Change Speed and Duplex of Ethernet card in Linux

To change Speed and Duplex of an Ethernet card, we can use ethtool – a Linux utility for Displaying or Changing Ethernet card settings.

1. Install ethtool

You can install ethtool by typing one of the following commands, depending upon your Linux distribution.

Install ethtool in Fedora, CentOS, RHEL etc.:

# yum install ethtool

Install ethtool in Ubuntu, Debian etc.

# sudo apt-get install ethtool

2. Get the Speed, Duplex and other information for the interface eth0

To get speed, duplex and other information for the network interface eth0, type the following command as root.

 # ethtool eth0

Sample output:

Settings for eth0:

Supported ports: [ MII ]

Supported link modes:   10baseT/Half 10baseT/Full

100baseT/Half 100baseT/Full

1000baseT/Half 1000baseT/Full

Supports auto-negotiation: Yes

Advertised link modes: 10baseT/Half 10baseT/Full

100baseT/Half 100baseT/Full

1000baseT/Half 1000baseT/Full

Advertised auto-negotiation: Yes

Speed: 100Mb/s

Duplex: Half

Port: Twisted Pair

PHYAD: 1

Transceiver: internal

Auto-negotiation: on

Supports Wake-on: g

Wake-on: d

Current message level: 0x000000ff (255)

Link detected: yes

3. Change the Speed and Duplex settings

The next command disables Auto-Negotiation, enables Full Duplex and sets up Speed to 100 Mb/s:

 # sudo ethtool -s eth0 autoneg off speed 100 duplex full

Restart the interface to apply changes:

 # ifdown eth0 && ifup eth0

4. Change the Speed and Duplex Settings permanently

Fedora, CentOS, RHEL etc.

To make settings permanent, you need to edit /etc/sysconfig/network-scripts/ifcfg-eth0 file for eth0 interface. This file is used by RHEL, CentOS, Fedora etc.

 # vi /etc/sysconfig/network-scripts/ifcfg-eth0

Append the line as follows to disable Auto-Negotiation, enable Full Duplex and set up Speed to 100 Mb/s:

 ETHTOOL_OPTS=”speed 100 duplex full autoneg off”

Ubuntu, Debian etc.

If you need to have this settings every time you boot up the PC, you have to add a command in the /etc/network/interfaces file, so:

 sudo vim /etc/network/interfaces

And at the beginning of the file add:

 pre-up /usr/sbin/ethtool -s eht0 autoneg off 100 duplex full

That will set the parameters before bringing the interface up.

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