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<p class="MsoNormal"><span lang="EN-US">We have a problem with one of our firewalls caused by DNS peaks. Once or twice a day a DNS burst (20K requests/15sec) kills all connections on the firewall.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The firewall is due for replacement but in the mean time we would like to stop these peaks at their origin or at least try to limit their impact.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">We have 6 dns servers (bind) on our campus, that are all authoritative for our domains and also resolver for our campus hosts.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Most of our clients however use our AD/LDAP/DNS Microsoft servers as their resolver, which on their turn contact our 6 dns servers for further resolving.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">What we figured out by packet capturing, is that at a certain point in time these AD/LDAP/DNS servers start ‘collecting’ dns requests without sending them further and then in a burt pass them on to our 6 dns servers which
try to resolve these queries. Due to the fact that one request of a client mostly results in several queries of our dns servers to the outside world (root server contact, NS record resolving,..) , this results in a burst of dns requests through our firewalls,
killing them.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I have 2 questions, one, is there a way to rate-limit the amount of request a single client (the AD servers in this case) can have standing out against a bind server ? Kind of rate-limiting parameter for bind name server.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Two, has anyone already seen this type of behavior on a Microsoft AD/LDAP/DNS server and has a clue what could cause this stalling ? Solving that would be the best solution.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks in advance for any suggestion, answer,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:NL-BE">Wim Holemans<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:NL-BE">Netwerkdienst Universiteit Antwerpen<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:NL-BE">Network Services University of Antwerp<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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