But wait, there's more
You still have one more very important step. Normally, when you set up any router, you connect it to the Internet through the WAN (Wide Area Network) port. It tells the device that this is the source you should be using to distribute IP addresses to all the devices you're serving. But our Wi-Fi device isn't "serving" anything anymore. It's simply passing the connection from the remote devices to the base station. So instead, connect an Ethernet cable from your AirPort Extreme Base Station to the LAN (Local Area Network) port of your Wi-Fi device. That tells your Wi-Fi device that it's nothing special--just another device on the base station's network. An ego-deflating message for your Wi-Fi device, perhaps, but it will make for a much happier network.
Click Save on your Wi-Fi device's configuration page, click OK to let it reboot and voila--you've got a thoroughly modern, super speedy network that still has all the ease of use of your comfy old base station.
There are a couple of things to note with this kind of setup. Because your Wi-Fi device is now just a peer on your network, external drives and printers connected to its USB ports won't be seen by other devices. On the plus side, the device will act as a network switch, so you can hard wire other devices to it via its remaining LAN ports. You'll just need to leave the WAN port empty.
If you're willing to do a little more configuring at the beginning, a combo setup like this can give your network extra speed, a few more Ethernet ports, and a lot more flexibility. The fact that it can also save you money doesn't hurt either.
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