System information

BSR 64000 Configuration and Management Guide
12-4
BGP Peers
BGP provides a means for BGP peers, or neighbors, to exchange routing information
within an AS (IBGP) and with peers within other ASs (EBGP). Information is
exchanged between peers about the following:
• New active routes and their attributes
• Inactive routes
• Unusual conditions that require connection termination
BGP does not require routing information to be refreshed. Advertised route
information is considered valid by its neighbors until the first router explicitly
advertises that the information is no longer valid or until the BGP session is lost.
BGP Updates
BGP routers exchange routing information in the form of BGP updates. BGP updates
contain the following attributes associated with routes that a BGP peer advertises to
its neighbors:
• A list of ASs the routing update passed through
• The AS routing update origin
• Next hop information
• Metrics specifying route preference
BGP Sessions
After exchanging a series of messages, the BGP peers establish a session over TCP.
BGP session partners rely on TCP to manage the underlying connection. Once a TCP
connection is established, a BGP router uses port 179 to communicate full routing
information with another BGP peer. As long as the connection is up, the BGP partners
can exchange a very simple set of messages with minimal overhead.
The BGP protocol includes the exchange of keep-alive messages between peers. A
keep-alive message is a signal from one endpoint to another, indicating that the first
end point is still active. Keep-alive messages are necessary to keep BGP peers aware
of the health of the connection, because TCP does not provide this service.