Can a WAN port be used as a LAN port on a second Airport Extreme?

Yes, if you reconfigure the AirPort Extreme as a bridge ALL ports (WAN or LAN) will become Ethernet ports as it is now performing as an Ethernet switch.

Yep, that's pretty much it. Configured as a bridge, the AEBS would perform, not as a router, but as a combination Ethernet switch & Wireless Access Point. Any network clients connected to it, either by wire or wireless, will get Internet access through it ... and that Internet would be coming from the AirPort upstream of this one.

If you use ethernet to connect the two AirPort Extremes together, you'll have Gigabit speeds available at all of the ethernet ports on both routers.

If you connect the second AirPort Extreme using wireless only and configure the Extreme to "extend a wireless network", then the maximum speeds that the second router can attain will be limited to the capability of the wireless connection. So, if you connect at normal "n" wireless speeds of say 130 Mbps, that will be the maximum speed available at the ethernet ports on the second AirPort Extreme.

I think you can easily see the difference between Gigabit ethernet, which is 1000 Mbps compared to "n" wireless at 130 Mbps. Even if you can manage to connect at 5 GHz speeds for wireless, the max speed will be in the 300 Mbps range, more than 3 times slower than Gigabit ethernet. Normal "n" speeds will be about 7 times slower than ethernet.

For streaming high definition video and other demanding sources, you'll need as much bandwidth (speed) as you can get. Ethernet is always the best choice if you can possibly use it. And...there's no wireless interference on an ethernet connection.

Message was edited by: Bob Timmons

Looks like Bob got you covered. Basically, using wire typically provides better bandwidth over wireless.