This is a hack that most vendors provide, just in case their code doesnt work as expected. Nobody in his sane mind will clear the FIB on a live router. This creates all sorts of problems. The router starts sending out ICMP errors (unreachables, etc), BFD times out, causing all hell to break lose within the domain. It might make some sense to do this on flow based routers where you clear the FIB so that newer flows can get established in case there are hash collisions or issues in flow caches. Even in that case its an issue as all live traffic starts hitting SW before the flow can get established. Customers, you can rest assured, will not appreciate you doing this. And its precisely for this that you never ever do this on a live router. On Friday, 18 October 2013, 21:31, Manav Bhatia <manavbhatia@gmail.com> wrote: 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