It's frustrating when you are a tech writer and you can't figure out why things just aren't working right with a network. It's gratifying when you find the one setting you need to change to get everything working again.
A few months ago, I had purchased a new Apple AirPort Extreme because the old one was dropping network connections on an increasingly more frequent basis. The APE was easy to set up and everything was fine... or so I thought. Then during the past months I started running into a lot of issues -- none of my computers could find my third-generation Apple TV, I had problems with home automation devices, and a brand-new Wi-FI speaker wouldn't accept streaming music.
Of course, since the AirPort Extreme was providing much faster access to the Internet than I had ever experienced before, I didn't think it was the problem. I kept thinking that it was the Apple TV (well, it would have been a good excuse to get the fourth-generation model) and a crappy parade of home automation devices. But that issue with the speaker (which I'll review soon) really had me bugged.
Sometimes it's possible to find the answer to a problem when you ask the right question, and that's what fixed the problem this time. I found one article during a search that pointed to a mixup in IPv6 and IPv4 routing on the AirPort Extreme as a probable cause of not being able to use AirPlay. Sure enough, I went into the AirPort Utility on my iPhone (the same app on my iMac couldn't even see the AirPort Extreme!), disabled "Share IPv6 Connection" and after the router rebooted, everything started working properly again.
The images below show the setting disabled on both iOS and OS X. To get to the setting with the iOS AirPort Utility app, tap Edit > Advanced > IPv6 and then tap the Share IPv6 Connection button to disable IPv6 sharing.
For OS X, launch the AirPort Utility (found in Applications > Utilities), click on the AirPort, click Edit, click the Internet tab, then click Internet Options. Find the Enable IPv6 Connection Sharing check box (see below) and uncheck it.
It's sure nice to have everything in the house working together again!