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Steps to enable auto-negotiation for your NIC

Tags: Auto-negotiationDuplexNIC

Published on: August 9, 2014 by Sreejith K R

Steps to enable auto-negotiation for your NIC


Currently, your network card should be set to 100 Mbit Full Duplex, and auto-configuration (auto-negotiation) should be off, Let us see how to enable auto negotiation


<pre># ethtool eth0 | egrep "Speed|Duplex|Auto-neg"

Speed: 100Mb/s

Duplex: Full

Auto-negotiation: off

After the adjustment, auto-negotiation must be activated to ensure the full network speed. Doing so will interrupt the network connection for a few seconds.

# ethtool -s eth0 autoneg on

After this change check to make sure the speed is now correct:

# ethtool eth0 | egrep "Speed|Duplex|Auto-neg"

Speed: 1000Mb/s

Duplex: Full

Auto-negotiation: on

If instead the output shows:

Speed: 100Mb/s
Duplex: Half
Auto-negotiation: on

then the switch your server is connected to has not yet been changed. In this case, you can once again set the speed manually:

# ethtool -s eth0 speed 100 duplex full autoneg off

If the speed has been set correctly, then the static setting must be removed from the configuration files.

The following line in the file /etc/network/interfaces needs to be removed or changed to a comment (with a comment character #):

post-up mii-tool -F 100baseTx-FD eth0


The following line in the file /etc/sysconfig/network-scripts/ifcfg-eth0 needs to be removed or changed to a comment (with a comment character #):

 ETHTOOL_OPTS="speed 100 duplex full autoneg off" 

The following line in the file /etc/sysconfig/network/ifcfg-eth0 needs to be removed or changed to a comment (with a comment character #):

ETHTOOL_OPTIONS="speed 100 duplex full autoneg off"

Windows Server 2008
First, open the Change adapter settings page in the Network and Sharing Center of the Control Panel.


Via the properties of the LAN connection you can configure the network interface card.


Under the “Advanced” tab you will find the option “Speed & Duplex“.


Select “Auto Negotiation” once the reconfiguration of the switch has been done.


When you confirm the setting with “OK” the network connection will be briefly interrupted. You may then need to reconnect via Remote Desktop.

VMware ESXi

Changing vmnic1 to auto-negotiation:

# esxcfg-nics -a vmnic1

Enter esxcfg-nics without any parameters to get help. For more information on configuring the duplex modes and auto-negotiation, see kb.vmware.com/kb/1004089



Category : Linux

Sreejith K R

Sreejith K R

Sreejith is an early adopter of upcoming technologies and has got immense interest on exploring its features for improving productivity. He is quite proficient in various scripting languages and loves to enhance work flow through development of various automation scripts. He is video game junkie and is a perfect choice for the position of a game tester :-)

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