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bind9 stops working when the internet connection changes

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moritzh

IS-IT--Management
May 5, 2010
1
MT
Hi!

We are using an internal server in our network as DNS to be able to handle internal domain names. It is bind9 installed on a debian system. It is a default configuration with just 5 zones added.

Everything works fine until that point when our primary internet connection fails. Our firewall then switches over to a secondary connection but normally the computers in our network do not realize that switch (they just loose internet connectivity for some seconds and afterwards are online using a new external IP address).

For some reason in such a case our internal name server is making trouble. Most of the requests he is not able to respond to anymore but when I make a nslookup I just get "SERVFAIL" back. Sometimes even for google.com etc. Some minutes later google.com maybe working but several other domains do not work. I would say for 60-70% of the nslookups I get a SERVFAIL. The local domains are always working.

When I start nslookup on the server running bind9 and choose e.g. a.root-servers.net as the nslookup server, I get proper responses for ALL requests I send.

Would be nice if anybody of you does have any hint for me which setting I could check!

Thanks,
Moritz
 
Are you using forwarders? If so, are the forwarder IP addresses for a specific ISP? If so, that could be your problem. Most ISPs do not allow queries to their internal DNS servers from addresses outside their control which is why the root-servers work.

I would contact the IPS(s) to find a remedy. The root-server method should not be a long term solution.

 
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