IP Phone DNS Cache

[ReeganDeacon85538]

Hi there, sorry if this has been answered I was not able to find exactly what I was looking for.

We have a single CUCM cluster on version 12.5 with the servers defined by FQDN in system > server.

• 7800 and 8800 phones.

I was curious if we have an outage with our central primary/backup DNS servers, how long will the IP phones cache the record for the CUCM server to continue to stay registered ?

• If the specified TTL expires on the cached record for the phone will it unregister?

Thanks!

[ReeganDeacon85538]

Anyone ? or any other details I can provide ?

[Ayodeji Okanlawon]

The phone will use the TTL value to expire it's cache entry after which it will try to contact DNS again. If there is a DNS outage, from experience the phone will continue to use its old entry. Phones are a little stubborn and don't give up their configuration easily..