BGP requires that IBGP peers be fully meshed, creating significant routing overhead as the number of peers increases. The number of IBGP sessions increases rapidly with the number of routers:
For example, in an AS with 9 BGP peers, the peers can conduct 36 sessions:
BGP provides the following two alternative configuration strategies to reduce the number of fully meshed peers:
Both of these strategies are complex and can create their own problems. Neither strategy is typically used unless the mesh of IBGP peers approaches 100 sessions per peer.
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