Multiprotocol Extensions for BGP-4
RFC 4760
Document | Type |
RFC - Draft Standard
(January 2007; Errata)
Updated by RFC 7606
Obsoletes RFC 2858
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Authors | Tony Bates , Ravi Chandra , Yakov Rekhter , Dave Katz | ||
Last updated | 2020-01-21 | ||
Stream | Internent Engineering Task Force (IETF) | ||
Formats | plain text html pdf htmlized (tools) htmlized with errata bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4760 (Draft Standard) | |
Action Holders |
(None)
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Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Bill Fenner | ||
Send notices to | (None) |
Network Working Group T. Bates Request for Comments: 4760 Cisco Systems Obsoletes: 2858 R. Chandra Category: Standards Track Sonoa Systems D. Katz Y. Rekhter Juniper Networks January 2007 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 IETF Trust (2007). Abstract This document defines extensions to BGP-4 to enable it to carry routing information for multiple Network Layer protocols (e.g., IPv6, IPX, L3VPN, etc.). The extensions are backward compatible - a router that supports the extensions can interoperate with a router that doesn't support the extensions. Bates, et al. Standards Track [Page 1] RFC 4760 Multiprotocol Extensions for BGP-4 January 2007 1. Introduction The only three pieces of information carried by BGP-4 [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 associate a particular Network Layer protocol with NLRI. To identify individual Network Layer protocols associated with the next hop information and semantics of NLRI, this document uses a combination of Address Family, as defined in [IANA-AF], and Subsequent Address Family (as described in this document). 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. 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 RFC 2119 [RFC2119]. Bates, et al. Standards Track [Page 2] RFC 4760 Multiprotocol Extensions for BGP-4 January 2007 3. 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. The attribute is encoded as shown below:Show full document text