H3C LS-3100-52P-OVS-H3 Operation Manual - page 678
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4) After the restart is completed, the GR Restarter will reestablish GR sessions with its peers and
send a new GR message notifying the completion of restart. Routing information is exchanged
between them for the GR Restarter to create a new routing table and forwarding table and have
stale routing information removed. Then the BGP routing convergence is complete.
MP-BGP
Overview
BGP-4 supports IPv4 unicasts, but does not support 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) in RFC 4760.
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 address format, namely NLRI, NEXT_HOP and
AGGREGATOR (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:
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MP_REACH_NLRI: Multiprotocol Reachable NLRI, for advertising feasible routes and next hops
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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 and do not forward them to its peers.
Address family
MP-BGP uses address families 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 and IPv6 extension. Different extensions are configured in respective address
family view.
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For information about the VPN extension application, refer to MCE Configuration in the IP Routing
Volume.
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For information about the IPv6 extension application, refer to IPv6 BGP Configuration in the IP
Routing Volume.
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This chapter gives no detailed commands related to any specific extension application in MP-BGP
address family view.
Protocols and Standards
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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