196
NOTE:
After route reflection is disabled between clients, routes can still be reflected between a client and a
non-client.
Confederation
Confederation is another method to manage growing IBGP connections in ASs. This method splits an AS
into multiple sub-ASs. In each sub-AS, IBGP peers are fully meshed, and, as shown in
,
intra-confederation EBGP connections are established between sub-ASs.
Figure 85
Confederation network diagram
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
AS 100
EBGP
IBGP
IBGP
IBGP
EBGP
EBGP
AS 65002
AS 65003
AS 65004
AS 200
