UDP packet loss

John Wobus jw354 at cornell.edu
Thu Jun 8 20:17:59 UTC 2006

On Jun 8, 2006, at 12:07 PM, Pavel Urban wrote:

> Patrick Klos wrote:
>> In article <e69ccs$cbm$1 at sf1.isc.org>, Pavel Urban  <urbanp at mlp.cz>
> wrote:
>>> Hello,
>>> I've tried to find out the cause of some strange resolving problem
> we are experiencing. From time to time, our server seems to ignore some
> requests, while others are answered promptly. It seems to me that the
> problem is UDP packet loss.
>>> Udp:
>>>     948795842 packets received
>>>     149802 packets to unknown port received.
>>>     214635022 packet receive errors
>>>     1003702082 packets sent
>>> I've tried to increase system udp receive buffer 10x and then 100x
> with no noticable effect. Do I have to change something in Bind, too? 
> Or
> am I  completely wrong?
>> I'd say your biggest problem is the 214 million packet receive errors!
>> Find the source of those errors, and you'll likely take care of your
>> problem.  Your machine is tossing 1 out of every 4 or 5 packets!
> I've tried to 'watch' these errors and they seem to be bind-related -
> after the service is restarted, these errors stop to occur for some
> time. I thought that the cause is small udp receive buffer, but I'm not
> a network specialist - do you think it is/may be caused by something 
> else?
> Thanks!
> -- 
> ***********************************************************************
> Pavel Urban (pavel.urban at imaginet.cz)
> IOL system disaster
> Internet OnLine, owned by Cesky Telecom, a.s. (www.ct.cz)
> ***********************************************************************
>     Vegetables should not operate electronic equipment.
>            Computer Stupidities, http://rinkworks.com/stupid/
> ***********************************************************************

I run bind on Solaris and must adjust a parameter
called 'udp_recv_hiwat' to avoid losing incoming UDP packets.
After adjusting that parameter, I have to restart bind
for the change to benefit.

Perhaps Linux has a similar parameter.
The following page has general suggestions about tuning UDP:
It may not point to the Linux parameter you need to adjust,
but appears to give clues about what it might look like and
how you might adjust it.

John Wobus
Cornell CIT

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