CUCM/SRST - Phones failover to SRST but don't failback

[jason.henderson]

I have an issue where a remote office that registers with a CUCM over an MPLS link - the MPLS failed and the phones successfully failed over to their local SRST router.  The MPLS was down for a period of time, so the site was reconfigured with a L2L VPN so that it could reach CUCM again.  However, the phones didn't failback to CUCM.  After an hour or so, they were rebooted and re-registered with CUCM fine.

Does anyone know what could have caused this issue?  Happy to provide any more info if necessary.

Thanks in advance,

Jason

[acampbell]

Jason,

I think the explanation to your issue is ARP caches on the IP phones

Your phones would have the MAC of your failing MPLS linked router against that routers IP address.

If you have moved the IP address to another router the phones will not know about this until their ARP caches are reset.

As far as I know the Cisco IP phones have a long ARP cache timer, in hours rather than a few seconds or minutes like a PC.

So resetting the phones will have forced them to renew their ARP caches to include the new VPN router.

HTH

Alex