Internet Routing Architectures, Second Edition

Controlling Route and Cache Invalidation

A traditional requirement of BGP was resetting the neighbors' TCP connection in order for a policy change to take effect (clear ip bgp [* | address | peer-group]). Clearing the sessions in this manner restarts the neighbor negotiations from scratch, invalidates the associated portions of the IP forwarding cache, and causes a major impact on the operation of live networks.

The reasoning for this is that, as discussed in Chapter 6, routes learned from a peer are initially populated in the peer's Adj-RIB-In. They are then passed to the Input Policy Engine, modified accordingly, and presented to the BGP decision process. Because an unmodified copy of the route (what was initially stored in the Adj-RIB-In) ...