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Posted to users@httpd.apache.org by Steve Swift <st...@gmail.com> on 2007/08/15 10:57:37 UTC
[users@httpd] Unexpected/Unwanted DNS lookups
During a period of apalling DNS response times we became aware that our CGI
scripts were suffering an intermittent ~25 second delay between the browser
"Click" and the CGI starting execution. This seemed to be caused by DNS
lookups.
We don't use reverse DNS in our error logs, so I'm wondering what else might
be calling on DNS services?
We've now fixed the DNS issues, so this is something of an intellectual
exercise, but there is always the response time bonus of eliminating the DNS
calls to consider.
The server in question is IBM internal, so beyond the reach of all bar IBM
personnel and expert hackers.
--
Steve Swift
http://www.swiftys.org.uk
[users@httpd] Re: Re: Unexpected/Unwanted DNS lookups
Posted by Per Jessen <pe...@computer.org>.
Steve Swift wrote:
> I'm asking my system admin to setup some sort of trace right now. We
> don't have a DNS service on our own system, so tracing that will be a
> little tricky, I think.
> I may see if we can run our own caching DNS, if only for a while.
How about running tcpdump on destination port 53 on the system where
you've got apache running?
/Per Jessen, Zürich
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Re: [users@httpd] Re: Unexpected/Unwanted DNS lookups
Posted by Steve Swift <st...@gmail.com>.
I'm asking my system admin to setup some sort of trace right now. We don't
have a DNS service on our own system, so tracing that will be a little
tricky, I think.
I may see if we can run our own caching DNS, if only for a while.
On 15/08/07, Per Jessen <pe...@computer.org> wrote:
>
> If you trace what is being looked up, it might give you a clue to where
> the queries are coming from. Turn on query logging or use tcpdump.
--
Steve Swift
http://www.swiftys.org.uk
[users@httpd] Re: Unexpected/Unwanted DNS lookups
Posted by Per Jessen <pe...@computer.org>.
Steve Swift wrote:
> We don't use reverse DNS in our error logs, so I'm wondering what else
> might be calling on DNS services?
>
> We've now fixed the DNS issues, so this is something of an
> intellectual exercise, but there is always the response time bonus of
> eliminating the DNS calls to consider.
If you trace what is being looked up, it might give you a clue to where
the queries are coming from. Turn on query logging or use tcpdump.
/Per Jessen, Zürich
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Re: [users@httpd] Unexpected/Unwanted DNS lookups
Posted by Steve Swift <st...@gmail.com>.
Vincent, Thank you.
We use both "Allow" and "Deny", but only with numerical addresses or subnet
masks.
--
Steve Swift
http://www.swiftys.org.uk
Re: [users@httpd] Unexpected/Unwanted DNS lookups
Posted by Vincent Bray <no...@gmail.com>.
On 15/08/07, Steve Swift <st...@gmail.com> wrote:
> During a period of apalling DNS response times we became aware that our CGI
> scripts were suffering an intermittent ~25 second delay between the browser
> "Click" and the CGI starting execution. This seemed to be caused by DNS
> lookups.
>
> We don't use reverse DNS in our error logs, so I'm wondering what else might
> be calling on DNS services?
(Sorry if this message is repeated, the first bounced for some reason.)
Could be "Deny from some.domain" ?
--
noodl
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