Continuing to Evolve Internet Routing Beyond 'Mere' Reachability
draft-trossen-rtgwg-routing-beyond-reachability-00
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| Authors | Dirk Trossen , Zhe Lou , Sheng Jiang | ||
| Last updated | 2022-02-08 | ||
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draft-trossen-rtgwg-routing-beyond-reachability-00
Network Working Group D. Trossen
Internet-Draft D. Lou
Intended status: Informational S. Jiang
Expires: 12 August 2022 Huawei Technologies
8 February 2022
Continuing to Evolve Internet Routing Beyond 'Mere' Reachability
draft-trossen-rtgwg-routing-beyond-reachability-00
Abstract
This document discusses the evolution of the Internet routing system
beyond mere reachability. We observe, through examples of past
development, that such evolution has been taking place to improve on
capabilities of the Internet, deal with more complicated network
deployments and cater to changing requirements by end users as well
as novel and emerging applications.
For achieving a routing system that serves more than a singular
reachability purpose, more information is taken into account when
performing the purpose-specific functions. Such extra information
can be obtained by extending current routing protocols to exchange
more information or by carrying that information within packets.
This document is intended to seed discussions of how the observed
evolution of the Internet's routing system can continue, what issues
may occur when simply continuing the current approach for achieving
routing beyond 'mere' reachability and what may be needed to address
those issues. Ultimately, however, this document recognizes the
positive impact that moving beyond reachability has brought to the
Internet and will continue to do so.
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
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Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
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This Internet-Draft will expire on 12 August 2022.
Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Reachability - Original Purpose of the Routing System . . . . 4
3. Extension of the Routing System Beyond 'Mere' Reachability . 5
4. Issues with Current Approaches . . . . . . . . . . . . . . . 8
4.1. Limiting Routing Semantics . . . . . . . . . . . . . . . 8
4.2. Complexity and Efficiency . . . . . . . . . . . . . . . . 9
4.2.1. Repetitive encapsulation . . . . . . . . . . . . . . 9
4.2.2. Introducing Path Stretch . . . . . . . . . . . . . . 10
4.2.3. Complicating Traffic Engineering . . . . . . . . . . 10
4.3. Security . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4. Fragility . . . . . . . . . . . . . . . . . . . . . . . . 11
4.5. Interoperability . . . . . . . . . . . . . . . . . . . . 11
5. Where to Go From Here? . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14
11. Informative References . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
The current routing system was initially designed for a single
purpose - reachability. That is, it was built to find paths through
the network so as to forward packets to their destinations. The
routing system has successfully supported the Internet as it grew
from a very small scale network to a giant system that covers the
whole world with billions attached devices and users. This routing
system has done a good job for global reachability, however, through
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the years, many other needs or purposes have arisen in the Internet,
such as hostname/address mapping, destination selection, security,
privacy, group isolation, various QoS requirements etc. Many of
these additional needs or purposes have resulted in the development
of extended and distinct systems, such as DNS, patched firewall, DPI,
and CDN, etc. These systems have worked well but with costs in terms
of quality of experience for the user, particularly with respect to
time delay, but also with respect to costs of development, deployment
and management throughout (parts of) the Internet.
An alternative approach is the integration of extra capabilities and
purposes into the routing system directly. By exchanging necessary
additional information or including such information in the packet
header, purposes beyond just reachability have found entry into the
routing system over the many years of the Internet's development.
This document presents a brief survey of solutions that, when
combined, represent a routing system beyond reachability that
effectively forms today's Internet. While this survey somewhat
relates to that presented in [I-D.king-irtf-semantic-routing-survey],
our focus here is on the identification of the underlying purpose for
developing extensions, not on the body of work that represents an
approach for doing so (named 'semantic routing' in the above draft).
However, [I-D.king-irtf-semantic-routing-survey] may be useful for
more information on the specific extensions.
Some of these extensions are intended to be deployed in limited
domains [RFC8799], while others are intended for use across the
Internet. The boundary of limited domains may also be the boundary
of purposes and semantics of information defining those purposes.
This survey is used to demonstrate the recognized need by those
having developed existing solutions for the Internet's routing system
to have multiple purposes beyond mere reachability.
Building on the survey and our summary, we recognize that, in many
parts, the Internet has already evolved into a 'multi-purpose
routing' system. However, we identify issues with the approach that
has been taken so far, namely that of purpose-specific extensions.
We assert that these issues will increasingly impede the Internet's
ability to accommodate future purposes (represented in the form of
new use cases), if we simply continue with a 'business as usual'
attitude towards developing purpose-specific solutions for them.
Instead, we position this document as the starting point for a
discussion on how to evolve the Internet routing system in a coherent
manner that will help us avoid the identified issues, while still
allowing for integrating new purposes for Internet routing as they
will emerge in the future.
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Note: This document does not discuss how routers may use policies,
that are coded in, configured at, or signaled to it, to make routing
decisions. It does neither pass comment on the advisability or
practicality of any of the proposals nor does it define any technical
solutions.
2. Reachability - Original Purpose of the Routing System
Network routing protocols were initially designed to enable
forwarding of IP packets through the network toward destination
addresses. Fundamental to this is the locator semantic of IP
addresses, which has been assigned in the context of network
topologies. The original routing system was designed on a
distributed basis. Each router makes its own decision about the
interface/link onto which it forwards a packet. Each decision takes
the packet one hop closer to the destination. However, the choices
made by distributed devices may not always work well if they are
poorly coordinated between the routers, resulting in issues, such as
forwarding loops, which may be transitory or permanent. So it is
normal to require the use of the same algorithm to decide the
forwarding actions at each hop.
A way to avoid routing issues is to select an end-to-end path a
priori and consistently execute forwarding on the intermediate
routers accordingly. This element of traffic engineering is known as
"path steering" [I-D.ietf-teas-rfc3272bis] and relies on the routing
to protocols collect and exchange the reachability within a domain,
so that any routers can select an end-to-end path . However, the
amount of information needed to support these decisions can become
very large (e.g., in large networks, with many possible paths and
route metrics), which might impede the scalability both in terms of
the storage and the distribution of the information. Although
network topology filters are often applied to reduce the storage of
the network data and the complexity of the computation algorithm, the
path computation accuracy and optimality may be negatively impacted.
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The Internet is a very complicated system that is made up of many
independently built networks with two types of routing protocols: an
interior gateway protocol (IGP) that routes inside a network and an
exterior gateway protocol (such as BGP) that routes between networks.
For a communication that crosses more than one domain, there could be
many possible paths for the given destination. In principle, the
more information that decision-making devices have, the better
choices they can make. However, it is often infeasible to have all
information of all potential end-to-end paths, particularly for
communications through several networks with different ownership.
Consequently, the best choices made within each domain may not reach
the best overall result. A key challenge here is the tussle between
abstraction, needed for scalability, and optimality, which
abstraction may impede.
When choosing the best paths or topology structures, the following
may need to be considered:
* The method by which a path, or set of paths, is to be calculated.
For example, a path may be selected automatically by the routing
protocol or may be imposed (perhaps for traffic engineering
reasons) by a central controller or management entity.
* The criteria used for selecting the best path. For example,
classic route preference, or administrative policies such as
economic costs, resilience, security, and (if requested) applying
geopolitical considerations.
3. Extension of the Routing System Beyond 'Mere' Reachability
In the following, we provide a brief overview of routing extensions
with purposes beyond 'mere' reachability. We align our overview with
many of the solutions described in
[I-D.king-irtf-semantic-routing-survey] and refer to this draft for
more detail, in addition to the example references themselves.
The following Table 1 focusses on three key aspects when considering
routing extensions for our discussion in this draft:
* Purpose: What is the intended purpose of the proposed extension?
This aspect may lead to a taxonomy for looking at the capabilities
of a multi-purpose routing system.
* Approach: What is the underlying technical approach to achieve the
intended purpose? This aspect may lead to a taxonomy of
approaches for achieving desired routing purposes.
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* Examples: What are known examples that have employed the given
approach to achieve the given routing purpose? This aspect
provides a possibly growing catalogue of explicit examples to
study in more detail.
+==============+===============+======================================+
| Purpose | Approach | Examples |
+==============+===============+======================================+
|Path Selection| Preferential | IS-IS Extensions [RFC5305] |
| for Traffic | Routing | |
| Engineering | | |
+--------------+---------------+--------------------------------------+
| | Policy-based | PBR models [RFC1104] Inter-domain |
| | Routing | policy routing [RFC1479] |
+--------------+---------------+--------------------------------------+
| | Flow Steering | TBD |
+--------------+---------------+--------------------------------------+
| | Path | PCE [RFC4655] PCEP [RFC5440] PCEP |
| | Computation | Extension [RFC8231] |
+--------------+---------------+--------------------------------------+
| | IRTF | Path-aware Networking RG [PANRGref] |
| | | Path properties |
| | |[I-D.irtf-panrg-path-properties] Past |
| | | efforts evaluation |
| | | [I-D.irtf-panrg-what-not-to-do] |
+--------------+---------------+--------------------------------------+
|Path Selection| Multicast |IP multicast [RFC1112] IPv6 addressing|
|for Multicast | | [RFC4291] MBone [MBONEref] MADCAP |
| | | [RFC2730] MALLOC [RFC6308] MASC |
| | | [RFC2909] MZAP [RFC2776] MSDP |
| | | [RFC3618] SSM [RFC4607] |
+--------------+---------------+--------------------------------------+
| | Automatic | AMT [RFC7450] |
| | Multicast | |
| | Tunneling | |
+--------------+---------------+--------------------------------------+
| | Path-based | BIER [RFC8279] BIER encapsulation |
| | Forwarding | [RFC8296] IP-over-ICN |
| | |[I-D.trossen-icnrg-internet-icn-5glan]|
+--------------+---------------+--------------------------------------+
| Routing | Future | [RESEARCHFIAref] [ITUNET2030ref] |
|Architectures | architectures | [SCIONref] [RINAref] |
+--------------+---------------+--------------------------------------+
| Service | L2/L3 Explicit| SFC [RFC7665] NSH [RFC8300] MPLS |
| Function |Header Chaining| encapsulation [RFC8596] |
| Chaining | | |
+--------------+---------------+--------------------------------------+
| | Name-based | Name-based SFF [RFC8677] |
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| | Chaining | |
+--------------+---------------+--------------------------------------+
| | Source Routing| Segment Routing [RFC8402] |
+--------------+---------------+--------------------------------------+
| Application/ | Application- | Aalto [RFC7285] APN |
|service-aware | server based | [I-D.li-apn-framework] |
| Routing | | |
+--------------+---------------+--------------------------------------+
| | L3 based | Dyncast use cases |
| | |[I-D.liu-dyncast-ps-usecases] Dyncast |
| | | use architecture |
| | | [I-D.li-dyncast-architecture] |
+--------------+---------------+--------------------------------------+
| | Network | Segment routing [RFC8986] |
| | programming | |
+--------------+---------------+--------------------------------------+
| Anycast | IP Anycast | Architcture considerations[RFC7094] |
| Routing | | Operation of Anycast [RFC4786] |
+--------------+---------------+--------------------------------------+
| | Metric-based | Dyncast use cases |
| | |[I-D.liu-dyncast-ps-usecases] Dyncast |
| | | architecture |
| | | [I-D.li-dyncast-architecture] Load- |
| | | balanced anycast [weightedRef] |
+--------------+---------------+--------------------------------------+
|Privacy-aware | Crypto routing| CGA [RFC3972] CGA Extension Field |
| Routing | | [RFC4581] |
+--------------+---------------+--------------------------------------+
| | Obfuscation | ILNP-based [ILNP_PRIVACY] |
+--------------+---------------+--------------------------------------+
| Security- | Routing | SCION [SCIONref] |
| enhanced | Architecture | |
| Routing | | |
+--------------+---------------+--------------------------------------+
|Identity Split| Identity/ | LISP [RFC6830] LISPbis |
| Routing | Locator Split | [I-D.ietf-lisp-rfc6830bis] LISPbis |
| | | [I-D.ietf-lisp-rfc6833bis] |
| | | HIP[RFC4423] ILNP [RFC6740] |
+--------------+---------------+--------------------------------------+
| Content | Routing over | ICN [ICNref] NDN [NDNref] ICN |
| Routing | content names | deployment [RFC8763] HICN [HICNref] |
+--------------+---------------+--------------------------------------+
| | Routing via | DNS DONA [DONAref] |
| | indirection | |
| | points | |
+--------------+---------------+--------------------------------------+
|Differentiated| QoS | DiffServ [RFC2474] IntServ [RFC2210] |
| Routing |Differentiation| |
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+--------------+---------------+--------------------------------------+
| | Path | Segment Routing [RFC8402] SFC |
| |differentiation| [RFC7665] |
+--------------+---------------+--------------------------------------+
| Extended | EH-based | IPv6 EH [RFC8200] |
| Routing | | |
+--------------+---------------+--------------------------------------+
Table 1: Summary of Routing Extensions
4. Issues with Current Approaches
Developing routing purposes beyond the original 'mere' reachability
does come with issues when considering their deployment and use in
the Internet; we outline those issues in the following.
We note that those issues are intrisincely linked to the ones
stemming from the extension of addressing semantics that may be used
to realize the various routing extensions, identified in
[I-D.jia-intarea-internet-addressing-gap-analysis]. We therefore
structure our presentation along the same lines.
4.1. Limiting Routing Semantics
Approaches that intend to change the purpose of communication, e.g.,
by separating host from network node identification [RFC7401] or
through identification of content directly [HICNref], are limited by
the reachability purpose of IPv6, as defined by its source and
destination address.
This leads to approaches such as
[I-D.trossen-icnrg-internet-icn-5glan] to override addressing
semantics, namely replacing the IPv6 source and destination addresses
with path information instead, in order to achieve the desired
purpose of its routing solution. This, in turn, requires to still
carry address information as part of the payload in order to support
clients unaware of the routing extension. Furthermore, such approach
may lead to 'information leakage'outside the boundaries of the system
in which its changed purpose is being realized. Introduction of
dedicated gateways to 'translate' from one purpose (new routing) to
another (IPv6 routing) is the consequence of this.
But even such approach of 're-writing' packet information towards a
new purpose limits the expressible (new) semantic information to the
size of the original field, thereby limiting the support of content
information in approaches such as [HICNref] or the size of supported
networks in [I-D.trossen-icnrg-internet-icn-5glan] to the bit size
afforded by IPv6 addresses.
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4.2. Complexity and Efficiency
Introducing new routing purposes also bring additional complexity.
This becomes an issue when new purposes are being introduced in
particular parts of the overall Internet, such as the edge of the
network, while relying on the existing reachability purpose of the
Internet to interconnect those islands over the existing Internet.
This additional complexity therefore often comes with a penalty in
the form of efficiency and costs for realizing the novel routing
purpose, which in turn may specifically pose an even bigger problem
when the solution is introduced at the edge of the network, which is
often constrained in resources and therefore costs that can be
expensed.
For instance, if the specific new purpose requires compression of
packet fields, such as for header compression, additional processing
as well as potentially required gateways that restore information
towards the Internet may be prohibitive for introducing the desired
new routing purpose in this part of the Internet.
Conversely, performance requirements of core networks, in terms of
packet processing speed, pose a problem when wanting to accommodate
novel routing purposes. Here, not only the possibly additional
processing but also the required changes of often HW-based platforms
makes adoption of novel routing purposes prohibitive.
4.2.1. Repetitive encapsulation
A routing solution targetting a different purposes often requires
encapsulating the relevant information, thereby bloating packet sizes
and lowering overall efficiency. This can be seen in routing
solutions such as [I-D.trossen-icnrg-internet-icn-5glan] (introducing
an alternative forwarding solution), [I-D.ietf-lisp-mn] (handling
mobility in LISP), [RFC8926] and [RFC7348] (DC networking), [RFC8986]
(traffic engineering) as well as [TOR] (routing privacy), all of
which introduce multiple encapsulations that in turn reduce the
forwarding effiency.
The introduction of dedicated points of encapsulation also introduce
complexity and costs at the points of the network where they are
required, which may often be at the network edge, while also
establishing failure points and therefore increasing the overall
fragility of the system; a point we discuss in more detail in
Section 4.4.
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4.2.2. Introducing Path Stretch
Path stretch is an issue when moving from direct reachability
purposes to additional ones, such as dealing with mobility of
endpoints, as done in MobileIP [RFC6275]. In this case, following
the typical triangular route affects transmission effiency as well as
overall latency of the communication, instead of communicating
directly towards the (new) network location.
Additionally, the realization of novel purposes, such as privacy-
compliant routing in systems like TOR [TOR], often introduce path
stretch due to the additional relays being introduced for fulfilling
the intended purpose, here the obfuscation of traffic for privacy
reasons.
4.2.3. Complicating Traffic Engineering
As outlined in Section 3, many solutions to extend the original
reachability purpose of Internet routing aim to introduce or improve
on traffic engineering capabilities, e.g., by enabling decisions
based on QoS metrics, mobility, chaining and others aspects.
However, realizing each novel purpose as a separate solution in
itself likely hampers the goal for which they are developed, namely
to improve on traffic engineering, whenever individual solutions are
being used in combination. This 'feature interaction' aspect may
even prevent combined uses, while at a minimum requiring an
understanding if combined uses are possible in the first place or
instead incompatible with each other. This is not just an issue that
routing purposes may be incompatible at a functional level, e.g.,
through conflicting policies, but may also utilize conflicting
realizations for their purposes.
4.3. Security
Security issues, outside the security considerations of the specific
design, often arise from the integration of the specific solution
into the existing routing system. For instance, HIP [RFC7401] limits
its host identity to 128bit in an effort to be backward compatible,
but possibly resulting in weak cryptographical strength. A similar
issue can be observed in CGA [RFC3972], where only 59bits of the
128bit limit may be used for what could be packet signatures not
sufficiently robust enough against attacks.
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Attempts to introduce privacy purposes into the routing system, e.g.,
by utilizing ephemeral addresses
[I-D.gont-v6ops-ipv6-addressing-considerations], may in turn pose
significant challenges on the routing system through its required
renewal rate of addresses.
4.4. Fragility
From the overview of novel routing purposes in Section 3, we can
observe that the existence of those additional routing purpose adds
many purpose-specific translation/adaptation points, responsible for
mapping formats from one meaningful context into another. This is in
turn creates dependency on this additional functionality to exist for
endpoints to communicate with the context of the intended purpose.
While translation/adaptation between purposes and their defining
contexts is often not avoidable when going beyond 'mere'
reachabiulity, it is the solution-specific nature of those components
(required for many if not each extended purpose) that is likely to
increase the fragility of the resulting system.
The key problem here is the interaction with other extended purposes
that may exist in specific deployments. While needing to operate in
the presence of those other purpose-specific components, their design
has often not taken into account the specific interaction in
question. Given the diversity of extension realizations, utilizing
many, almost any packet field, even beyond and entirely different to
its intentded purpose, conflicting behaviour as well as diverging
interpretatin of the utilized packet information is clearly an issue.
Only careful testing of combinations with possible delineation (of
purposes) as well as networks may be required, all of which further
increases the costs for utilizing the extended purposes.
4.5. Interoperability
Although routing extensions are developed with their specific
purposes in mind, reflected in requirements and behaviours, they are
often realized in conjunction with other extensions when it comes to
real-world deployments.
This poses an Interoperability challenge, both in terms of backward
as well as forward compability. Feature interactions need
investigations, often left to operational deployment.
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Building extensions on the basis of agreed packet field semantics is
one way to achieve the desired interoperability, unless approaches
use extensions to packet fields beyond their original intention. As
a consequence, translation/adaptation points may be needed to ensure
interoperability with other parts of the network, increasing the
fragility of the system, as discussed in Section 4.4.
Forward compability aims at ensuring that future extensions will
continue to be possible, aiming at an overall extensibility of the
system beyond its purpose at the time of developing a specific
solution. IPv6 extension headers are one example of enabling future
extensions, although not without their own problems in real-world
deployments [SHIMv6ref].
5. Where to Go From Here?
This document outlined the original starting point of the Internet's
routing system, namely providing 'mere' reachability, and showed
through its survey of existing solutions that have since been
developed that Internet routing has, in fact, evolved into a system
that serves many purposes beyond its original 'mere' reachability
goal.
However, the issues we outlined in Section 4 pose the question on how
to move forward in the (future) evolution of Internet routing. We
assert that continuing with a 'business as usual' attitude will
ultimately compound the identified issues, thereby hampering
innovation in novel routing purposes and solutions, and therefore the
Internet overall.
As a way forward, we ask the wider RTG WG community to recognize the
following cornerstones for an evolution path for Internet routing:
1. Further evolution of the Internet's routing system MUST take a
wider architectural approach in order to break with the point
solution approach that has led to the identified issues in
Section 4.
2. With research and development on routing solutions continuing, as
also illustrated in [I-D.king-irtf-semantic-routing-survey],
these works MUST be brought into the process of IETF engagement
and standardization to increase the understanding of what novel
trends, works, and possible developments may be just around the
corner but also to inform ongoing research and development on
paths taken in the IETF.
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3. The RTG WG SHOULD play a role in the engagement with research and
development since the 'Future of Internet Routing' (FIR) is at
the heart of its charter ("The Routing Area working group (RTGWG)
is chartered to provide a venue to discuss, evaluate, support and
develop proposals for new work in the Routing Area" [RTGWGref]),
a role that goes beyond the "specific small topics that do not
fit with an existing working group" [RTGWGref].
Following on the cornerstones outlined above, we specifically suggest
to the RTG WG, aligned with its charter to consider the following
actions:
1. Establish suitable efforts within the RTG WG (e.g., as a sub-
group) OR
2. Support the establishment of suitable efforts as a standalone FIR
WG OR
3. Support the establishment of suitable efforts within the IRTF,
where those efforts directly liaise with the RTG WG through
regular updates in its meetings.
6. Security Considerations
Section 4.3 outlines a number of security issues that may occur
outside the solution-specific security considerations, such as
interactions between protocol behaviours that were previously
untested as a combination. With that in mind, security
considerations for a wider architectural approach to routing must
have the security of the overall routing system as the main goal, not
merely the security of a single solution.
7. Privacy Considerations
Protecting user privacy is very important. This extends beyond
ensuring that user data cannot be examined in transit, and also
requires that a process that inspects the network traffic should not
be able to determine which applications or what types of application
a user is running.
This makes it critically important to minimize or entirely avoid user
and/or application information to be directly used for routing
purposes. Instead, applications (or users) should express
requirements for traffic delivery in a manner that does not reveal
information about the user.
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Encryption of user data, which is a common technique to protect user
privacy, may obscure information that has previously been used to
perform enhanced routing (such as by inspecting or hashing on payload
fields), demonstrating that new requirements (here on privacy) may
negatively impact previously accepted solutions.
8. IANA Considerations
This draft does not request any IANA action.
9. Acknowledgements
TBD.
10. Contributors
Adrian Farrel
Email: adrian@olddog.co.uk
11. Informative References
[CLNPref] "Protocol for providing the connectionless-mode network
service: Protocol specification - Part 1",
standard ISO/IEC 8473-1:1998, 1998,
<https://www.iso.org/standard/30931.html>.
[CONTENTref]
Choi, J., Han, J., and E. Cho, "A survey on content-
oriented networking for efficient content delivery",
Paper IEEE Communications Magazine, 49(3): 121-127, May
2011., 2011, <https://ieeexplore.ieee.org/
iel5/35/5723785/05723809.pdf>.
[DONAref] Koponen, T., Chawla, M., Chun, B.-G., Ermolinskiy, A.,
Kim, K. H., Shenker, S., and I. Stoica, "A data-oriented
(and beyond) network architecture", Paper Proceedings of
the 2007 conference on Applications, technologies,
architectures, and protocols for computer communications,
August 2007, 2007,
<https://dl.acm.org/doi/10.1145/1282380.1282402>.
[HICNref] Carofiglio, G., Muscariello, L., Auge, J., Papalini, M.,
Sardara, M., and A. Compagno, "Enabling ICN in the
Internet Protocol: Analysis and Evaluation of the Hybrid-
ICN Architecture", Paper Proceedings of the 6th ACM
Conference on Information-Centric Networking, 2019., 2019,
Trossen, et al. Expires 12 August 2022 [Page 14]
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<https://www.researchgate.net/publication/336344520_Enabli
ng_ICN_in_the_Internet_Protocol_Analysis_and_Evaluation_of
_the_Hybrid-ICN_Architecture>.
[I-D.bonica-6man-ext-hdr-update]
Bonica, R. and T. Jinmei, "Inserting, Processing And
Deleting IPv6 Extension Headers", Work in Progress,
Internet-Draft, draft-bonica-6man-ext-hdr-update-06, 30
August 2021, <https://www.ietf.org/archive/id/draft-
bonica-6man-ext-hdr-update-06.txt>.
[I-D.bryant-arch-fwd-layer-ps]
Bryant, S., Chunduri, U., Eckert, T., and A. Clemm,
"Forwarding Layer Problem Statement", Work in Progress,
Internet-Draft, draft-bryant-arch-fwd-layer-ps-04, 24
January 2022, <https://www.ietf.org/archive/id/draft-
bryant-arch-fwd-layer-ps-04.txt>.
[I-D.chunduri-lsr-isis-preferred-path-routing]
Chunduri, U., Li, R., White, R., Contreras, L. M.,
Tantsura, J., and Y. Qu, "Preferred Path Routing (PPR) in
IS-IS", Work in Progress, Internet-Draft, draft-chunduri-
lsr-isis-preferred-path-routing-07, 12 November 2021,
<https://www.ietf.org/archive/id/draft-chunduri-lsr-isis-
preferred-path-routing-07.txt>.
[I-D.farrel-irtf-introduction-to-semantic-routing]
Farrel, A. and D. King, "An Introduction to Semantic
Routing", Work in Progress, Internet-Draft, draft-farrel-
irtf-introduction-to-semantic-routing-03, 22 January 2022,
<https://www.ietf.org/archive/id/draft-farrel-irtf-
introduction-to-semantic-routing-03.txt>.
[I-D.gont-v6ops-ipv6-addressing-considerations]
Gont, F. and G. Gont, "IPv6 Addressing Considerations",
Work in Progress, Internet-Draft, draft-gont-v6ops-ipv6-
addressing-considerations-01, 21 February 2021,
<https://www.ietf.org/archive/id/draft-gont-v6ops-ipv6-
addressing-considerations-01.txt>.
[I-D.ietf-lisp-mn]
Farinacci, D., Lewis, D., Meyer, D., and C. White, "LISP
Mobile Node", Work in Progress, Internet-Draft, draft-
ietf-lisp-mn-11, 30 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-lisp-mn-
11.txt>.
Trossen, et al. Expires 12 August 2022 [Page 15]
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[I-D.ietf-lisp-rfc6830bis]
Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, "The Locator/ID Separation Protocol (LISP)",
Work in Progress, Internet-Draft, draft-ietf-lisp-
rfc6830bis-36, 18 November 2020,
<https://www.ietf.org/archive/id/draft-ietf-lisp-
rfc6830bis-36.txt>.
[I-D.ietf-lisp-rfc6833bis]
Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
"Locator/ID Separation Protocol (LISP) Control-Plane",
Work in Progress, Internet-Draft, draft-ietf-lisp-
rfc6833bis-30, 18 November 2020,
<https://www.ietf.org/archive/id/draft-ietf-lisp-
rfc6833bis-30.txt>.
[I-D.ietf-teas-rfc3272bis]
Farrel, A., "Overview and Principles of Internet Traffic
Engineering", Work in Progress, Internet-Draft, draft-
ietf-teas-rfc3272bis-13, 8 November 2021,
<https://www.ietf.org/archive/id/draft-ietf-teas-
rfc3272bis-13.txt>.
[I-D.ietf-v6ops-ipv6-ehs-packet-drops]
Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
G., and W. (. Liu, "Operational Implications of IPv6
Packets with Extension Headers", Work in Progress,
Internet-Draft, draft-ietf-v6ops-ipv6-ehs-packet-drops-08,
11 June 2021, <https://www.ietf.org/archive/id/draft-ietf-
v6ops-ipv6-ehs-packet-drops-08.txt>.
[I-D.irtf-panrg-path-properties]
Enghardt, T. and C. Kraehenbuehl, "A Vocabulary of Path
Properties", Work in Progress, Internet-Draft, draft-irtf-
panrg-path-properties-04, 25 October 2021,
<https://www.ietf.org/archive/id/draft-irtf-panrg-path-
properties-04.txt>.
[I-D.irtf-panrg-what-not-to-do]
Dawkins, S., "Path Aware Networking: Obstacles to
Deployment (A Bestiary of Roads Not Taken)", Work in
Progress, Internet-Draft, draft-irtf-panrg-what-not-to-do-
19, 26 March 2021, <https://www.ietf.org/archive/id/draft-
irtf-panrg-what-not-to-do-19.txt>.
[I-D.jia-intarea-internet-addressing-gap-analysis]
Jia, Y., Trossen, D., Iannone, L., Shenoy, N., and P.
Mendes, "Gap Analysis in Internet Addressing", Work in
Trossen, et al. Expires 12 August 2022 [Page 16]
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Progress, Internet-Draft, draft-jia-intarea-internet-
addressing-gap-analysis-01, 23 October 2021,
<https://www.ietf.org/archive/id/draft-jia-intarea-
internet-addressing-gap-analysis-01.txt>.
[I-D.king-irtf-semantic-routing-survey]
King, D. and A. Farrel, "A Survey of Semantic Internet
Routing Techniques", Work in Progress, Internet-Draft,
draft-king-irtf-semantic-routing-survey-03, 26 November
2021, <https://www.ietf.org/archive/id/draft-king-irtf-
semantic-routing-survey-03.txt>.
[I-D.li-apn-framework]
Li, Z., Peng, S., Voyer, D., Li, C., Liu, P., Cao, C.,
Mishra, G., Ebisawa, K., Previdi, S., and J. N. Guichard,
"Application-aware Networking (APN) Framework", Work in
Progress, Internet-Draft, draft-li-apn-framework-04, 25
October 2021, <https://www.ietf.org/archive/id/draft-li-
apn-framework-04.txt>.
[I-D.li-dyncast-architecture]
Li, Y., Iannone, L., Trossen, D., Liu, P., and C. Li,
"Dynamic-Anycast Architecture", Work in Progress,
Internet-Draft, draft-li-dyncast-architecture-01, 20
January 2022, <https://www.ietf.org/archive/id/draft-li-
dyncast-architecture-01.txt>.
[I-D.liu-dyncast-ps-usecases]
Liu, P., Willis, P., Trossen, D., and C. Li, "Dynamic-
Anycast (Dyncast) Use Cases & Problem Statement", Work in
Progress, Internet-Draft, draft-liu-dyncast-ps-usecases-
02, 17 January 2022, <https://www.ietf.org/archive/id/
draft-liu-dyncast-ps-usecases-02.txt>.
[I-D.muscariello-intarea-hicn]
Muscariello, L., Carofiglio, G., Augé, J., Papalini, M.,
and M. Sardara, "Hybrid Information-Centric Networking",
Work in Progress, Internet-Draft, draft-muscariello-
intarea-hicn-04, 20 May 2020,
<https://www.ietf.org/archive/id/draft-muscariello-
intarea-hicn-04.txt>.
Trossen, et al. Expires 12 August 2022 [Page 17]
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[I-D.trossen-icnrg-internet-icn-5glan]
Trossen, D., Robitzsch, S., Reed, M., Al-Naday, M., and J.
Riihijarvi, "Internet Services over ICN in 5G LAN
Environments", Work in Progress, Internet-Draft, draft-
trossen-icnrg-internet-icn-5glan-04, 1 October 2020,
<https://www.ietf.org/archive/id/draft-trossen-icnrg-
internet-icn-5glan-04.txt>.
[ICNref] Barbera, D., Xylomenos, G., Ververidis, C., Siris, V., and
N. Fotiou, "A Survey of information-centric networking
research", Paper IEEE Communications Surveys and
Tutorials, vol. 16, Iss. 2, Q2 2014, 2014,
<https://www.scopus.com/record/
display.uri?eid=2-s2.0-84901242669>.
[ILNP_PRIVACY]
Bhatti, S., Haywood, G., and R. Yanagida, "End-to-end
privacy for identity and location with IP", Paper 2nd
Workshop on New Internetworking Protocols, Architecture
and Algorithms, 29th IEEE International Conference on
Network Protocols, 2021.
[ISISref] "Intermediate System to Intermediate System intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode network service", standard ISO/IEC
10589, 2002, <https://standards.iso.org/ittf/
PubliclyAvailableStandards/
c030932_ISO_IEC_10589_2002(E).zip>.
[ITUNET2030ref]
"Network 2030 Architecture Framework", Technical
Specification ITU-T Focus Group on Technologies for
Network 2030, 2020, <https://www.itu.int/en/ITU-
T/focusgroups/net2030/Documents/Network_2030_Architecture-
framework.pdf>.
[MBONEref] Savetz, K., Randall, N., and Y. Lepage, "MBONE:
Multicasting Tomorrow's Internet", Book IDG, 1996,
<https://www.savetz.com/mbone/>.
[NDNref] Zhang, L., Afanasyev, A., and J. Burke, "Named Data
Networking", Paper ACM SIGCOMM Computer Communication,
Review 44(3): 66-73, 2014, 2014.
[PANRGref] "Path Aware Networking Research Group", RG Path Aware
Networking Research Group,
<https://datatracker.ietf.org/rg/panrg/about>.
Trossen, et al. Expires 12 August 2022 [Page 18]
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[RESEARCHFIAref]
Pan, J., Paul, S., and R. Jain, "A Survey of the Research
on Future Internet Architectures", Paper IEEE
Communications Magazine, vol. 49, no. 7, July 2011, 2014,
<https://ieeexplore.ieee.org/document/5936152>.
[RFC1069] Callon, R. and H. Braun, "Guidelines for the use of
Internet-IP addresses in the ISO Connectionless-Mode
Network Protocol", RFC 1069, DOI 10.17487/RFC1069,
February 1989, <https://www.rfc-editor.org/info/rfc1069>.
[RFC1104] Braun, H., "Models of policy based routing", RFC 1104,
DOI 10.17487/RFC1104, June 1989,
<https://www.rfc-editor.org/info/rfc1104>.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC1479] Steenstrup, M., "Inter-Domain Policy Routing Protocol
Specification: Version 1", RFC 1479, DOI 10.17487/RFC1479,
July 1993, <https://www.rfc-editor.org/info/rfc1479>.
[RFC2210] Wroclawski, J., "The Use of RSVP with IETF Integrated
Services", RFC 2210, DOI 10.17487/RFC2210, September 1997,
<https://www.rfc-editor.org/info/rfc2210>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address
Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
DOI 10.17487/RFC2730, December 1999,
<https://www.rfc-editor.org/info/rfc2730>.
[RFC2776] Handley, M., Thaler, D., and R. Kermode, "Multicast-Scope
Zone Announcement Protocol (MZAP)", RFC 2776,
DOI 10.17487/RFC2776, February 2000,
<https://www.rfc-editor.org/info/rfc2776>.
Trossen, et al. Expires 12 August 2022 [Page 19]
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[RFC2909] Radoslavov, P., Estrin, D., Govindan, R., Handley, M.,
Kumar, S., and D. Thaler, "The Multicast Address-Set Claim
(MASC) Protocol", RFC 2909, DOI 10.17487/RFC2909,
September 2000, <https://www.rfc-editor.org/info/rfc2909>.
[RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path
Algorithm", RFC 2992, DOI 10.17487/RFC2992, November 2000,
<https://www.rfc-editor.org/info/rfc2992>.
[RFC3618] Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
Discovery Protocol (MSDP)", RFC 3618,
DOI 10.17487/RFC3618, October 2003,
<https://www.rfc-editor.org/info/rfc3618>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, DOI 10.17487/RFC4423, May
2006, <https://www.rfc-editor.org/info/rfc4423>.
[RFC4581] Bagnulo, M. and J. Arkko, "Cryptographically Generated
Addresses (CGA) Extension Field Format", RFC 4581,
DOI 10.17487/RFC4581, October 2006,
<https://www.rfc-editor.org/info/rfc4581>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>.
[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/info/rfc4655>.
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
December 2006, <https://www.rfc-editor.org/info/rfc4786>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
Trossen, et al. Expires 12 August 2022 [Page 20]
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[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
2011, <https://www.rfc-editor.org/info/rfc6275>.
[RFC6308] Savola, P., "Overview of the Internet Multicast Addressing
Architecture", RFC 6308, DOI 10.17487/RFC6308, June 2011,
<https://www.rfc-editor.org/info/rfc6308>.
[RFC6740] Atkinson, RJ. and SN. Bhatti, "Identifier-Locator Network
Protocol (ILNP) Architectural Description", RFC 6740,
DOI 10.17487/RFC6740, November 2012,
<https://www.rfc-editor.org/info/rfc6740>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.
[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/info/rfc7285>.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
<https://www.rfc-editor.org/info/rfc7348>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
Trossen, et al. Expires 12 August 2022 [Page 21]
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[RFC7450] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450,
DOI 10.17487/RFC7450, February 2015,
<https://www.rfc-editor.org/info/rfc7450>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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[RFC8596] Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
"MPLS Transport Encapsulation for the Service Function
Chaining (SFC) Network Service Header (NSH)", RFC 8596,
DOI 10.17487/RFC8596, June 2019,
<https://www.rfc-editor.org/info/rfc8596>.
[RFC8677] Trossen, D., Purkayastha, D., and A. Rahman, "Name-Based
Service Function Forwarder (nSFF) Component within a
Service Function Chaining (SFC) Framework", RFC 8677,
DOI 10.17487/RFC8677, November 2019,
<https://www.rfc-editor.org/info/rfc8677>.
[RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <https://www.rfc-editor.org/info/rfc8684>.
[RFC8736] Venaas, S. and A. Retana, "PIM Message Type Space
Extension and Reserved Bits", RFC 8736,
DOI 10.17487/RFC8736, February 2020,
<https://www.rfc-editor.org/info/rfc8736>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8763] Rahman, A., Trossen, D., Kutscher, D., and R. Ravindran,
"Deployment Considerations for Information-Centric
Networking (ICN)", RFC 8763, DOI 10.17487/RFC8763, April
2020, <https://www.rfc-editor.org/info/rfc8763>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
[RFC8926] Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
"Geneve: Generic Network Virtualization Encapsulation",
RFC 8926, DOI 10.17487/RFC8926, November 2020,
<https://www.rfc-editor.org/info/rfc8926>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
Trossen, et al. Expires 12 August 2022 [Page 23]
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[RINAref] Day, J., "Patterns in Network Architecture: A Return to
Fundamentals", Book Prentice Hall, 2008.
[RTGWGref] "Routing Working Group Charter", WG Routing Working Group,
<https://datatracker.ietf.org/wg/rtgwg/charter/>.
[SCIONref] Barbera, D., Chaut, L., Perrig, A., Reischuk, R., and P.
Szalachowski, "Patterns in Network Architecture: A Return
to Fundamentals", Paper The ACM, vol. 60, no. 6, June
2017, 2017,
<https://icnp20.cs.ucr.edu/Slides/NIPAA/D-3_invited.pptx>.
[SHIMv6ref]
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Authors' Addresses
Dirk Trossen
Huawei Technologies
Munich
Germany
Email: dirk.trossen@huawei.com
David Lou
Huawei Technologies
Munich
Germany
Email: zhe.lou@huawei.com
Trossen, et al. Expires 12 August 2022 [Page 24]
Internet-Draft Multi-Purpose Routing System February 2022
Sheng Jiang
Huawei Technologies
China
Email: jiangsheng@huawei.com
Trossen, et al. Expires 12 August 2022 [Page 25]