Q: How can I determine what speed/duplex my NIC is operating at?
I have had problems with NICs autosensing the proper speed with different switches. They often-times don't put any log messages as to what they think their speed/duplex is, if you leave it to autosense.
A: Donald Becker has a utility on his Web site, mii-diag, for manipulating the MII transceivers on most fast ethernet cards directly. With it, you can check the link status, force the speed and duplex, or re-initiate auto-negotiation.
You can get it from http://www.scyld.com/diag/ .