Cisco phone behavior w/o DNS server

[Quintin.Mayo]

Customer would like any documentation or details regarding how their cisco phone system will react to the internal upgrades they are planning. These internal upgrades will require them to power down their domain controller, which is also their DNS server. Customer is unsure how this will affect their phone system.  Any information would be greatly appreciated.

Thanks,

[Roger Kallberg]

If the phones are using DNS to resolve the FQDN of its call processing nodes in the CM cluster they will lose the connection. If the customer is using SRST then the phones will go into survivability mode, otherwise they will have a blackout of the phone services.

[Mohammadreza Hadi]

also you can manually set a bogus DNS on a phone, and see what's happens ?

if nothing >> so phone is not reliance to DNS server..

if goes problem >> you can do 3 options >>
1. setup another backup DNS for downtime scenario, so phones be ok at that time
2. do "remove DNS reliance" scenario on your CUCM.. (which cause all xml config phone filled with ip address of cucm, instead of FQDN of cucm) 
3. do that power down servers in a time like midnight, which no one is using their phones..