H3C Technologies H3C S12500 Series Switches - Manual (Page 218)

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In large-scale BGP networks, both route reflector and confederation can be used.
MP-BGP
BGP-4 transmits IPv4 unicast routes, but does not transmit routing information of other network layer
protocols, such as IPv6.
To support more network layer protocols, IETF extended BGP-4 by introducing Multiprotocol Extensions
for BGP-4 (MP-BGP). MP-BGP can transmit routing information of various network layer protocols, for
example, IPv4 multicasts, IPv6 unicasts, IPv6 multicasts, and VPNv4 routes.
Routers supporting MP-BGP can communicate with routers not supporting MP-BGP.
MP-BGP extended attributes
Prefixes and next hops are key routing information of network layer protocols. In BGP-4, each update
message can carry prefixes of feasible routes in the Network Layer Reachability Information (NLRI) field,
prefixes of unfeasible routes in the withdrawn routes field, and next hops in the NEXT_HOP attribute. The
NLRI field, withdrawn routes field, and NEXT_HOP attribute cannot be extended to carry information of
multiple network layer protocols.
To support multiple network layer protocols, MP-BGP defines the following path attributes:
• MP_REACH_NLRI—Multiprotocol Reachable NLRI, for carrying prefixes of feasible routes and next
hops for multiple network layer protocols. Such routes can then be advertised.
• MP_UNREACH_NLRI—Multiprotocol Unreachable NLRI, for carrying prefixes of unfeasible routes
for multiple network layer protocols. Such routes can then be withdrawn.
MP-BGP uses these attributes to advertise feasible and unfeasible routes of different network layer
protocols. BGP speakers not supporting MP-BGP ignore updates containing these attributes and do not
forward them to its peers.
The system supports multiple MP-BGP extensions, including VPN extension (see MPLS Configuration
Guide), IPv6 extension (see "Configuring IPv6 BGP"), and multicast extension (see see IP Multicast
Configuration Guide).
Address family
MP-BGP uses address families and subsequent address families to differentiate network layer protocols of
routes contained in the MP_REACH_NLRI and MP_UNREACH_NLRI attributes. For example, an Address
Family Identifier (AFI) of 2 and Subsequent Address Family Identifier (SAFI) of 1 indicates IPv6 unicast
routing information carried in the MP_REACH_NLRI attribute. For address family values, see RFC 1700.
BGP configuration views
Table 7 shows views for different address families supported by BGP. This chapter describes
configurations in BGP view and BGP-VPN view.