< draft-irtf-panrg-questions-07.txt   draft-irtf-panrg-questions-10.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 August 29, 2020 Intended status: Informational 11 October 2021
Expires: March 2, 2021 Expires: 14 April 2022
Current Open Questions in Path Aware Networking Current Open Questions in Path Aware Networking
draft-irtf-panrg-questions-07 draft-irtf-panrg-questions-10
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. This document poses paths through the Internet for their traffic. While this property of
questions in path-aware networking open as of 2020, that must be "path awareness" already exists in many Internet-connected networks
answered in the design, development, and deployment of path-aware within single domains and via administrative interfaces to the
internetworks. It was originally written to frame discussions in the network layer, a fully path-aware internetwork expands these concepts
Path Aware Networking proposed Research Group (PANRG), and has been across layers and across the Internet.
published to snapshot current thinking in this space.
This document poses questions in path-aware networking open as of
2021, that must be answered in the design, development, and
deployment of path-aware internetworks. It was originally written to
frame discussions in the Path Aware Networking proposed Research
Group (PANRG), and has been published to snapshot current thinking in
this space.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/panrg/questions.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 2, 2021. This Internet-Draft will expire on 14 April 2022.
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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 . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 4
2. Questions . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Questions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. A Vocabulary of Path Properties . . . . . . . . . . . . . 4 2.1. A Vocabulary of Path Properties . . . . . . . . . . . . . 4
2.2. Discovery, Distribution, and Trustworthiness of Path 2.2. Discovery, Distribution, and Trustworthiness of Path
Properties . . . . . . . . . . . . . . . . . . . . . . . 4 Properties . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Supporting Path Selection . . . . . . . . . . . . . . . . 5 2.3. Supporting Path Selection . . . . . . . . . . . . . . . . 6
2.4. Interfaces for Path Awareness . . . . . . . . . . . . . . 5 2.4. Interfaces for Path Awareness . . . . . . . . . . . . . . 6
2.5. Implications of Path Awareness for the Data Plane . . . . 6 2.5. Implications of Path Awareness for the Transport and
2.6. What is an Endpoint? . . . . . . . . . . . . . . . . . . 6 Application Layers . . . . . . . . . . . . . . . . . . . 7
2.7. Operating a Path Aware Network . . . . . . . . . . . . . 7 2.6. What is an Endpoint? . . . . . . . . . . . . . . . . . . 7
2.8. Deploying a Path Aware Network . . . . . . . . . . . . . 7 2.7. Operating a Path Aware Network . . . . . . . . . . . . . 8
3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 2.8. Deploying a Path Aware Network . . . . . . . . . . . . . 8
4. Informative References . . . . . . . . . . . . . . . . . . . 8 3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Informative References . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
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: an application can assume that a unverifiable, best-effort service to the endpoints using it. While
packet with a given destination address will eventually be forwarded there are technologies that attempt better-than-best-effort delivery,
toward that destination, but little else. A transport layer protocol the interfaces to these are generally administrative as opposed to
such as TCP can provide reliability over this best-effort service, endpoint-exposed (e.g. PCE [RFC4655] and SD-WAN approaches), and
and a protocol above the network layer such as IPsec AH [RFC4302] or they are often restricted to single administrative domains. In this
TLS [RFC8446] can authenticate the remote endpoint. However, little, environment, an application can assume that a packet with a given
if any, explicit information about the path is available, and destination address will eventually be forwarded toward that
assumptions about that path often do not hold, sometimes with serious destination, but little else.
impacts on the application, as in the case with BGP hijacking
attacks. 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 [RFC8446] can authenticate the remote
endpoint. However, little, if any, explicit information about the
path is available to the endpoint, and assumptions about that path
often do 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, and 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 vice versa, to those endpoints and the one endpoint to another, and to those endpoints and the applications
applications running on them, so that they can make this selection. running on them, so that they can make this selection. The ALTO
protocol [RFC7285] can be seen as an example of a path-awareness
approach implemented in transport-layer terms on the present Internet
protocol stack.
Path selection provides transparency and control to applications and Path selection provides explicit visibility and control of network
users of the network. Selection may be made at either the treatment to applications and users of the network. This selection
application layer or the transport layer. Path control at the packet is available to the application, transport, and/or network layer
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
traffic should traverse, for instance to confound passive traffic should traverse, for instance to confound passive
surveillance in the network core [RFC7624]. surveillance in the network core [RFC7624].
We note that this property of "path awareness" already exists in many We note that this property of "path awareness" already exists in many
Internet-connected networks within single domains. Indeed, much of Internet-connected networks within single domains. Indeed, much of
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This document presents a snapshot of open questions in this space This document presents a snapshot of open questions in this space
that will need to be answered in order to realize a path-aware that will need to be answered in order to realize a path-aware
internetworking architecture; it is published to further frame internetworking architecture; it is published to further frame
discussions within and outside the Path Aware Networking Research discussions within and outside the Path Aware Networking Research
Group, and is published with the rough consensus of that group. Group, and is published with the rough consensus of that group.
1.1. Definition 1.1. Definition
For purposes of this document, "path aware networking" describes For purposes of this document, "path aware networking" describes
endpoint discovery of the properties of paths they use for endpoint discovery of the properties of paths they use for
communication, and endpoint reaction to these properties that affects communication across an internetwork, and endpoint reaction to these
routing and/or transmission; note that this can and already does properties that affects routing and/or data transfer. Note that this
happen to some extent in the current Internet architecture. can and already does happen to some extent in the current Internet
architecture; this definition expands current techniques of path
discovery and manipulation to cross administrative domain boundaries
and up to the transport and application layers at the endpoints.
Expanding on this definition, a "path aware internetwork" is one in Expanding on this definition, a "path aware internetwork" is one in
which endpoint discovery of path properties and endpoint selection of which endpoint discovery of path properties and endpoint selection of
paths used by traffic exchanged by the endpoint are explicitly paths used by traffic exchanged by the endpoint are explicitly
supported, regardless of the specific design of the protocol features supported, regardless of the specific design of the protocol features
which enable this discovery and selection. which enable this discovery and selection.
A "path", for the purposes of these definitions, is abstractly
defined as a sequence of adjacent path elements over which a packet
can be transmitted, where the definition of "path element" is
technology-dependent. As this document is intended to pose questions
rather than answer them, it assumes that this definition will be
refined as part of the answer the first two questions it poses, about
the vocabulary of path properties and how they are disseminated.
Research into path aware networking covers any and all aspects of Research into path aware networking covers any and all aspects of
designing, building, and operating path aware internetworks or the designing, building, and operating path aware internetworks or the
networks and endpoints attached to them. This document presents a networks and endpoints attached to them. This document presents a
collection of research questions to address in order to make a path collection of research questions to address in order to make a path
aware Internet a reality. aware Internet a reality.
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
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The first question: how are paths and path properties defined and The first question: how are paths and path properties defined and
represented? represented?
2.2. Discovery, Distribution, and Trustworthiness of Path Properties 2.2. Discovery, Distribution, and Trustworthiness of 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 The second question: how do endpoints and applications get access to
trustworthy path properties? accurate, useful, and trustworthy path properties?
2.3. Supporting Path Selection 2.3. Supporting Path Selection
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
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
address, network layer address, higher-layer identifier or name, and
so on). In this case, care must be taken to present semantically
useful information to those making decisions about which path(s) to
trust.
The third question: how can endpoints select paths to use for traffic 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 in a way that can be trusted by the network, the endpoints, and the
applications using them? applications using them?
2.4. Interfaces for Path Awareness 2.4. Interfaces for 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 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 to the transport and The fourth question: how can interfaces among the network, transport,
application layers support the use of path awareness? and application layers support the use of path awareness?
2.5. Implications of Path Awareness for the Data Plane 2.5. Implications of Path Awareness for the Transport and Application
Layers
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
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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 The seventh question: how can a path aware network in a path aware
internetwork be effectively operated, given control inputs from the internetwork be effectively operated, given control inputs from
network administrator as well as from the endpoints? network administrators, application designers, and end users?
2.8. Deploying a Path Aware Network 2.8. Deploying a Path Aware Network
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 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
endpoint-driven control inputs. endpoint-driven control inputs.
Here the question of apparent versus actual conflicts of intent Here the question of apparent versus actual conflicts of intent
arises again: certain network operations requirements may appear arises again: certain network operations requirements may appear
essential, but are merely accidents of the interfaces provided by essential, but are merely accidents of the interfaces provided by
current routing and management protocols. Incentives for deployment current routing and management protocols. For example, related (but
must show how existing network operations requirements are met adjacent) to path aware networking, the widespread use of the TCP
through new path selection and property dissemination mechanisms. wire image [RFC8546] in network monitoring for DDoS prevention
appears in conflict with the deployment of encrypted transports, only
because path signaling [RFC8558] has been implicit in the deployment
of past transport protocols.
Similarly, incentives for deployment must show how existing network
operations requirements are met through new path selection and
property dissemination mechanisms.
The incentives for network operators and equipment vendors need to be The incentives for network operators and equipment vendors need to be
made clear, in terms of a plan to transition [RFC8170] an made clear, in terms of a plan to transition [RFC8170] an
internetwork to path-aware operation, one network and facility at a internetwork to path-aware operation, one network and facility at a
time. This plan to transition must also take into account that the time. This plan to transition must also take into account that the
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
explicitly radiates more information about the network's deployment
and configuration, and implicitly radiates information about endpoint
configuration and preference through path selection, must also be
addressed.
The eighth question: how can the incentives of network operators and The eighth question: how can the incentives of network operators and
end-users be aligned to realize the vision of path aware networking, end-users be aligned to realize the vision of path aware networking,
and how can the transition from current ("path-oblivious") to path- and how can the transition from current ("path-oblivious") to path-
aware networking be managed? 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, and Theresa Enghardt for discussions leading to Spencer Dawkins, Theresa Enghardt, and Laurent Ciavaglia, for
questions in this document, and for feedback on the document itself. discussions leading to questions in this document, and 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,
DOI 10.17487/RFC4302, December 2005, DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>. <https://www.rfc-editor.org/rfc/rfc4302>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/rfc/rfc4655>.
[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, DOI 10.17487/RFC7285, September 2014,
<https://www.rfc-editor.org/rfc/rfc7285>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann, Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A "Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624, Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015, DOI 10.17487/RFC7624, August 2015,
<https://www.rfc-editor.org/info/rfc7624>. <https://www.rfc-editor.org/rfc/rfc7624>.
[RFC8170] Thaler, D., Ed., "Planning for Protocol Adoption and [RFC8170] Thaler, D., Ed., "Planning for Protocol Adoption and
Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170, Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170,
May 2017, <https://www.rfc-editor.org/info/rfc8170>. May 2017, <https://www.rfc-editor.org/rfc/rfc8170>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/rfc/rfc8446>.
[RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
2019, <https://www.rfc-editor.org/rfc/rfc8546>.
[RFC8558] Hardie, T., Ed., "Transport Protocol Path Signals",
RFC 8558, DOI 10.17487/RFC8558, April 2019,
<https://www.rfc-editor.org/rfc/rfc8558>.
Author's Address Author's Address
Brian Trammell Brian Trammell
Google Switzerland GmbH Google Switzerland GmbH
Gustav-Gull-Platz 1 Gustav-Gull-Platz 1
8004 Zurich CH- 8004 Zurich
Switzerland Switzerland
Email: ietf@trammell.ch Email: ietf@trammell.ch
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