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Simple question about DNS and firewalls

Posted on 2008-06-19
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Last Modified: 2010-04-07
This is a basic question about how DNS servers communicate with the outside world when firewalled.

My understanding is that DNS servers are supposed to be placed behind a hardware firewall. They should not be firewalled themselves. This allows them to communicate freely with machines in a local subnet.  

Suppose I have a collection of IIS servers with a bunch of websites. These websites use domain names and name resolution is being provided my DNS servers.

Given the fact that the boxes running DNS services are behind a firewall, there are one of two ways I can see how this works:

possibility a) all requests involving name resolution are being routed from the IIS server to my services running DNS. The IIS boxes are publicly exposed, the DNS boxes are not.

possiiblity b) there is some limited port open or communication between the DNS box and the outside world.

I'm finding this a bit confusing because if scenario a) is true it introduces a systemic dependency on those IIS boxes, and it also makes it hard to understand how widely distributed things involving DNS -- say, DFS file replication  -- works properly if the primary actors of that are behind hardware firewalls.

Thanks...
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Question by:kennethfine
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tigermatt earned 250 total points
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I doubt either is true. If you don't have the DNS port 53 forwarded through the firewall to one of your DNS servers, then an external DNS system is resolving requests for the IP addresses of your IIS web servers. Only internal requests on the LAN will be resolved by the internal DNS servers because they are local and will be using the Active Directory DNS servers as their preferred servers.

Usually, you will have your DNS for external web domains hosted at either the web host, ISP or at a provider which you have brought in specifically to provide your DNS.

-tigermatt
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by:tigermatt
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Thanks kennethfine!
--tigermatt
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