Ethtool - Display or change ethernet card settings

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