Sunday, June 2, 2013

Dropped rx packets in ifconfig

Default settings for NICs is good for most cases however there are times when you need to do some performance tuning.
When you start to observe increasing drops of RX packets it means that your system cannot process incoming packets fast enough. You can verify on your monitoring system to correlate this issue with increased network traffic at the same time.
# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:22:19:50:ea:76
          inet addr:192.168.x.x  Bcast:192.168.x.x
          RX packets:3208932 errors:0 dropped:19188 overruns:0 frame:0
          TX packets:1543138 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000

First verify current NIC settings:
# ethtool -g eth0
Ring parameters for eth0:
Pre-set maximums:
RX:             1020
RX Mini:        0
RX Jumbo:       4080
TX:             255
Current hardware settings:
RX:             255
RX Mini:        0
RX Jumbo:       0
TX:             255

Increasing ring buffer for rx should fix this issue:
# ethtool -G eth0 rx 512

To have this settings persistent make sure you add this command to /etc/rc.local script.


  1. Glad I could help.

    You can also have a look at rx-usecs and rx-frame parameters (ethtool -c ethX) and tune them to reduce the frame count and time latency. It will keep CPU more busy but can also save frames from being dropped.

  2. Well, I stumbled here by chance and this solved my issue. Many thanks and your site is now in my bookmarks ;)

  3. note that you can use it as ethtool_opts in /etc/sysconfig/network-scripts/ifcfg-eth0 . The variable is in capitals.