Need to extend wifi provided by Xfinity

Once you decide on a location for the AirPort Extreme, the Extreme will need to connect back to the Xfinity router using a permanent, wired Ethernet cable connection in order to extend the Xfinity network.

Connect the Ethernet cable from one of the LAN <-> ports on the Xfinity router to the WAN "O" port on the AirPort Extreme.

Configure the AirPort Extreme to create a wireless network using the same wireless network name, same wireless security settings and same wireless network password as the Xfinity router.

The final configuration step is to insure that the AirPort Extreme is configured to operate in Bridge Mode, so that it will work with the network correctly.

Connect your Extreme to the Xfinity device with an Ethernet cable, and use another AirPort Base Station to "wirelessly extend" its network.

Read: Wi-Fi base stations: Extending the range of your wireless network by adding additional Wi-Fi base stations

An Apple AirPort Base Station can only "wirelessly extend" a network created by another Apple AirPort Base Station.

I also just recieved an upgraded router from Xfinity, with a built in WiFi network. Question is, can I extend the Xfinity wifi network using my airport Extreme, rather than connecting it via eithernet thus creating a second WiFi network?

The option in the setup utility to use the Airport to extend an existing network doesnt work.

can I extend the Xfinity wifi network using my airport Extreme, rather than connecting it via eithernet thus creating a second WiFi network?

Sorry, but no. The AirPort Extreme can only wirelessly extend if it connects to another Apple wireless router. It is not compatible for that purpose with an Xfinity product.

If you are able to connect the AirPort to the Xfinity router using a permanent Ethernet connection, then you can use the AirPort to "create" a network using the exact same wireless network name and password as the Xfinity network......which will, in effect, "extend" the Xfinity network. So, you will have one "big" network.

Note that you can also simplify this process by renaming the xfinity network to the same name as your existing network. Here are the steps on how to do this (from this website http://forums.comcast.com/t5/Home-Networking-Router-WiFi/Can-i-change-my-wifi-na me-and-password/td-p/1258033

• Log into the router at http://10.0.01 (assuming it is using the default address). The default userid is "admin", the default password is "password".
• You should be presented with a wizard setup as described on page 8 in your manual.
• If you are NOT presented with the wizard, you will have to go make the changes directly...
• Go to Gateway -> Connection -> WiFi and press the EDIT button next to your wireless network.
• Change the Network Name (SSID) and the Network Password to whatever you desire and then press the SAVE SETTINGS button.
• To change the login password (used in #1 above), go to Troubleshooting -> Change Password, provide the Current Password, the New Password, and Re-enter New Password and press theSAVE button.