Bgp; Mp-Bgp - H3C S5800 Series Configuration Manual

From the perspective of a non-confederation BGP speaker, it needs not know sub-ASs in the
confederation. The ID of the confederation is the number of the AS. In the above figure, AS 200 is the
confederation ID.
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.
BGP GR
The S5800&S5820X series switches are centralized devices that support IRF. They can act as a GR
Helper before forming an IRF; they can form a distributed chassis switch in a logical sense and act as
a GR Restarter after forming an IRF. Active and standby switchover in this document refers to the
switching of the master for IRF devices.
Graceful Restart ensures the continuity of packet forwarding when a routing protocol restarts or an
active/standby switchover occurs:
GR Restarter: Graceful restarting router. It must be Graceful Restart capable.
GR Helper: The neighbor of the GR Restarter. It helps the GR Restarter to complete the GR
process.
To prevent service interruption after an active/standby switchover, a GR Restarter running BGP must
complete the following tasks:
1) To establish a BGP session with a peer, a BGP GR Restarter sends an Open message with GR
capability to the peer.
2) Upon receipt of this message, the peer is aware that the sending router is capable of Graceful
Restart, and sends an Open message with GR Capability to the GR Restarter to establish a GR
session. If neither party has the GR capability, the session established between them will not be
GR capable.
3) When an active/standby switchover occurs on a distributed device that acts as the GR Restarter,
sessions on it will go down. Then, GR capable peers will mark all routes associated with the GR
Restarter as stale. However, during the configured GR Time, they still use these routes for packet
forwarding.
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.
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