La commande mii-tool indique dans quel état se trouve la carte réseau :

eth0: negotiated 100baseTx-FD flow-control, link ok

On voit donc ici que la carte réseau est à 100Mb/s en Full Duplex et que le lien est UP.

Avec mii-tool -v, on a encore plus d'informations :

eth0: negotiated 100baseTx-FD flow-control, link ok   
  product info: vendor 00:10:18, model 23 rev 6   
  basic mode:   autonegotiation enabled   
  basic status: autonegotiation complete, link ok   
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
  link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control

On peut aussi utiliser la commande ethtool eth0

Settings for eth0:
        Supported ports: [ MII ]
        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: 100Mb/s
        Duplex: Full
        Port: MII
        PHYAD: 1
        Transceiver: external
        Auto-negotiation: on
        Supports Wake-on: g
        Wake-on: d
        Link detected: yes