ethtool is a more powerful cousin to
mii-tool. The following is a simple use of
# ethtool eth0
You get an output as shown below.
Settings for eth0: Supported ports: [ TP MII ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full Advertised auto-negotiation: Yes Speed: 100Mb/s Duplex: Full Port: MII PHYAD: 32 Transceiver: internal Auto-negotiation: on Supports Wake-on: pumbg Wake-on: p Current message level: 0x00000007 (7) Link detected: yes
In the output above, full duplex, half duplex and auto-negotiation have the following meanings.
Full Duplex – Logic that enables concurrent sending and receiving. This is usually desirable and enabled when your computer is connected to a switch.
Half Duplex – This logic requires a card to only send or receive at a single point of time. When your machine is connected to a Hub, it auto-negotiates itself and uses half duplex to avoid collisions.
Auto-negotiation – This is the process of deciding whether to work in full duplex mode or half duplex mode. An Ethernet card supporting auto-negotiation will decide for itself which mode is the optimal one depending on the network it is attached to.