Cisco IP Phone 6851

Check DHCP Settings
Procedure
Step 1
On the phone, press Applications .
Step 2
Select Admin Settings > Network Setup > IPv4 Setup.
Step 3
Check the DHCP server field.
Check the DHCP option for enabled or disabled.
Step 4
Check the IP Address, Subnet Mask, and Default Router fields.
If you assign a static IP address to the phone, you must manually enter settings for these options.
Step 5
If you are using DHCP, check the IP addresses that your DHCP server distributes.
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 6800 Series Multiplatform Phones Administration Guide
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Additional Troubleshooting Information