Re: Please don't use 11.1-MFIB with DVMRP-mode tunnels

[Göran Bengtson <]

On Tue, 31 Mar 1998, David Meyer wrote:

> From: David Meyer dmm@localhost
> To: fenner@localhost
>, mbone@localhost
> Message-ID: <199804010050.QAA04830@localhost>
> Date: Tue, 31 Mar 1998 16:50:18 -0800 (PST)
> Subject: Re: Please don't use 11.1-MFIB with DVMRP-mode tunnels
> 
> 
> 	Bill,
> 	
> >>  Please don't use the 11.1-MFIB branch with DVMRP-mode tunnels.
> >> There is a bug (which Cisco knows about and is working on) which
> >> can cause DVMRP-mode tunnels to black hole all traffic flowing
> >> through them.
> 
> 	The basic problem is that when a downstream neighbor poisoned 
> 	the cisco, the tunnel didn't get put into the OLIST for the 
> 	(for that (S,G)). On inspection, it turns out that this
> 	occurs only when ip dvmrp unicast-routing is configured on
> 	a dvmrp tunnel. Turning off 'dvmrp unicast-routing' on the
> 	tunnel solves this problem. We'll harden this up (i.e.,
> 	check for 'ip dvmrp unicast-routing' on a dvmrp tunnel)
> 	so that this doesn't occur again.

I've seen the same problem for 11.3(1 and 2) and it applies to both
tunnels and DVMRP-neighbors on LANs. On LANs the work-around may not
be feasible since 'dvmrp unicast-routing' may be needed for RPF-checks.

> 
> 	Dave

		/ Göran Bengtson, Chalmers Univ. of Technology