Intel will not negotiate Gigabit

I just installed a new D-Link router recently that supports Gigabit speeds on the internal network.

All the other devices that support gigabit are auto-negotiating to gigabit (PC-based web server, Xbox360, PS3, TiVO).

When I look at the network information, the iMac shows that it is only negotiating to 100BaseTX, and if I force it to gigabit, it will not obtain an IP from the router.

Any ideas?

Is it a really long cable? Is it CAT5e or CAT6?

I think the answer may be the wiring you are using. This is not knowledge but guesswork. There are different wiring plans for 10 base and 100 base and I suspect the same is true for 1000 base. 100 base cables may not be wired "correctly" for 1000 base. I am assuming you are wired and not wireless.

You can do Gigabit over CAT5e cables (pretty standard these days), but if it's a long run or they're not the best quality, a good adapter will auto negotiate down to avoid reliability issues. The best rule of thumb is to use CAT6 cables, which are better shielded.

It is Cat5e and the length is not much more than the other devices... Maybe a total of 25 feet...

It is home-crimped, but the cable itself is fairly good quality.

I'll try plugging in another device to that line and see what happens.

Thanks for the input so far!

I would swap that cable with a known good one and see what happens.

Unfortunately, the cable runs through a floor, and swapping it wouldn't be very straightforward...

Agreed completely with CWA. I by the way have a Gigabit network here with an 8-Port Dlink Gigabit switch. All my systems are wired with CAT5e cables put together by me. I always get solid Gigabit connects with all systems which are both Mac and PC's. My transfer speed is 2x faster than what it used to be with 100Base-T system. Max cable length in that area of the house per port it probably only 20' though so nothing really long. Want to go up to cat-6 someday but this works great.

Sub out that cable and see if that fixes it.

loviathar said:

Unfortunately, the cable runs through a floor, and swapping it wouldn't be very straightforward...

Click to expand...

The easiest thing to do to isolate the issue would be to move your Mac closer to the router and try a known good cable with it. If it negotiates properly, then you know it's not the adapter and you know it's not the router - therefore, it leaves only one possibility - the cable.

I work as a network administrator/engineer. I've also done a few side jobs running cable in small offices and run into the exact same problem - even after recrimping both ends. I think the switches they put into SOHO/consumer-friendly routers tend to be finicky about cable quality over a long run. I've had situations where I had to actually knock the connection down to 10Mb/half duplex just to get an IP, when I was absolutely certain that the high-quality, plenum-rated cable (off the same spool that was used to wire a 120,000 sq ft office) was good and the ends were crimped right. So, don't scrimp on cabling if you're doing a permanent install. If Gigabit connectivity is important, I'd re-pull CAT6. I'd be willing to bet you'll be fine.