Determine Linux ethernet interface speed and duplex

Determine the autonegotiated ethernet connection speed and duplex using the mii-tool command

Running the following command as superuser with no options will generate basic information about all of the ethernet interfaces on the computer:

mii-tool

The resulting output will look something like:

eth0: negotiated 100baseTx-FD, link ok

This output shows one interface (eth0) which was autonegotiated to 100 Mbps (100baseTx) and full duplex (FD).

Adding the -v option to the command generates verbose output and will tell you more about the interface including the manufacturer and model (if available) and the interface’s capabilities.

courtesy http://www.tech-recipes.com/rx/25/determine-linux-ethernet-interface-speed-and-duplex/