RG B. Trammell
Internet-Draft ETH Zurich
Intended status: Informational December 07, 2017
Expires: June 10, 2018
Open Questions in Path Aware Networking
draft-trammell-panrg-questions-02
Abstract
This document poses open questions in path-aware networking, as a
background for framing discussions in the Path Aware Networking
proposed Research Group (PANRG). These are split into making
properties of Internet paths available to endpoints, and allowing
endpoints to select paths through the Internet for their traffic.
Status of This Memo
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Table of Contents
1. Introduction to Path-Aware Networking . . . . . . . . . . . . 2
2. Questions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. A Vocabulary of Path Properties . . . . . . . . . . . . . 3
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. Implications of Path Awareness for the Data Plane . . . . 4
2.6. What is an Endpoint? . . . . . . . . . . . . . . . . . . 5
2.7. Operating a Path Aware Network . . . . . . . . . . . . . 5
2.8. Deploying a Path Aware Network . . . . . . . . . . . . . 6
3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
4. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Normative References . . . . . . . . . . . . . . . . . . 6
4.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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 across maximally-disjoing paths
through the Internet, even over a single interface. It also provides
transparency and control for applications and end-users to specify
constraints on the paths its traffic should traverse, for instance to
confound pervasive passive surveillance in the network core.
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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
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
represented?
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
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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
properties?
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
tradeoff.
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. Implications of Path Awareness for the Data Plane
In the current Internet, the basic assumption that at a given time t
all traffic for a given flow will traverse a single path, for some
definition of path, generally holds. In a path aware network, this
assumption no longer holds. The failure of this assumption has
implications for the design of protocols above a path-aware network
layer.
For example, one advantage of multipath communication is that a given
end-to-end flow can be "sprayed" along multiple paths in order to
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confound attempts to collect data or metadata from those flows for
pervasive surveillance purposes [RFC7624]. However, the benefits of
this approach are reduced if the upper-layer protocols use linkable
identifiers on packets belonging to the same flow across different
paths. Clients may mitigate linkability by opting to not re-use
cleartext connection identifiers, such as TLS session IDs or tickets,
on separate paths. The privacy-conscious strategies required for
effective privacy in a path-aware Internet are only possible if
higher-layer protocols such as TLS permit clients to obtain
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?
The vision of path-aware networking articulated so far makes an
assumption that path properties will be disseminated to endpoints on
which applications are running (terminals with user agents, servers,
and so on). However, incremental deployment may require that a path-
aware network "core" be used to interconnect islands of legacy
protocol networks. In these cases, it is the gateways, not the
application endpoints, that receive path properties and make path
selections for that traffic. The interfaces provided this gateway
are necessarily different than those a path-aware networking layer
provides to its transport and application layers, and the path
property information the gateway needs and makes available over those
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
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.
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The seventh question: how can a path aware network in a path aware
internetwork be effectively operated, given control inputs from the
network administrator as well as from the endpoints?
2.8. Deploying a Path Aware Network
The vision presented in the introduction discusses path aware
networking from the point of view of the benefits accruing at the
endpoints, to designers of transport protocols and applications as
well as to the end users of those applications. However, this vision
requires action not only at the endpoints but within the
interconnected networks offering path aware connectivity. While the
specific actions required are a matter of the design and
implementation of a specific realization of a path aware protocol
stack, it is clear than any path aware architecture will require
network operators to give up some control of their networks over to
endpoint-driven control inputs. The incentives for network operators
and equipment vendors to do this must be made clear.
The eighth question: how can the incentives of network operators and
end-users be aligned to realize the vision of path aware networking?
3. Acknowledgments
Many thanks to Adrian Perrig, Jean-Pierre Smith, Mirja Kuehlewind,
Olivier Bonaventure, Martin Thomson, Shwetha Bhandari, and Chris
Wood, for discussions leading to questions in this document.
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. References
4.1. Normative References
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
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4.2. Informative References
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015,
<https://www.rfc-editor.org/info/rfc7624>.
Author's Address
Brian Trammell
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: ietf@trammell.ch
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