Cisco FIB VS RIB

Routing Information Base (RIB)

The Routing Information Base RIB is the location in which all IP Routing information is stored. The RIB is not specific to any routing protocol, rather, it is the repository where all the routing protocols place all of their routes. Routes are inserted into the RIB whenever a routing protocol running on the router learns a new route. When a destination becomes unreachable, the route is first marked unusable and later removed from the RIB as per the specifications of the routing protocol they were learned from. It is important to note that the RIB is NOT used for forwarding IP datagrams, nor is it advertised to the rest of the networks to which the router is attached. A Cisco router's RIB will contain filtered routes; however, these will never make it to the "Forwarding Information Base", which contains yet a different set of routes.

 CEF Disabled:

*Mar  1 01:11:40.003: IP: tableid=0, s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), routed via RIB
*Mar  1 01:11:40.003: IP: s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), len 100, sending
*Mar  1 01:11:40.059: IP: tableid=0, s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), routed via RIB
*Mar  1 01:11:40.063: IP: s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), len 100, sending
*Mar  1 01:11:40.087: IP: tableid=0, s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), routed via RIB
 

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.

 CEF Enabled:

*Mar  1 01:11:28.735: IP: tableid=0, s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), routed via FIB
*Mar  1 01:11:28.735: IP: s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), len 100, sending
*Mar  1 01:11:28.755: IP: tableid=0, s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), routed via FIB
*Mar  1 01:11:28.755: IP: s=10.10.10.1 (local), d=192.168.100.1 (FastEthernet0/0), len 100, sending