Feb 022014

This is something I missed myself and discovered recently.  Happens to anyone. What you experience is that despite having Gbps port and the provider confirming it you are not able to see that speed in Up/Down.

You will also observe packet loss at the last/first mile on your service side. The fix is simple.


 #ethtool eth0 | egrep "Speed|Duplex|Auto-neg"
       Speed: 100Mb/s
       Duplex: Full
       Auto-negotiation: off

This shows the problem. If you have multiple interfaces test them all.

The fix is as such.

#ethtool -s eth0 autoneg on

Then test again with above command. Output should be like so.

# ethtool eth0 | egrep "Speed|Duplex|Auto-neg"
       Speed: 1000Mb/s
       Duplex: Full
       Auto-negotiation: on

If you see otherwise it means you don’t have the connectivity from your provider on the switch or your network isn’t 1Gb/s. Revert your changes
#ethtool -s eth0 speed 100 duplex full autoneg off

To make the change permanent check your respective OS interface configuration and remove the lines.

Ubuntu/debian like
in /etc/network/interfaces comment out
#post-up mii-tool -F 100baseTx-FD eth0

in /etc/sysconfig/network-scripts/ifcfg-eth0
comment out
ETHTOOL_OPTS=”speed 100 duplex full autoneg off”

  2 Responses to “[Fix] My servers have 1Gbps network but it’s slow”

  1. Did you see a speed improvement then, I take it?

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