ethtool - Display or change ethernet card settings
Full duplex -sending and receiving data simultaneously.
half duplex - half duplex, you can either send or receive data at a time (
to find nic card half or full duplex
[root@machine1 ~]# dmesg | grep -i duplex
e1000e: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: Rx/Tx
[root@machine1 ~]# ethtool eth0
Settings for eth0:
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 pause frame use: No
Advertised auto-negotiation: Yes
Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 2
Transceiver: internal
Auto-negotiation: on
MDI-X: off
Supports Wake-on: pumbg
Wake-on: g
Current message level: 0x00000007 (7)
Link detected: yes
[root@machine1 ~]# mii-tool eth0
eth0: negotiated 100baseTx-FD flow-control, link ok
You can change the ethernet setttings using ethtool -s option
ethtool -s eth0 speed 100 duplex full
ethtool -s eth0 speed 10 duplex half
OR
mii-tool -F 100baseTx-HD
mii-tool -F 10baseT-HD
