Cisco IP Phone 7800 Series Manual page 7

Note: In this example, the IP address is 192.168.100.116.
Step 6. Enter the subnet mask in the Subnet mask field.
Note: In this example, the subnet mask is 255.255.255.0.
Step 7. Enter the gateway address in the Gateway address field.
Note: In this example, the gateway address used is 192.168.100.1.
Step 8. Enter the primary DNS address in the DNS 1 field.