Re: abnormal overruns?

From: Bill Fink
Date: Sat May 24 2008 - 21:10:54 EST


On Fri, 23 May 2008, marky wrote:

> Upon checking the output from ifconfig, I've noticed one of my ethernet
> cards has an unusually high overrun count:
>
> eth0
> RX packets:893306935 errors:5 dropped:0 overruns:29316 frame:5
>
> Coincidentally, eth2 on the same box has
> RX packets:832545758 errors:0 dropped:0 overruns:5116 frame:0
> TX packets:873232422 errors:0 dropped:0 overruns:152 carrier:0
>
> eth0 is our lan interface and eth2 is our interface that corresponds
> with the cable modem. I believe eth0 is a 3com NIC and eth2 is an
> eepro100 card.
>
> The box itself acts as a router for about 6 other machines in our lan
> running kernel 2.6.
>
> Testing this when transferring a 30 MB file to the router itself yielded
> an increase in overruns. This seems abnormal as 29k overruns seems quite
> high. The computer itself is somewhat overkill for router purposes so it
> makes me wonder, is this an error in the driver or is there a bottleneck
> somewhere else?

Do you have flow control enabled on eth0 and eth2? You can check
with "ethtool -a ethX".

Also check the settings of /proc/sys/net/core/netdev_max_backlog
(for the receive side) and the txqueuelen from ifconfig (for the
transmit side).

And "ethtool -S ethX" will give more detailed device statistics if
the driver supports it. You can then check the driver specific
documentation (if available) to get more detailed info on any
relevant driver error counters.

-Bill
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