[OliverTwist]

My ethernet connection hasn't worked for four days now. Network Preferences says it has a self-assigned ip, presumably because it can't negotiate an IP with the router.

Anyone experience this before, and have a possible solution? Thanks.

[Tomchu]

It could be anything from your router's DHCP service having crashed, to a cable that went bad (perhaps a chair rolled over it, etc.), to your network interface or OS not functioning correctly.

Easiest things to try first are to reboot the router, reboot your computer, and to try a different cable. :-P Once you rule those out, then you can start looking into more specific causes.

[fesdds]

I have one computer in my office that this happens to about once every 6-9 months. It is because of a problem with my ethernet cable. I haven't replaced the cable because it runs the length of the building and it happens so infrequently. When the cable near the network switch gets bumped the iMac loses its connection to the router and it self-assigns an IP address. It used to drive me crazy, but now I know to go unplug and replug the cable into the switch then reboot the computer. I don't need to reboot the router. For my situation, the computer must be rebooted, no matter how much I reset the settings in System Preferences under Network it will not correct until the reboot.

[Cold Warrior]

It may not be the cable as much as the way the ethernet head was crimped. Most organizations and IT people crimp their own CAT5, and often enough there are flimsy crimps. Have a tech person cut the end and redo the crimp so the strands sit better in the head and the head better in the switch.

[OreoCookie]

If you're running Leopard, try disabling the Firewall and `Renew DHCP lease'. This has worked on my dad's old PPC Mac mini. For some reason, the necessary DHCP traffic was blocked.

[OliverTwist]

It can't be an ethernet or router issue, because I connected a windows laptop to the same cable and it worked fine. My iBook is the only one that does this. I do not have the firewall running at all, so that can't be it either.

Thanks for the suggestions though. Still no internet :-(

[ghporter]

When you tried the same cable with another computer, did you try it with the same port on your router? Have you tried a different cable with your iBook? It's sounding like this is an issue with the iBook's Ethernet port, which is not good news.

[OliverTwist]

I just tested another mac and it's having the same issue. In other words, all the PCs connecting via ethernet work fine, but all the Macs do not.

Oh, and I booted an Ubuntu livecd on my Mac, and it couldn't connect either, so it isn't a software issue. I'm starting to conclude that something is wrong with the physical build quality of my Macs.

[ghporter]

I think you'll find that the hardware quality of Macs is a bit superior to that of PCs. I doubt it's something to do with the hardware on ALL of your Macs. It's likely more to do with the router's implementation of DHCP, or something similar. It CAN be a router issue, since some companies don't necessarily "perfectly" implement DHCP servers, NAT and so on, and Macs are very thoroughly standard-compliant when it comes to network connections. Further, which is more likely-that ONE device, your router, has a problem, or a BUNCH of devices ALL have the SAME problem? Occam's Razor says it's the router.

If you have an Intel Mac, try using Windows (installed through Boot Camp, with the Mac drivers installed) and see if you can connect. Betcha you can, and that will prove that your Macs' hardware is not at fault.

[Cold Warrior]

Is it possible your workplace upgraded the security and now employs MAC address filtering?

[OliverTwist]

Problem solved! I actually can't explain what the problem was, but my Macs both connect to the router just fine now. I replaced ethernet cables, re-arranged ports on my router, changed settings, and so on. Very strange.

Thanks very much for your help, guys.

[Cold Warrior]

What settings did you change?