We have issues with only these MacPro models negotiating 100/full on our 3560 switches running IOS version 12.2(25r). If I set the port to auto/auto on both ends it negotiates 100/half. If I hard code the port to 100/full and then have them them hard code the box to 100/full it says cable unplugged, and same result if the switchport is at auto/auto.
This wasn't a problem with the previous model of MacPro. At least we could get them to hold at 100/full by setting the speed/duplex to auto/auto in the past. And for just a little more detail if it is a 3560g switch then we can set the port to auto/auto on the switch and the machine hard coded to 100/full works.
The only difference I can find between the MacPro tower model (early 2008) model that works, and the (early 2010) is the chipset is different. The (early 2010) model uses the Intel 82574L chipset, as the (early 2008) uses Intel 8254X.
Has anyone else ran into this issue? Again we can apply a workaroun on the 3560G, but the regular 3560 doesn't have gigabit speed so it isn't a possibility.
not sure if this will work but I found the following thread:
sudo ifconfig en0 media 100baseTX mediaopt hw-loopback
unfortunately this is not persistent across reloads