HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Routing Confi - Page 139

Figure 57 Confederation network diagram AS 65002 AS 65003 EBGP EBGP EBGP AS 100 IBGP AS 200 IBGP IBGP AS 65004 A non-confederation BGP speaker is not required to 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 as follows: • When changing an AS into a confederation, you must reconfigure your routers. • The topology is changed. In large-scale BGP networks, both route reflector and confederation can be used. BGP GR Graceful Restart (GR) ensures the continuity of packet forwarding when BGP restarts or a Master/Slave switchover occurs: • GR Restarter-Graceful restarting router. It must be GR capable. • GR Helper-A neighbor of the GR Restarter. It helps the GR Restarter to complete the GR process. The following describes the BGP routing convergence process: 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 Master/Slave switchover occurs on 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. 129