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SmartSwitch Router User Reference Manual 79
Chapter 6: BGP Configuration Guide
a BGP neighbor relationship is the establishment of a TCP connection (using TCP port
179) between peers.
A BGP Open message can then be sent between peers across the TCP connection to
establish various BGP variables (BGP Version, AS number (ASN), hold time, BGP
identifier, and optional parameters). Upon successful completion of the BGP Open
negotiations, BGP Update messages containing the BGP routing table can be sent between
peers.
BGP does not require a periodic refresh of the entire BGP routing table between peers.
Only incremental routing changes are exchanged. Therefore, each BGP speaker is required
to retain the entire BGP routing table of their peer for the duration of the peer’s
connection.
BGP “keepalive” messages are sent between peers periodically to ensure that the peers
stay connected. If one of the routers encounter a fatal error condition, a BGP notification
message is sent to its BGP peer and the TCP connection is closed.
Figure 2 illustrates a sample BGP peering session.
Figure 2. Sample BGP Peering Session
Physical Link
Legend:
Peering Relationship
AS-2
SSR1
10.0.0.2/16
10.0.0.1/16
SSR2
AS-1
1.1
1.1