This is a post for dummies, like myself, so apologize my non-tech language
I had the self-assigned IP problem for a week and tried all possible
easy fixes:
-Reboot modem and devices (twice, sounds like voodoo to me)
-Opened system preferences/network/advanced/TCP/IP clicked renew DHCP license -->this would allow sometime one device to connect, but not all devices at once
-Opened system preferences/network/advanced/TCP/IP and under configure IPv6 clicked link-local only (same results as above)
-Even ruled out "interferences" setting up a 5.2 Ghz network (sorry if I'm using the wrong words, like I said, I'm quite ignorant about this)
Nothing worked.
My set up was a modem, three powerline extenders that connected via ethernet to 1) an airport express, 2) an i-mac, 3) an apple TV (if you have no idea what a powerline is read side note below on powerlines)
I finally understood what
the problem was: I could only connect one device at the time, meaning that if I restarted the modem with only one device connected that device would work. If I had two or more connected the remaining devices had a self-assigned IPs.
Now
for you dummies-like-me out there (I apologize to all techies out there for using wrong words, concepts etc... the modem receives internet from provider and gives it to your home. Internet works in numbers (IP addresses) that tell your modem what devices are connected to it. Now, modems tpically, can connect to one thing at the time. To connect multiple devices you need a router. The router looks exactly like a modem to me (ha ha) it's another little black box, but it will have multiple ethernet ports on its back. Airport express can work as routers (theoretically, as it turned out mine wasn't). The router generates a range of IP addresses, for example, if you are using your airport express as a router you can see the range under system preferences/network/advanced/TCP/IP it could be 10.10.00.01 to 10.10.00.200 (probably not, maybe this is an impossible range, like I said, dummy here, but it will look something like this to other dummies out there). Now, if that is your range and your devices have an IP address of 169.225.xxx.xxx you have a problem. Your device has an IP address not in the range determined by your router= you have no internet. To find the IP address of your device: on a mac system preferences/network/advanced/TCP/IP (I think it's the IPv4 address... maybe and it should have the first bunch of numbers identical to your router or within the range determined by your airport express) on my apple TV it was under settings/general/connection
The problem: I finally determined that the problem was that my airport express, for some reason, could only assign one IP address at the time. If all 3 devices were connected, only one would get a valid IP address. Basically, it was not doing its router job. Apple support were sweet as pie but useless and told me it was a problem due to my provider (which wasn't).
The fix: I plugged my modem into an old router I had lying around in the house from my pre-airport express days, restarted the modem and everything went back to normal I almost cried for joy.
My current set up:
1-cable from provider into modem
2-ethernet cable from modem into router (into the internet port, not one of the numbered ethernet ports)
3-ethernet cable from one of the numbered ports of the router into ethernet port of powerline extender, plugged into a wall
4a-2nd powerline extender plugged into a wall on a different floor. Ethernet cable out of that into my airport express to generate wi-fi
4b-3rd powerline into a different wall plug. Ethernet from that to i-mac
4c-4th powerline into different plug connected through ethernet to my apple TV
I hope this helps!
Side note on powerline extenders: I live in a big old house with thick walls and wi-fi won't reach everywhere. Powerline extenders are magic portals that allow your internet to travel through walls (ha ha). I have TP-LINK (TP-link TL-PA511 KIT AV500 Powerline Gigabit Adapter Starter Kit, up to 500Mbps). They're $60 a pair on amazon. The way they work: plug an ethernet cable from your router into the powerline, plugged into the wall (they have to be plugged into the wall to work!). Plug another powerline anywhere into your house (within a ridiculous distance, maybe 300 meters/yards or so) and internet will come out of that precious little thing at the same speed it came out of your modem=magic.
Side note on airport express: I think my airport express is glitchy but that said, I used airport utility to set it up. How? On a mac just look for airport utility (apple key+ space to open the search tab). From there click on wi-fi. If the utility does not see your airport express reset it with a pen, clicking that little spot that can only be pushed with a pen till the yellow light pulses fast a few times. For me, sometimes, it takes a couple of clickings to get there. Then wait. On the utility after a while if you click on "other wi-fi devices" on the up-left corner you'll see a number in the scrolldown menu: that's your reset airport express. Select it. Set it to create a wi-fi network (if that's what you need) name the network, assign a password and you should be all set.
