176 | Border Gateway Protocol
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Since each BGP router talking to another router is a session, a BGP network needs to be in “full mesh”.
This is a topology that has every router directly connected to every other router. Each BGP router within an
AS must have iBGP sessions with all other BGP routers in the AS. For example, a BGP network within an
AS needs to be in “full mesh.” As seen in Figure 9-2, four routers connected in a full mesh have three peers
each, six routers have 5 peers each, and eight routers in full mesh will have seven peers each.
Figure 9-2. Full Mesh Examples
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.
4 Routers
6 Routers
8 Routers
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