252stale. However, during the configured GR Time, it still uses these routes for packetforwarding.4. After the restart, the GR Restarter will reestablish a GR session with its peer and send a newGR message notifying the completion of restart. Routing information is exchanged betweenthem for the GR Restarter to create a new routing table and forwarding table with stalerouting information removed. Then, the BGP routing convergence is complete.MP-BGPOverviewBGP-4 supports IPv4 unicasts, but does not support other network layer protocols, such as IPv6.To support more network layer protocols, IETF extended BGP-4 by introducing MP-BGP in RFC4760.Routers supporting MP-BGP can communicate with routers not supporting MP-BGP.MP-BGP extended attributesIn BGP-4, the types of attributes for IPv4 address format, namely NLRI, NEXT_HOP, andAGGREGATOR (AGGREGATOR contains the IP address of the speaker generating the summaryroute) are all carried in updates.To support multiple network layer protocols, BGP-4 puts information about network layer into NLRIand NEXT_HOP. MP-BGP introduced the following path attributes:• MP_REACH_NLRI: Multiprotocol Reachable NLRI, for advertising feasible routes and nexthops• MP_UNREACH_NLRI: Multiprotocol Unreachable NLRI, for withdrawing unfeasible routesThe previous two path attributes are both optional non-transitive, so BGP speakers not supportingmultiprotocol ignore these attributes and do not forward them to its peers.Address familyMP-BGP uses address families to differentiate network layer protocols. For address family values,see RFC 1700 (Assigned Numbers), including VPN extension and IPv6 extension. Differentextensions are configured in respective address family view.• For information about the IPv6 extension application, see IPv6 BGP in the Layer 3 – IP RoutingConfiguration Guide.• This chapter provides no detailed commands related to any specific extension application in MP-BGPaddress family view.
