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Routing & Switching · Intermediate

BGP Full Mesh

The requirement that every iBGP speaker peer with every other iBGP speaker unless route reflectors or confederations are used.

Definition

Because of iBGP split horizon, routes learned from one iBGP peer are not passed to another, so all must peer directly. n routers need n(n-1)/2 sessions, which scales poorly beyond small networks.

Example

Ten iBGP routers need 45 sessions in a full mesh.

Exam tip

Route reflectors and confederations are the two answers to the iBGP full-mesh scaling problem.

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