IP Routes Based on BGP Best Paths

Some of the complexity related to BGP occurs around the BGP functions created by BGP PAs, including their use by the best-path algorithm. When the BGP best-path algorithm has gotten through this complexity and chosen a best route for a prefix, the router then tries to add that route to the IP routing table. However, rather than add the BGP route to the IP routing table directly, BGP actually gives that best BGP route to another process for consideration: the Cisco IOS Routing Table Manager (RTM).

The Cisco IOS RTM chooses the best route among many competing sources. For example, routes can be learned by an IGP, BGP, or even as connected or static routes. Cisco IOS collects the best such route for each prefix ...

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