[dns-operations] max-clients-per-query limit

Shawn Zhou shawnzhou00 at yahoo.com
Wed May 17 22:40:22 UTC 2017

So if the limit is set to unlimited, bind still only recurses once for the same lookups, correct?

      From: Mark Andrews <marka at isc.org>
 To: Shawn Zhou <shawnzhou00 at yahoo.com> 
Cc: Evan Hunt <each at isc.org>; "dns-operations at lists.dns-oarc.net" <dns-operations at dns-oarc.net>
 Sent: Tuesday, April 4, 2017 11:52 AM
 Subject: Re: [dns-operations] max-clients-per-query limit

In message <317795614.485739.1491329002484 at mail.yahoo.com>, Shawn Zhou writes:
> Hi Evan,
> How long is the time window that BIND uses to calculate the identical
> lookups? Is it over 1-minute window? or 5-minute window?
> Thanks,Shawn

Whenever named recurses it looks to see if there is a existing
client already recursing for the given <QNAME,QTYPE,QCLASS>.  If
there is the client attaches itself to the lookup and waits for it
to resolve.  If there are already too many clients waiting for that
lookup to complete it drops the client which should retry a short
while later, when, hopefully the lookup has succeeded and the query
can be answered from the cache.

>      From: Evan Hunt <each at isc.org>
>  To: Shawn Zhou <shawnzhou00 at yahoo.com>
> Cc: "dns-operations at lists.dns-oarc.net" <dns-operations at dns-oarc.net>
>  Sent: Wednesday, March 22, 2017 10:07 PM
>  Subject: Re: [dns-operations] max-clients-per-query limit
> On Wed, Mar 22, 2017 at 10:05:35PM +0000, Shawn Zhou wrote:
> > What happens when max-clients-per-query is reached? say, we have 120
> > duplicate requests and the max-clients-per-query is set to 100. Do
> > the 20 "extra" requests got dropped or get timeouts or they will be
> > part of next grouped requests?
> They're dropped.
> --
> Evan Hunt -- each at isc.org
> Internet Systems Consortium, Inc.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                INTERNET: marka at isc.org

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