Bgp Gr - H3C LS-3100-52P-OVS-H3 Operation Manual

Confederation
Confederation is another method to deal with growing iBGP connections in ASs. It splits an AS into
multiple sub-ASs. In each sub-AS, iBGP peers are fully meshed, and intra-confederation eBGP
connections are established between sub-ASs, as shown below:
Figure 1-15 Confederation network diagram
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

For GR (Graceful Restart) information, refer to GR Configuration in the System Volume.
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 a restart occurs on a 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.
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