How do I change the speed, duplex on for my Ethernet card?

How do I change the speed, duplex on for my Ethernet card?

A. Under Linux use mii-tool or ethtool package which allows a Linux sys admin to modify/change and view the negotiated speed of network interface card (NIC) i.e. it is useful for forcing specific Ethernet speed and duplex settings.

Depending on which type of Ethernet card is installed on the system you need to use eithermii-tool or ethtool. I recommend installing both and use one of the tool, which will work with your card.

Task: Install mii-tool and ethtool tools

If you are using Debian Linux you can install both of these package with following command:# apt-get install ethtool net-toolsIf you are using Red Hat Enterprise Linux you can install both of these package with following command:# up2date ethtool net-toolsIf you are using Fedora Core Linux you can install both of these package with following command:# yum install ethtool net-tools

Task: Get speed and other information for eth0

Type following command as root user:
# ethtool eth0

Output:

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: d

     Current message level: 0x00000007 (7)

     Link detected: yes

This above ethtool output displays ethernet card properties such as speed, wake on, duplex and the link detection status. Following are the three types of duplexes available.

§  Full duplex : Enables sending and receiving of packets at the same time. This mode is used when the ethernet device is connected to a switch.

§  Half duplex : Enables either sending or receiving of packets at a single point of time. This mode is used when the ethernet device is connected to a hub.

§  Auto-negotiation : If enabled, the ethernet device itself decides whether to use either full duplex or half duplex based on the network the ethernet device attached to.

Or use mii-tool command as follows:# mii-tool eth0Output:

eth0: negotiated 100baseTx-FD flow-control, link ok

Task: Change the speed and duplex settings

Setup eth0 negotiated speed with mii-tool
Disable autonegotiation, and force the MII to either 100baseTx-FD, 100baseTx-HD, 10baseT-FD, or 10baseT-HD:# mii-tool -F 100baseTx-HD
# mii-tool -F 10baseT-HDSetup eth0 negotiated speed with ethtool# ethtool -s eth0 speed 100 duplex full
# ethtool -s eth0 speed 10 duplex halfTo make these settings permanent you need to create a shell script and call from /etc/rc.local(Red Hat) or if you are using Debian create a script into the directory /etc/init.d/ directory and run update-rc.d command to update the script.