Internet DRAFT - draft-abraitis-extcommunity-paths
draft-abraitis-extcommunity-paths
Interdomain Routing R. White
Internet-Draft Akamai, Inc.
Intended status: Standards Track D. Abraitis
Expires: 13 July 2023 NetDef
9 January 2023
BGP Available Paths Count Extended Community
draft-abraitis-extcommunity-paths-00
Abstract
This document defines a new BGP Opaque Extended Community to carry
the number of paths available for an arbitrary prefix.
Status of This Memo
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This Internet-Draft will expire on 13 July 2023.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . 2
3. Available Paths Count Extended Community . . . . . . . . . . 2
4. Deployment Considerations . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
This document defines a new BGP Opaque Extended Community to carry
the number of paths available for an arbitrary prefix. BGP speakers
that receive this extended community can configure local instance to
influence their decision process by preferring routes with a higher
number of paths over others.
[RFC7911] defines a BGP extension to send multiple paths for the same
address prefix without the new paths implicitly replacing any
previous ones. However, if the ADD-PATH capability is not possible
to use between BGP speakers, Available Paths Count Extended Community
can be another way to prefer a prefix which has more paths.
2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Available Paths Count Extended Community
This is an Transitive Opaque Extended Community [RFC4360] with the
following encoding:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x03 | TBD | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
1. The value of the high-order octet of the extended Type field is
0x03, which indicates it is transitive.
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2. The value of the low-order octet of the extended Type field as
assigned by IANA is TBD.
3. Reserved field MUST be set to 0 and ignored upon the receipt of
this community.
4. The last octet of the extended community is an unsigned integer
that gives the count of the available paths for an arbitrary
prefix.
4. Deployment Considerations
If the BGP speaker supports the extension defined in this document,
it SHOULD attach the Available Paths Count Extended Community to BGP
UPDATE messages sent to iBGP peers implicitly.
The receiving BGP speaker, SHOULD derive a count of available paths
from the last octet of the extended community if present.
An implementation SHOULD NOT send more than one instance of the
Available Paths Count extended community.
By default, an implementation SHOULD NOT send this extended community
to eBGP peers. However, it SHOULD be possible to configure an
implementation to send or accept the community when configured.
The implementation SHOULD provide a way to explicitly disable sending
this community.
Also, the implementation could provide an OPTIONAL way to involve
Available Paths Count Extended Community into the best path selection
process. The prefix with the higher count of paths SHOULD win. If
at least one of the routes does not have Available Paths Count
Extended Community, the best path selection process is not affected,
and this step is ignored. If both routes have the community, defined
in this extension, the normal BGP decision is changed so that the
Available Paths Count Extended Community is checked before Multi Exit
Discriminator (MED). It MUST be possible to enable or disable this
extra step (comparing Available Paths Count Extended Community) in
the best path selection process.
If the count of paths changed, the implementation SHOULD NOT send an
UPDATE immediately. Available Paths Count Extended Community SHOULD
be adjusted only when the best path changes.
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5. IANA Considerations
This memo requests IANA assign a number from the Transitive Opaque
Extended Community Sub-Types registry for "Available Paths Count"
extended community. Registration procedures come under the First
Come First Served.
6. Normative References
[RFC2119] Bradner, S. and RFC Publisher, "Key words for use in RFCs
to Indicate Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
Authors' Addresses
Russ White
Akamai, Inc.
Email: russ@riw.us
Donatas Abraitis
NetDef
Email: donatas.abraitis@gmail.com
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