RFC 2858 (rfc2858) - Page 2 of 11


Multiprotocol Extensions for BGP-4



Alternative Format: Original Text Document



RFC 2858           Multiprotocol Extensions for BGP-4          June 2000


   associated a particular Network Layer protocol with NLRI. To identify
   individual Network Layer protocols this document uses Address Family,
   as defined in [RFC 1700].

   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. 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








Bates, et al.               Standards Track