3Com Switch 8800 Advanced Software V5 Configuration Guide

BGP Overview 433
The deficiency of confederation is: when changing an AS into a confederation,
you need to reconfigure your routers, and the topology will be changed.
In large-scale BGP networks, both route reflector and confederation can be used.
MP-BGP Overview
The legacy BGP-4 supports IPv4, but does not support some other network layer
protocols like IPv6.
To support more network layer protocols, IETF extended BGP-4 by introducing
Multiprotocol Extensions for BGP-4 (MP-BGP), which is defined in RFC2858.
Routers supporting MP-BGP can communicate with routers not supporting
MP-BGP.
MP-BGP extended attributes
In BGP-4, the three types of attributes for IPv4, namely NLRI, NEXT_HOP and
AGGREGATOR (contains the IP address of the speaker generating the summary
route) are all carried in updates.
To support multiple network layer protocols, BGP-4 puts information about
network layer into NLRI and NEXT_HOP. MP-BGP introduced two path attributes:
■ MP_REACH_NLRI: Multiprotocol Reachable NLRI, for advertising available
routes and next hops
■ MP_UNREACH_NLRI: Multiprotocol Unreachable NLRI, for withdrawing
unfeasible routes
The above two attributes are both Optional non-transitive, so BGP speakers not
supporting multi-protocol ignore the two attributes, not forwarding them to
peers.
Address family
MP-BGP employs address family to differentiate network layer protocols. For
address family values, refer to RFC 1700 (Assigned Numbers). Currently, the
system supports multiple MP-BGP extensions, including VPN extension, IPv6
extension. Different extensions are configured in respective address family view.
n
■ For information about the IPv6 extension application, refer to “IPv6 BGP
Overview” on page 469.
■ This chapter gives no detailed commands related to any specific extension
application in MP-BGP address family view.
Protocols and Standards RFC1771: A Border Gateway Protocol 4 (BGP-4)
RFC2858: Multiprotocol Extensions for BGP-4
RFC3392: Capabilities Advertisement with BGP-4
RFC2918: Route Refresh Capability for BGP-4
RFC2439: BGP Route Flap Damping