How to see the current configuration of interface
You may do it by using either ethtool or mii-tool.
1. Using mii-tool
To see the current configuration of interface.
eth0: negotiated 100baseTx-FD, link ok
product info: vendor 00:00:20, model 32 rev 1
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
link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
You may see that the interface supports auto-negotiation (basic mode: autonegotiation enabled) and it is operating at 100 Mb/s in full duplex mode (100baseTx-FD). As you may see, the interface can operate in modes specified in the advertising line. In order to change it to 100 Mb/s, Half Duplex mode use the same command with the following options.
You may verify the new configuration by using the same command with option -v as shown above.
2. Using ethtool
To see the current configuration,
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: No
Speed: 100Mb/s
Duplex: Half
Port: MII
PHYAD: 1
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: pg
Wake-on: d
Current message level: 0×000000c5 (197)
Link detected: yes
You may change the other settings like speed, duplex and auto negotiations as follows.
[root@bash ~]# ethtool -s eth0 speed 10|100|1000
[root@bash ~]# ethtool -s eth0 autoneg on|off
You may specify all those options in a single command too.
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