Thunderbolt Ethernet has a self-assigned IP address and will not be able to connect to the Internet

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Thunderbolt Ethernet has a self-assigned IP address and will not be able to connect to the Internet

I've never understood this, happens completely at random after working fine for months.

Usually, a combination of renewing the DHCP lease, trashing preferences, setting up a new location, restarting the router or switching passive FTP mode off would work. Not this time.

I've even tried using a manual IP address from the router and a different cable. I get a green light but no connection.

Utterly frustrating. Wireless works fine of course.

Anybody got any ideas? Other than forgetting about ever having a stable Ethernet connection on a mac?

OS Mojave 10.14
MacBook Pro (retina, 2014)
BT HomeHub 5
TP-Link adapter

TV connects fine. As does a MacMini. Just not the machine I use for work 12 hours a day.

I think I may actually hate computers.

MacBook Pro (Retina, 13-inch, Mid 2014), iOS 10.1

Posted on Oct 30, 2018 8:29 AM

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Answer 1

Oct 31, 2018 4:27 AM in response to MrMonoboy

What do you mean IP copied from the router?

You need to make sure that you give your mac a valid IP which is not within the range of IP's used for DHCP.

For example, if your router is 192.168.1.1 and is distributing addresses to your devices via DHCP, like 192.168.1.67, 192.168.1.68, etc you may try giving your mac an IP

like 192.168.1.100, which is unlikely to be used by another device.

You should set the subnet mask at 255.255.255.0, and your gateway as the address of your router. The DNS server could be your router, an address given to you by your ISP, or try 8.8.8.8 for one of the free google dns servers.

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Answer 2

Oct 30, 2018 11:00 AM in response to MrMonoboy

If you set it up with manual IP you have to also configure the proper subnet mask and router address. The subnet mask is *usually* 255.255.255.0 but could be different; the router address you can probably find out from the manual on your router; usually, it is 192.168.1.1 or 192.168.1.254 but could be different. Also you have to set the proper DNS server(s).

Having a green light indicates that your mac is sensing a physical connection on the Ethernet port and that it is at least communicating properly with the router.

A green light but no connection (which I take it to mean that you can't access sites on the web, for example) may just mean that the DNS server address is not set or is set incorrectly; or that the subnet mask is incorrect.

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Answer 3

Oct 30, 2018 8:46 AM in response to MrMonoboy

Maybe you need to update the firmware on your router. Or maybe you need a new router. Maybe change the Ethernet cable or the port it is connected to on the router. Does the computer work using Ethernet connected to another router?

In your network preference put the Ethernet network at the top of the list above your WiFi network.

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Answer 4

MrMonoboy Author

Level 1

20 points

Oct 30, 2018 8:56 AM in response to BobTheFisherman

I could try updating the router or getting a new one. I just can't fathom why it stops working at random.

I had issues with wireless on my iPad but that seemed to resolve itself. Lots of other devices (non-apple) connected immediately and have stayed connected.

Ethernet on my laptop has always been flaky. It's always seems to be apple stuff.

Thanks for the reply.

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Answer 5

MrMonoboy Author

Level 1

20 points

Oct 31, 2018 3:31 AM in response to MrMonoboy

I've tried every combination, nothing seems to work.

IP, subnet, DNS, all copied directly from the router control panel. I get a green light but no connection.

No doubt I'm missing something technical but it really shouldn't be this difficult to get an Ethernet connection and stay connected.

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Answer 6

MrMonoboy Author

Level 1

20 points

Oct 31, 2018 5:14 AM in response to Luis Sequeira1

Hi Luis,

I've tried a number of different IP addresses within the DHCP range (indicated on the control panel) and checked that they aren't being used by another device. I've checked that the subnet and gateway address of the router is correct. I've also put the router address in as my DNS and tried using 8.8.8.8. It still won't connect.

When I have time, I'll read up on the subject in the hope of understanding it better and try again. Until them, I give up through exasperation and will make do with a wireless connection.

Thank you for your time though, much appreciated.

Will

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Answer 7

MrMonoboy Author

Level 1

20 points

Nov 1, 2018 12:41 PM in response to MrMonoboy

This is a bit embarrassing but I'd forgotten to check the TP-Link adapter attached to the router. It had failed.

Nothing wrong with my settings, cables, router, or the TP-Link in my office.

Measure twice, cut once.

Least I know what it is now.

Thanks again for your time.

Will

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Answer 8

MrMonoboy Author

Level 1

20 points

Oct 31, 2018 3:03 AM in response to Luis Sequeira1

Thanks Luis,

I copied the IP address from my router dashboard and used that subnet mask. The green light gives me hope. I shall double check that I have the combination correct.

Will

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Answer 9

Nov 2, 2018 12:48 AM in response to MrMonoboy

Glad to see you figured it out. Thanks for sharing.

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Thunderbolt Ethernet has a self-assigned IP address and will not be able to connect to the Internet

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