Multiprotocol Extensions for BGP-4
RFC 2283
| Document | Type |
RFC - Proposed Standard
(February 1998; No errata)
Obsoleted by RFC 2858
|
|
|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | IETF | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 2283 (Proposed Standard) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
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| Send notices to | (None) | ||
Network Working Group T. Bates
Request for Comments: 2283 Cisco Systems
Category: Standards Track R. Chandra
Cisco Systems
D. Katz
Juniper Networks
Y. Rekhter
Cisco Systems
February 1998
Multiprotocol Extensions for BGP-4
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
2. Abstract
Currently BGP-4 [BGP-4] is capable of carrying routing information
only for IPv4 [IPv4]. This document defines extensions to BGP-4 to
enable it to carry routing information for multiple Network Layer
protocols (e.g., IPv6, IPX, etc...). The extensions are backward
compatible - a router that supports the extensions can interoperate
with a router that doesn't support the extensions.
3. Overview
The only three pieces of information carried by BGP-4 that are IPv4
specific are (a) the NEXT_HOP attribute (expressed as an IPv4
address), (b) AGGREGATOR (contains an IPv4 address), and (c) NLRI
(expressed as IPv4 address prefixes). This document assumes that any
BGP speaker (including the one that supports multiprotocol
capabilities defined in this document) has to have an IPv4 address
(which will be used, among other things, in the AGGREGATOR
attribute). Therefore, to enable BGP-4 to support routing for
multiple Network Layer protocols the only two things that have to be
added to BGP-4 are (a) the ability to associate a particular Network
Layer protocol with the next hop information, and (b) the ability to
associated a particular Network Layer protocol with NLRI. To identify
Bates, et. al. Standards Track [Page 1]
RFC 2283 Multiprotocol Extensions for BGP-4 February 1998
individual Network Layer protocols this document uses Address Family,
as defined in [RFC1700].
One could further observe that the next hop information (the
information provided by the NEXT_HOP attribute) is meaningful (and
necessary) only in conjunction with the advertisements of reachable
destinations - in conjunction with the advertisements of unreachable
destinations (withdrawing routes from service) the next hop
information is meaningless. This suggests that the advertisement of
reachable destinations should be grouped with the advertisement of
the next hop to be used for these destinations, and that the
advertisement of reachable destinations should be segregated from the
advertisement of unreachable destinations.
To provide backward compatibility, as well as to simplify
introduction of the multiprotocol capabilities into BGP-4 this
document uses two new attributes, Multiprotocol Reachable NLRI
(MP_REACH_NLRI), and Multiprotocol Unreachable NLRI
(MP_UNREACH_NLRI). The first one (MP_REACH_NLRI) is used to carry the
set of reachable destinations together with the next hop information
to be used for forwarding to these destinations. The second one
(MP_UNREACH_NLRI) is used to carry the set of unreachable
destinations. Both of these attributes are optional and non-
transitive. This way a BGP speaker that doesn't support the
multiprotocol capabilities will just ignore the information carried
in these attributes, and will not pass it to other BGP speakers.
4. Multiprotocol Reachable NLRI - MP_REACH_NLRI (Type Code 14):
This is an optional non-transitive attribute that can be used for the
following purposes:
(a) to advertise a feasible route to a peer
(b) to permit a router to advertise the Network Layer address of
the router that should be used as the next hop to the destinations
listed in the Network Layer Reachability Information field of the
MP_NLRI attribute.
(c) to allow a given router to report some or all of the
Subnetwork Points of Attachment (SNPAs) that exist within the
local system
The attribute contains one or more triples <Address Family
Information, Next Hop Information, Network Layer Reachability
Information>, where each triple is encoded as shown below:
Bates, et. al. Standards Track [Page 2]
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