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DMZ Name Resolution Best Practice

Posted on 2009-07-01
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Last Modified: 2012-05-07
Hello, my question is more of a design/best practice question, no real issue...

What is the best way to configure DNS/name resolution for servers in the DMZ for both internal name resolution as well as external resolution.

I'll start with Internal:  If you have an application that needs access to a specific service behind the firewall, say for example a DB server.  It obviously isn't best practice to use/hard code an IP address for the DB server in the configuration of the application needing access to the DB server so you are stuck with DNS name.  Somehow we need to resolve the DNS name to an IP.  Is it better to use the hosts file or use some type of DNS server?  If DNS is the best method is it better to have a DNS server in the DMZ that houses a zone copy of internal records or is it better to pinhole the firewall and give access to an internal DNS server?

External:
Use a DNS server in the DMZ that will perform recursive lookups or use an all together external server to perform the recursive lookups?

Any help would be greatly appreciated....

Blake
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Question by:isoperations
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Ron Malmstead earned 500 total points
ID: 24756390
Well let's start with the purpose of the DMZ.

We put those servers there to segreggate them from the network.  In the event they are comprimised, they do not have full access to the network.  As far as a router/firewall is concerned, it's a seperate network entity.

That being said.... we might not want the dmz servers to be able to resolve all the internal hosts...just the ones they need to function and communicate with directly.

You could give the server access to your internal dns servers through firewall rules....but some might construe that as a  weakening the restrictive purpose of the dmz.

In most cases, people need some traffic types to be able to traverse the dmz, (often times SQL)...but the best practice is to only do it when there is no other solution.

The idea of having another dns server, zone copy, is basically the same thing...unless you manage exactly what records are in the zone.

In short...if there are only a few hosts it needs to contact directly, then I would use a host file, or don't use hostname mappings but rather IP address for everything.  It's usually the pinhole that gets exploited first....so avoid it if you can.
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