Xfinity router uses IP address as a default IP for identification on the network. When you receive Xfinity router and you or service technician installs it on the network it will connect to the network using IP. It is possible that technician will change it to a different IP during install but this is not typical. If is used then Xfinity router will assign addresses from to to devices on the network via DHCP protocol. Network mask will be used.

Following routers use IP address as their default:

Xfinity Comcast Router and Gateway
Alfa AP51 router
Aztech NA8300 router
Cisco DPC3941 router
Cisco DPC3939 router
Lucent AS-2000 router
Netcomm N3G9W router
Cisco AIR-AP342E2CUS router
Aris TG1682G router
Cisco 881-W router

To setup your router type in its administration IP address into your browser address bar and press enter. If you do not see your router administration interface check if you are using correct IP address.