Extend a network with Airport Time Capsule

It's pretty simple. Whenever an AirPort router connects to a network using an Ethernet connection, the AirPort must be configured to "Create a wireless network".......no matter whether the AirPort is connecting to another Apple router or a third party router.

If the AirPort connects using Ethernet......and.....the AirPort is incorrectly configured to "Extend a wireless network", that will set up a huge feedback loop that will crash the network......no matter whether the AirPort is connecting to another Apple router or a third party router.

The only time that the "Extend a wireless network" setting would be used would be if an AirPort router connects to another AirPort router using only a wireless connection.....and......the user does not mind losing half of the potential speed on the network, which will always occur when a network is extended using a wireless connection.

If you use Apple's AirPort Utility setup "wizard", the application will scan the network and automatically suggest the correct setup for the situation at hand.

Technically speaking, when all of the routers connect to a network using an Ethernet connection and broadcast the same SSID using the same password, this is called a "roaming network".

my question is, on the TC, should I set it up to extend a network?

No, the TC must be set up to "Create a wireless network". Simply change the name of the SSID and password on the TC to match the SSID and WiFi password of the new gateway.

"Extend a wireless network" is a setting that would be used only if the TC was connecting to another Apple Airport router using a wireless connection, not an Ethernet connection.

Your next question might be can the TC connect to the Xfinity or Arris gateway using a wireless connection and extend the network in that manner. The answer is no, since Apple designed their "extend" setting as a proprietary feature that will only work with other Apple AirPort routers.

Happy to help. Good luck!