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detect dns server

Posted on 2013-01-06
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sounds like a strange question, but is there a way to detect all dns servers on our internal network?
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Question by:al4629740
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gt2847c earned 400 total points
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Several possible ways to discover active servers, not necessarily all of them (especially if someone is attempting to conceal them)...

Cisco and other enterprise class network equipment support netflow collection.  Using netflow data you can look for traffic on TCP and UDP port 53.  Any internal network address answering traffic on 53 will likely be a DNS server or doing something it isn't supposed to which is still interesting.

Placing a sniffer (Wireshark, TCPDump, etc) in a central network traffic location and mirroring traffic to it can also be used to scan for the same traffic as above.

Actively scanning for systems answering on TCP and/or UDP 53.  NMAP is a free port scan utility that can do this.  There are plenty of commercial offerings as well.  Anything listening (and answering) on 53 is either a DNS server or again doing something it probably shouldn't be...
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