[nsp] CEF routing bug?

[Ilker Temir]

> > If arp times out, corresponding /32 CEF adjacency will be removed and
there
> > will be no problem. However arp will never time out in this case (unless
> > remote goes down).
>
> Would clearing the Cisco's ARP table help?  I don't think we tried that
yet.

Probably not. As long as remote continues to reply arp requests it will not
be removed from your arp table (router sends a request following clear arp).
If you temporarily shut the remote and do a clear arp, this would probably
do the trick though ;-)

> Meanwhile, our other CEF problem has nothing to do with ARP.  It
> looks a bit like this:
>
>  Dialup Customer with DSL address
>        |
>        |
>    +---------+             +---------+               +---------+
>    | Router1 |----T3-------| Router2 |-----FastE-----| Router3 |
>    +---------+             +---------+               +---------+
>                                                          |
>                                                          |
>                                                      DSL customer
>
> Our DSL customers are attached to Router3, so we've got a static
> route on Router2 (with a poor metric so it can be overridden by a
> route in the IGP) to direct traffic to the FastEthernet.
>
> When the customer's DSL line is down, they dial in via ISDN, and
> they use the same IP address so that they won't have to reconfigure
> anything.  Router1 redistributes the dialup route via OSPF to
> Router2.  If we have CEF turned on on Router2, it sends traffic
> for that IP to the FastEthernet no matter what's in the routing table.
> If CEF is turned off, the routing table on Router2 is used as expected
> and traffic goes to Router1 for the IP in question.  There's no ARP
> anywhere in the equation here - the DSL customers are at least two
> hops away from Router2.  Router2 is the 7513 with 12.0(21)S1.

There should be a CEF entry remaining, you don't necessarily need ARP for
this. Check the exact destination with 'sh ip cef detail' when you have the
problem.

Ilker


>
> Thanks,
>
> -- Ed
>
> > ----- Original Message -----
> > From: "Ed Ravin" <eravin at panix.com>
> > To: <cisco-nsp at puck.nether.net>
> > Sent: Thursday, January 30, 2003 12:33 AM
> > Subject: [nsp] CEF routing bug?
>
> > > I'm seeing similiar problems on two different routers - a 7206 with
> > > 12.2(7c) and a 7513 with 12.0(21)S1.  On one router, routes received
> > > via OSPF or RIP do not override CEF when the CEF route is on a
> > > FastEthernet interface.  On the other router, the dynamic routes are
> > > used when the router is restarted, but if the dynamic routing
> > > protocol drops the route and CEF takes over, we can't lose the CEF
> > > route without rebooting the router again.
>