[166349] in North American Network Operators' Group
Re: clear forwarding route
daemon@ATHENA.MIT.EDU (Blake Hudson)
Fri Oct 18 17:22:03 2013
Date: Fri, 18 Oct 2013 16:21:55 -0500
From: Blake Hudson <blake@ispn.net>
To: nanog@nanog.org
In-Reply-To: <CAG1kdogOyEVeKhhDm3oOsvuHiJEnCEz=uYWjZY+DwKvKpzBLeg@mail.gmail.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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
