See the
Understanding and Troubleshooting DHCP in Catalyst Switch or Enterprise Networks
document,
available at this URL:
https://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a00800f0804.shtml
Verify DNS Settings
Procedure
Step 1
On the phone, press
Applications
.
Step 2
Select
Admin Settings
>
Network Setup
>
IPv4 Setup
Step 3
Check that the DNS Server 1 field is set correctly.
Step 4
You should also verify that a CNAME entry was made in the DNS server for the TFTP server and for the
Third-Party Call Control.
You must also ensure that DNS is configured to do reverse lookups.
Additional Troubleshooting Information
If you have additional questions about troubleshooting your phone, go to the following Cisco website and
navigate to the desired phone model:
https://www.cisco.com/cisco/web/psa/troubleshoot.html
Cisco IP Phone 7800 Series Multiplatform Phones Administration Guide
318
Cisco IP Phone Troubleshooting
Verify DNS Settings