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Trace DNS query and lookup time

Posted on 2011-03-01
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Last Modified: 2012-05-11
I am experiencing problems with 1 web site, it appears to be a DNS problem. Sometimes it takes 6-15 for the home page to open, after that it's super fast.

How can I trace DNS query, lookup time, etc, etc on Windows 7, Windows server running DNS service or linux box setup with ubuntu, or any other tool out there?

Thank you
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Question by:Coffinated
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brwwiggins earned 250 total points
ID: 35012632
You can do a simple DIG or NSLOOKUP from a client and see if it is a DNS issue. If the DNS server returns the IP address immediately you can pretty much rule it out.

Is this a .NET app? Sometimes .NET apps run slow initially because they must be compiled if they are not resident in the app pool memory. There are ways you can pre-compile apps to avoid this delay.
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by:Coffinated
ID: 35012726
It's a Joomla based website set up on fairly fast VPS. I did create a clone on much slower server and it opens instantly. not sure what the problem is, server load is low, ping very low, DNS was the last thing to check.
'dig' produced result almost instantly, I'll keep checking it when site loads slowly again.
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by:group0
group0 earned 250 total points
ID: 35031846
It sounds like a nameserver being hit somewhere in the recursive lookup is not responding, so it has to wait for a timeout before using a secondary NS to continue the lookup.  Once the final record is in your local resolver's cache, it'll continue to be quick until the TTL expires.

To bypass any caching on the part of your local resolver, use:

dig +trace www.domain.com

This will do a fresh recursive lookup each time (although other DNS servers in the chain may still cache their results).  If it pauses during the output, you'll have a good idea of which set of nameservers is the problem.  Then you can do a manual dig against each one until you find out which one is failing, eg:

dig www.domain.com @ns1.domain.com
dig www.domain.com @ns2.domain.com
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by:Coffinated
ID: 35158659
The problem was related to underlying hardware, it disappeared once VPS got moved to another host.
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