DNS unreachable in new CUCM

[gvitadmin]

i am migrating my CUCM from version 9.xx to 12.xx.

while setting up the new CUCM, there is this warning on upon first login.

Warning: DNS unreachable.

have tested that cucm server can ping my DNS server.

DNS record is already updated on my DNS server.

what else i need to do 

[TONY SMITH]

The "DNS unreachable" message can show if reverse lookup fails, if there's no PTR record. Quick test from a PC use "nslookup" to look up the IP address of the CUCM server.