Operation Manual – Routing Protocol
H3C S5600 Series Ethernet Switches
Chapter 5 BGP Configuration
5-16
MP-BGP is backward compatible. It enables communications to routers with BGP-4
employed.
II. Extended attribute of MP-BGP
Of different types of BGP-4 packets, all the information concerning to IPv4 are carried
by Update packets. The information is hold by NLRI, NEXT_HOP (in the AS_PATH
attribute), and AGGREGATOR (in the AS_PATH attribute). (The AGGREGATOR
attribute contains the IP address of the BGP speaker that generates a summarized
route.)
To support multiple network layer protocols, NLRI and NEXT_HOP need to hold the
information about the network layers. To achieve this, the following two path-related
attributes are added in MP-BGP.
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MP_REACH_NLRI, which stands for multiprotocol reachable NLRI and is used
to advertise reachable routes and next hop information.
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MP_UNREACH_NLRI, which stands for multiprotocol unreachable NLRI and is
used to withdraw unreachable routes.
The two attributes are all of the optional non-transitive type. Therefore, BGP speakers
that do not support multiple protocols ignore the information carried in the two
attributes and do not pass the information to their neighbors.
5.1.6 Protocol Standard
Protocol standards concerning BGP are:
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RFC1771: A border gateway protocol 4 (BGP-4)
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RFC2858: Multiprotocol extensions for BGP-4
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RFC3392: Capabilities advertisement with BGP-4
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RFC2918: Route refresh capability for BGP-4
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RFC2439: BGP route flap damping
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RFC1997: BGP communities attribute
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RFC2796: BGP route reflection
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RFC3065: Autonomous system confederations for BGP
Others are still in draft, such as the graceful restart feature and the extended
COMMUNITY attribute.