I've had a route that remained in the RIB (and consequently the FIB) after a BGP session had been disabled or went down (all routes but one were removed correctly). I'm guessing similar bugs exist in other portions of the software, making manual clearing tools a bandaid for these hard to pin down bugs. --Blake Manav Bhatia wrote the following on 10/18/2013 10:40 AM:
Hi,
I would like understand the circumstances under which an operator may want to clear all (or a subset of) the routes programmed in the forwarding table (FIB).
I believe the command to do this on Cisco is
clear forwarding {ipv4 | ipv6} route {* | prefix} [vrf vrf-name] module {slot| all}
I ask this since doing this would result in the router dropping all transit traffic till the routes get reprogrammed in the FIB.
Why would somebody ever want to do this? One scenario that i can think of is when because of a bug a route does not get programmed in the FIB and the operator uses this command to install this once again the FIB.
Thanks, Manav