Full-duplex fails on new Mac Pro

I tried it on mine and it seemed to work just fine...

Weird... have you tried both ports on your mac? or a different network drop somewhere else? (just to eliminate things as you go... )

Don't know what to say... what you want to make sure is that there are no problems with the negotiation between them..

I seem to remember long ago, that depending on the configuration of certain Cisco switches and the mac's Appletalk network number, would interfere with the negotiation of the speed. I think it had to do with the spanning-tree protocol and it would always bring you to 1/2 duplex. Its a fix at the Cisco switch... Seem to remember that by setting the same Appletalk Network number manually in the Appletalk control panel, the problem went away. That is why certain machines had the problems and others did not...

But I don't know what is your network setup like... Are you in an office env or at home?

Have you tried setting the duplex manually?

ifconfig en0 media 1000baseTX mediaopt full-duplex

There is no standard for auto speed/duplex detection, and some network interfaces don't work well with some switches. If you can't lock the speed and duplex on your switch port, then you're probably using a cheap unmanageable switch and it just may not work well with your Mac network interface.

We're very discouraged here by vendors who supply mission critical network hardware and suggest we leave the port set to autodetect. That has never been a reliable feature, even using components from the same manufacturer. We have seen 3com network adapters fail to connect properly to 3com switches, cisco to cisco, netgear to netgear, etc. If manufacturers can't make their own devices do it properly don't expect devices from different manufacturers to do it reliably.

I've had the same issues with '08 Mac Pros & '09 Mac Pros - they never automatically select 100Mbit full-duplex, it must always be done manually - and half the time selecting 100 Mbit, full-duplex doesn't work. The Macs in my office are all connected to an XSAN, so both Ethernet ports are used on different subnets - both are 100 Mbit, full-duplex. I've even seen instances where one Ethernet port works properly (allows you to manually set 100 Mbit, full-duplex) & the other port ON THE SAME MAC PRO does not... Very frustrating! Fortunately, we have HP switches (the same models for both subnets) that I manage, so when it happens, I just set the switch port to auto, the Mac port to auto & wait for the next OS X point release - & try to set them manually again. This results in half-duplex communication for a while, but at least there are no collisions.

And guess what? This morning I just updated a '09 Mac Pro from Leopard to Snow Leopard - everything worked fine before the OS update, after the reboot, I find that I can't manually select 100 Mbit full-duplex. I had hoped that Snow Leopard wouldn't have this issue...

We are having the exact same issue at our organization. This is a network card driver issue that started when the 10.5.7 update was applied to 2009 Mac Pros. After this update, 100/Full Duplex no longer works. We've opened a ticket with Apple on this; for now we found a workaround. The file that's causing the problem is IONetworkingFamily.kext located in /System/Library/Extensions/ folder. The version that came with 10.5.7 causes the NIC to stop working on 100/Full. Copy the IONetworkingFamily.kext from a 10.5.6 system. On the affected system, boot from another drive. Paste the 10.5.6 IONetworkingFamily.kext file into the affected OS's /System/Library/Extensions/ folder, replacing the original. Last step (very important), run a repair permissions on the affected OS which should set the proper permissions on the file you just copied (System account should Read & Write access). Reboot to the affected OS; NIC should now work on 100/Full. Be aware, this is only a workaround; if 10.5.8 is run on this patched OS, the issue will reoccur.

Did your ticket ever get answered? I am having the same problem and it is EXTREMELY frustrating. I'm watching all these Windows machines around me work just fine and I'm beginning to wonder if I should have made the switch to Mac at all.

Under 10.6.2 the same problem.
Apple disgrace themselves.
I hope someone finds a quick and clean solution.
Thanks nicklyaine for this workaround. I will try out and report, if its working also under 10.6.

Greetings from Germany
Avelsis

Is there any movement in resolving this issue? My network connection used to FLY with 10.5. Now it is ultra-slow and I can't set it to full-duplex 100Mbit like before. VERY frustrating. Am I an isolated case? Is there something I can ask my network administrator to do to the switches/routers? Is a fix in the works? Come on Apple, please speak up.

Solved! You have to use Terminal to enter this ifconfig command:

sudo ifconfig en0 media 100baseTX mediaopt hw-loopback

Now Full-Duplex is working! Come on Apple, this hw-loopback option should be in the Network System Preference if this is what it takes.

This DOES work, but on all of my Snow Leopard machines, it is reset back to half-duplex after a system restart.

Curious to see if everyone else has the same problem.