If you have a Linux system, there is a tool that lets you examine and change ethernet based network interfaces.
The ethtool utility is used for querying settings of an ethernet device and changing them. The basic usage is as follows:
ethtool eth0
…and you’ll get something like this:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised auto-negotiation: Yes
Speed: Unknown! (65535)
Duplex: Unknown! (255)
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: umbg
Wake-on: g
Current message level: 0×00000007 (7)
Link detected: no
For more information take a look at man pages.