[E] Re: strange problem with query being dropped/ignored by the BIND process
Marc Richter
marc.richter at de.verizon.com
Wed Jun 28 15:31:41 UTC 2017
Hi Ben,
thanks for the answer.
Yeah, I think you are right. I see a lot of udpInOverflows on the system,
which suggest that the receive buffer is too small indeed.
Is there any kind of recommendation or best-practice advice what the
buffers should ideally be set to on Solaris ?
I did search the ISC Knowledge Base, but didn't find any useful advice.
Regards
arc
On 06/28/17 14:37, Ben Croswell wrote:
> Have you checked deeper at the OS level? I have seen on Linux DNS servers
> silent drops of queries on very busy servers that were exhausting UDP
> receive buffers.
>
> On Jun 28, 2017 10:26 AM, "Marc Richter" <marc.richter at de.verizon.com
> <mailto:marc.richter at de.verizon.com>> wrote:
>
> Hi,
>
> we have a setup here consisting of a recursive DNS server and two
> monitoring servers. The monitoring servers sent a test query to the DNS
> server once every two minutes to check if it is answering properly.
>
> We now have the problems that these test queries are timing out from time
> to time, (correctly) resulting in alarms in our monitoring system.
>
> I have checked this now and noticed that each time we see that alarm, the
> query sent by the monitoring server is not being answered at all.
> To debug that I ran tcpdump on both the monitoring server and the recursive
> DNS server. I see the query being sent out on the monitoring server and I
> also see the query being received on the DNS server, however there is no
> response sent to this query at all.
> Looking at the query log, which I enabled temporarily, the query is also
> not logged there so it looks like BIND is ignoring that query somewhere,
> although it is properly received by the IP stack of the server.
>
> Do you have any suggestions how to debug this further, to hopefully find
> out where these queries are stuck/dropped/ignored, as I have run out of
> ideas ?
>
> The environment is:
> BIND 9.9.9-P5 (Extended Support Version) <id:1ab232a>
> running on SunOS sun4v 5.11 11.3
>
>
> Thanks !
> Marc
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--
Marc Richter
Engr III Cslt-Ntwk Eng&Ops
Sebrathweg 20
44149 Dortmund
Germany
O +49 231 972 1293
F +49 231 972 2587
E marc.richter at de.verizon.com
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