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Figure 17. BGP Routers in Full Mesh
The number of BGP speakers each BGP peer must maintain increases exponentially. Network management quickly becomes impossible.
Sessions and Peers
When two routers communicate using the BGP protocol, a BGP session is started. The two endpoints of that session are Peers. A Peer is
also called a Neighbor.
Establish a Session
Events and timers drive information exchange between peers. The focus in BGP is on the trac routing policies.
In order to make decisions in its operations with other BGP peers, a BGP process uses a simple nite state machine that consists of six
states: Idle, Connect, Active, OpenSent, OpenConrm, and Established. For each peer-to-peer session, a BGP implementation tracks which
of these six states the session is in. The BGP protocol denes the messages that each peer should exchange to change the session from
one state to another.
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Border Gateway Protocol IPv4 (BGPv4)