Figure 18. 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 end-points of that session are Peers. A Peer is
also called a Neighbor.
Establish a Session
Information exchange between peers is driven by events and timers. The focus in BGP is on the trac 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, OpenConrm, and Established. For each peer-to-peer session, a BGP implementation tracks which
of these six states the session is in. The BGP protocol denes the messages that each peer should exchange in order to change the
session from one state to another.
Border Gateway Protocol IPv4 (BGPv4)
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