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DNS Doctoring

Posted on 2006-05-17
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Hello everyone,
This question may have been asked here before albeit in a different scenario. Here is the problem that I am facing.

We have our internal AD DNS server sitting behind a Cisco PIX 506 firewall. We are in the process of changing our ISP's. We have, in the firewall config, the use of the alias command. This command is not supported in the PDM and I keep getting a message when I start the PDM. This means that the only way in which I can configure the pIX is through the command line.

Now with the move to the new ISP - I would like to do away with the alias command. In reading a few articles on this site regarding DNS doctoring, there have been a couple of suggestions. However the scenario's presented are slightly different from ours. We host quite a few websites on the servers inside our network. So also mail (OWA). I would like to be able to browse the websites from within the network without any problems (the internal DNS server has the records for the web sites). So if my internal DNS server has all the internal IP addresses for the web servers - I should not need any alias command on the firewall. Am I correct in that assumption? For external clients accessing my internal web servers we have the access list as well as the static entries in the firewall configuration.

In case the static command is used with an outside NAT "static (outside,inside) 10.10.4.9 209.x.x.x netmask........" will that be helpful?

One important factor is that our internal and external DNS names are the same. I am maintaining 2 DNS servers.

Any help in this matter will be highly appreciated.

Regards
RRC
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Question by:ravichetal
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stressedout2004 earned 500 total points
ID: 16703406
DNS doctoring is applicable only if the DNS is on a lower security level. PIX cannot do anything if the traffic does not pass through it in the first place. So if your saying that your internal DNS resolves the internal IP address of the web server and clients on your LAN points to this DNS server, then you have nothing to worry about.

>>One important factor is that our internal and external DNS names are the same

It doesn't matter, as long as your internal network points to the internal DNS server which resolves to the internal IP address of the server. The external DNS on the other hand should handle request coming from the outside and resolves to the public IP address of the server. You should be all set.

In this setup, you should also be able to get rid of the alias command.
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