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Microsoft Windows Performance Monitor, DNS, and "Unmatched Responses Received"

Posted on 2013-06-27
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Last Modified: 2013-06-28
We've just replaced our aging, self-hosted, BIND DNS, public-facing physical name servers with Windows Server 2012 DNS virtual servers.  They're operating quite well.

Using Windows Performance Monitor, we're tracking the "UDP Queries Received/sec" and "UDP Response Sent/sec" which look good, peaking in the 300-400/sec range.

We also took a look a the "Unmatched Responses Received" statistic, currently at 427 after 10 days of uptime.  In comparison, this number is negligible compared to the successful response rate, but the interesting thing is that I've been unable to find any information to determine what an "Unmatched Response" is when related to DNS.

My searches to try to explain or define it have only found one or two mentions in passing, in discussions of DNS DDOS attacks, and in logging.  Can anyone fully define this for us, and explain what a sudden increase in "Unmatched Responses" might indicate?  Any URLs to plain, detailed information are certainly appreciated.

Thank you.

Dimarc67
Frederick, MD
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Question by:Dimarc67
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DrDave242 earned 500 total points
ID: 39286000
An unmatched response appears to be a DNS response packet sent to a machine that never issued a corresponding DNS query. This typically indicates that there's some source address spoofing going on somewhere, and a large number of these can indicate that a DNS amplification attack (a type of DDOS attack, as you said) is underway. This TechNet article does a good job of explaining how it all works.

I wouldn't worry about 427 unmatched responses over ten days, but if that counter suddenly spikes, you may be under attack.
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by:Dimarc67
ID: 39286042
Great response, Doc.  Thorough, corroborated, and specifically addresses the question.  Thanks much!
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