Network Working Group K. Patel
Internet-Draft A. Lindem
Intended status: Standards Track Cisco Systems
Expires: January 9, 2017 L. Jalil
Verizon
July 8, 2016
Selective Advertisement of Multiple Paths within BGP
draft-keyupate-idr-bgp-selective-add-paths-01.txt
Abstract
[draft-ietf-idr-add-paths] defines a BGP extension that allows the
advertisement of multiple paths for the same address prefix without
the new paths implicitly replacing any previous ones. The essence of
the extension is that each path is identified by a path identifier in
addition to the address prefix. This draft augments functionality
defined in [draft-ietf-idr-add-paths] to facilitate advertisement of
multiple paths for a subset of prefixes in a given address family.
Prefixes are selected through specification of a well-known BGP
extended community.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Selective Add-Path Capability . . . . . . . . . . . . . . . . 3
3. Selective Add-Path Community . . . . . . . . . . . . . . . . 4
4. Selective Add-Path Use Case . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6.1. Acknowledgements . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Information References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[I-D.ietf-idr-add-paths] defines a BGP extension that allows the
advertisement of multiple paths for the same address prefix without
the new paths implicitly replacing any previous ones. The essence of
the extension is that each path is identified by a path identifier in
addition to the address prefix. This document augments functionality
defined in defined in [I-D.ietf-idr-add-paths] to facilitate
advertisement of multiple paths for a subset of prefixes in a given
address family. Prefixes are selected through specification of a
reserved BGP extended community.
This draft defines a capability to limit the scope of BGP multiple
path advertisement to a subset prefixes in a given address family.
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Prefixes are selected through specification of a reserved BGP
extended community [RFC4360].
------
P1--> | R1 |
P2--> ------ \ ------ ------
-- | RR | -- | R3 |
------ / ------ ------
P1--> | R2 |
P2--> ------
As an example, suppose that RR is a route reflector that doesn't
change nexthops of the prefixes it reflects, with clients R1, R2 and
R3. Suppose R1 sends RR an UPDATE: <NLRI=P1, NH=R1> and <NLRI=P2,
NH=R1>. Suppose R2 sends RR an UPDATE: <NLRI=P1,NH=R2> and
<NLRI=P2,NH=R2>. R1, R2, and R3 would like selective ADDPATHs for
Prefix P1 and not for Prefix P2. R1, R2, and R3 exchange selective
the ADDPATH capability with RR. R1, R2, R3 are configured with the
reserved selective ADDPATHs community that they attach to prefixes
that need selective ADDPATHs. RR now has two paths to P1 and P2. RR
announces P2 with bestpath to all its clients while RR announces P1
with additional paths. The number of additional paths with its best
path and its additional paths is a matter of local policy configured
on RR.
1.1. Requirements Language
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 RFC 2119 [RFC2119].
2. Selective Add-Path Capability
The ADD-PATH Capability is a new BGP capability [RFC5492]. The
Capability Code for this capability is allocated by IANA as specified
in the Section 5. The Capability Length field of this capability is
variable. The Capability Value field consists of one or more of the
following tuples:
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+------------------------------------------------+
| Address Family Identifier (2 octets) |
+------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+------------------------------------------------+
The meaning and use of the fields are as follows:
Address Family Identifier (AFI):
This field is the same as the one used in [RFC4760].
Subsequent Address Family Identifier (SAFI):
This field is the same as the one used in [RFC4760].
A BGP Speaker that wishes to announce or receive multiple paths MUST
exchange the add-path capability defined in [I-D.ietf-idr-add-paths].
A BGP Speaker that wishes to announce or receive multiple paths for
selected prefixes MUST exchange the selective add-path capability
defined in this draft. A BGP speaker wanting to advertise selective
add-path capability MUST also advertise the add-path capability
defined in [I-D.ietf-idr-add-paths].
In processing a received selective add-path capability from a peer, a
BGP speaker MUST ensure that it also received the add-path capability
defined in [I-D.ietf-idr-add-paths]. Otherwise, the BGP speaker
should ignore the received selective add-path capability and follow
the error handling rules for unsupported add-path capabilites in
[RFC5492].
3. Selective Add-Path Community
Upon successful Selective Add-Path capability negotiation, a BGP
speaker MUST NOT announce multiple paths for any AFI/SAFI prefix
unless it has received at least one UPDATE for that prefix that
includes the Selective Add-Path well-known community in its
attributes. The community is a Transitive Opaque Extended Community
with the sub-type value IANA-TBD.
If Selective Add-Path capability negotiation for a given AFI/SAFI has
not taken place and the Selective Add-Path Community is included with
a prefix advertised for the same AFI/SAFI, the Selective Add-Path
Community will be ignored. However, the occurance of the unexpected
community SHOULD be logged.
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4. Selective Add-Path Use Case
A use case is a BGP deployment where underlay and overlay routes are
associated with the same AFI/SAFI and, due to scaling, only multiple
paths are only advertised and installed for underlay routes. For
direct BGP sessions, the ingress routers would only advertise
multiple paths for the underlay routes. However, if the topology
includes BGP Router Reflectors [RFC4456], it is likely that multiple
ingress routers will advertise the same overlay routes. In this
case, the mechanism describe herein would be useful in limiting
multi-path best-path computation and advertisement to the underlay
routes.
As a second usecase, many times a service provider will carry both
customer traffic and internal services (e.g., VOIP) on the same
backbone network using routes in the same BGP address families. In
this situation, the number of customer routes and paths greatly
exceed the number of routes and paths for internal services.
However, the service provider desires the faster failover and
convergence provided by BGP Add-Paths [I-D.ietf-idr-add-paths]. In
this scenario, the Selective Add-Path functionality described herein
can be leveraged for routes corresponding to internal services
without the overhead incurred if multiple paths were advertised for
the customer routes.
5. IANA Considerations
This document defines a new capability for BGP. We request IANA to
assign BGP capability number from BGP Capabilities Registry.
This document also defines a new extended community for BGP. We
request IANA to assign a BGP well-known extended community from the
Transitive Opaque Extended Community Sub-Types Registry.
6. Security Considerations
This extension to BGP does not change the underlying security issues
inherent in the existing [RFC4724] and [RFC4271].
6.1. Acknowledgements
The authors would like to thank .... for the review and comments.
7. References
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7.1. Normative References
[I-D.ietf-idr-add-paths]
Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", draft-ietf-idr-
add-paths-13 (work in progress), December 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <http://www.rfc-editor.org/info/rfc5492>.
7.2. Information References
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<http://www.rfc-editor.org/info/rfc4456>.
[RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
DOI 10.17487/RFC4724, January 2007,
<http://www.rfc-editor.org/info/rfc4724>.
Authors' Addresses
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: keyupate@cisco.com
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Acee Lindem
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: acee@cisco.com
Luay Jalil
Verizon
400 International Parkway
Richardson, Tx 75081
USA
Email: luay.jalil@verizon.com
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