Ethernet Self-Assigned IP

Question

Level 1

20 points

Ethernet Self-Assigned IP

Hi Folks,

I know it's been discussed ad infinitum over the years but I still haven't found a definitive answer to a common recurring connection problem on my MacPro.

Can anybody explain why after weeks of everything working fine, my Ethernet connection will suddenly drop? I can connect via Wi-Fi, all my other devices are fine. But Ethernet won't connect on the MacPro.

The error given is... Ethernet has a self-assigned IP address and will not be able to connect to the internet.

I then switch to Wi-Fi and use that instead. After about 10 minutes, the Ethernet connection mysteriously pops back into action.

It can't be the router, renewing DHCP lease or switching off the Use Passive FTP Mode (PASV) fixes described on here but something the Mac does.

Does anybody know? It's a massive inconvenience and I hate not knowing.

Thanks

Will

Mac Pro, iOS 10.1, null

Posted on May 2, 2017 1:43 AM

Reply

Answer 1

May 2, 2017 5:50 AM in response to MrMonoboy

Your Mac uses a random self-assigned IP address to identify itself when it starts up the Ethernet port (or any other networking port). It then sends a request for someone on this subnet to please provide a "good", Routable IP address, to replace the temporary self-assigned address.

When it is stuck with the self-assigned address, this means it was not successful in reaching the Router and getting a good IP address back from the Router.

It is really easy to overthink this massively. These problems tend to be caused by simple physical issue such as flaky cables (mis-wired, broken wire), or bad ports on computers or Routers. To debug, substitute know good part until the issue subsides, and see if the issue follows cables, ports on computer, ports on Router, etc.

Reply

Answer 2

MrMonoboy Author

Level 1

20 points

May 2, 2017 5:56 AM in response to Grant Bennet-Alder

Something is interrupting ET from phoning home on startup. It's that simple. Fair enough.

Thanks for the insight Grant, much appreciated.

Reply