16-14 Riverstone Networks RS Switch Router User Guide Release 8.0
BGP Configuration Examples
BGP Configuration Guide
•
BGP accounting
16.3.1
BGP Peering Session Example
The router process used for a specific BGP peering session is known as a
BGP speaker
. A single router can have several
BGP speakers. Successful BGP peering depends on the establishment of a neighbor relationship between BGP
speakers. The first step in creating 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.
Note
To request route database refreshes from peer-hosts, first add
bgp set
peer-host/peer-group route refresh
to the active configuration. Then,
use the
bgp clear peer-host soft-inbound
command. The
soft-inbound
option causes the peer-host to re-send it routing information
without breaking and then reestablishing the connection to the peer-host.
BGP “keepalive” messages are sent between peers periodically to ensure that the peers stay connected. If one of the
routers encounters a fatal error condition, a BGP notification message is sent to its BGP peer, and the TCP connection
is closed.
Figure 16-2
illustrates a sample BGP peering session:
