Tom has four iMacs and each one is getting an error when connecting to ethernet, and can't connect to the Internet because of a "self-assigned address." But he can connect via WiFi. Leo says to go to the Network system preference pane and make sure that Ethernet is dragged to the top. Also, make sure it's using DHCP in the settings. One thing that may be causing the error is that the computer doesn't see the ethernet cable when booting up, and then gives the self-assigned address. It could also be the router itself.
Ray is having trouble streaming. It buffers a lot. Leo says that if his router is a few years old, it could slow down and become less reliable. Rebooting the router will bring it back, but then it'll happen again. So he should get a new one. His TV's Wi-Fi may also be getting "promiscuous," meaning it is jumping to a stronger signal every time it finds one. He can also go into his router and adjust the "lease time for DHCP" to make it longer before it acquires a new IP address. He can also get a dual band router, which will have 2.4 GHz and 5.0 GHz.
Mike's XBox One is losing its Wi-Fi connection after about an hour. It won't even work with a hard wire. Leo says it could be a bad Wi-Fi radio, but that wouldn't have anything to do with the ethernet chip. There could be an issue with the DHCP host protocol. DHCP assigns IP addresses and they are dynamic, so they can expire.
Chris bought a fourth Airport Express, but now the wireless client is broadcasting the Wi-Fi information by numbers, not names. So he has no clue what devices are what. He says it happened after upgrading the software. Leo says that's baffling, but he has a hunch it's the device's MAC addresses.