Forwarding Information Base (FIB)

Cisco routers build a Forwarding Information Base (FIB) which contains all the routes that could potentially be advertised to all neighboring routers within the next set of announcements. This is also the same set of routes used to forward IP datagrams. On Cisco routers with a distributed forwarding architecture and which have Distributed Cisco Express Forwarding (DCEF) enabled, a copy of the FIB will be 'compiled' and downloaded to the applicable line-cards or modules. This offloads a large portion of the routing load from the main CPU and increases the overall traffic load that can be sustained by the router.