Yosemite network connection issue

[neilf]

Running a 2012 Mac Mini with ethernet connection. Just logged on, and it's telling me my IP address is being used by another device. Never ever had that issue with Mavericks.
We have a Macbook Pro which was being used wirelessly without issues. It is also running Yosemite.
Why would the Mac Mini suddenly decide not to use the ethernet connection, and try to connect to an already used wi-fi IP address?
Any ideas welcome, or has anyone seen this before?

 

[fwfire]

Yosemite connection issues

Having the same ethernet connection issues on my late 2009 mac mini after installing Yosemite. Apparently LOTS of other people are too and Apple's response so far is stone cold silence. Not even an acknowledgment of the widespread problem that's crippling ethernet and wifi connections across a broad spectrum of hardware configurations. Frustrating!

 

[MacInWin]

OK that was two problems.

For the duplicate iP, restart your router. It hands out the iP numbers, so it's handed out the same one to two devices. Not a Yosemite problem, but shows up because you connected.

As for the priority of networks, go to System Settings, Network, and then in the right hand window you'll see all the ways the Mini can connect. If you don't want to use WiFi, then select WiFi and click on the "-" at the bottom of the column. Or you can just turn off WiFi on the top bar to kill the connection.

BTW, the duplicate IP numbers MAY be caused by your system shifting between the two network interfaces (WiFi and Ethernet) because you have both activated and plugged in. The OS tries to sort out what you want, but cannot. What SHOULD happen is that WiFi has one IP and Ethernet has a second one, which is confusing to the Mini, but it could have gotten the same IP at both interfaces, but to the router looks like two different machines. Just turn off the WiFi and if that was the cause, it will go away.

BTW, it's not Yosemite. I've seen the same thing in Snow Leopard on, and on Windows since XP. Ubuntu does it too. Double connections are tricky unless you specifically account for it with tweaks to the internals of the OS, which most folks don't need or do.

 

[fwfire]

Yosemite wifi/ethernet

Thank you for the speedy reply. I had already tried unplugging the router a couple of different times to reset. That works for awhile, but eventually the connection on the mini always reverts back to the duplicate IP issue. As for the ethernet issue, I've always disabled the wifi when trying to use the ethernet connection. I did try your suggestion of deleting the wifi altogether. But that didn't help either. I have been able to use the ethernet for a few short periods. But then a problem always develops causing a disconnect. Although ethernet doesn't work, it does show to be connected as long as my wifi is selected in "location" (with wifi disabled as I mentioned). When I switch to "automatic" the ethernet connection is lost. If this duplicate IP issue isn't related to the recent Yosemite installation, I'm just curious why I never had the problem while running Mavericks.

Thanks again for your help

 

[dtravis7]

Jakes info is Spot on.

Do you have anything else on your network like your phone or a tablet or some other device? Also is your WiFi using WPA2 with a good key?

Is your Wife's Mac on the net when this happens?

 

[fwfire]

Wifi is using WPA2 authentication. And yes I have an iPhone, iPad and a macbook pro on the network. At times, all 4 devices are active at the same time. But the mini seems to be the one primarily affected by losing connection. My wife also has an iPhone and an iPad but the problem has occurred when her devices aren't logged on.

With wifi turned on (but not working): If I unplug my ethernet cable, a wifi connection suddenly pops back up on the mini. This supports Jake's point of wifi and ethernet competing with each other for a connection. But what I'd like to do is use ethernet while leaving wifi turned off. Unfortunately, when I try that configuration, I have internet for only a brief period. In other words, I may get one page to load successfully via ethernet, followed by a shut down of the connection.