Ethernet Auto-Negotiate fails in 3 Macs

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zaxcom

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Over the past year I have had 2 older iMacs and 1 600MHz iBook brought to me with what appeared to be dead Ethernet ports. For all outward appearances the ports were DOA. No router or switch would show any sign of life on the Ethernet ports when hooked up to these Macs.

BUT in each case I found that if I went into the Ethernet settings and turned off the Auto-Negotiate and manually entered the speed and duplex the ports would come to life. In most cases at any speed/duplex I choose, although one iMac would only connect at 100/half.

So how could a port that had worked flawlessly in AUTO for several years just suddenly decide one day not to negotiate, but still work just fine when forced into a mode?

Has anyone seen this or found a cause or solution?

Thanks.
 
Sometimes doing an open-firmware NVRAM reset helps with seemingly "dead" ports... boot into open-firmware (hold command-option-O-F while booting), and at the prompt type "reset-nvram" (no quotes, then hit enter), then type "reset-all" (no quotes, hit enter).

Have you made any modifications to the switches/hubs/routers that the machines are connected to? Are you using quality cabling? What kinds of switches/hubs/routers are these Macs connected to -- it sounds like the switch isn't allowing the computers to fully determine what kind of link they're connected to... why it would work for years on AUTO but cease to work suddenly is beyond me, as well...
 
'So how could a port that had worked flawlessly in AUTO for several years just suddenly decide one day not to negotiate, but still work just fine when forced into a mode?'; for one reason - newly installed software. Be it Apple specific or third party.

All too often when solving some ones problem(s), do they then say - 'oh yes, I did install ...'.
 
In each case they claim no software was added. The latest one says it worked fine on a Tuesday night, but when she turned it on Wednesday morning it was dead.

They not only stopped negotiating on their own routers and modems at their homes, but also on my routers and modems at my home. All different brands and models of equipment. I tried 2 sets of routers and cable modems and several cables that I knew were good. This all points to something in the Macs themeselves that has gone south. No cable was more than a meter long and all switches and routers and modems work just fine with other machines on the networks they were installed in.
 
A thunderstorm/power surge, perhaps? This has been known to kill modem and ethernet ports pretty good.

Did you try the open-firmware NVRAM reset?
 
I did try the NVRAM on 2 of the machines today, but it did not help. Very strange problem, especially to have 3 machines in my circle of friends all do the same thing over a period of a year.
 
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