RE: Securing DNS Server

["Naman Latif" <naman.latif () inamed com>]

You are right for most of your assumptions. We do have an internal DNS
server, which is Primary for all the users. No user has access to the
DMZ DNS Server. Also the Internal DNS server is NOT accessible from
outside.
However the internal DNS server has the DMZ DNS server as its forwarder.
So if an internal user query cannot be resolved by the internal DNS
server, it is forwarded to the DMZ DNS Server.This is where my questions
is, 
1. If the DMZ DNS server needs to contact some external (root)server for
resolving the query, then how do I control that ?

Regards \\ Naman


> -----Original Message-----
> From: Michael Vaughan [mailto:list () predator-hunter com] 
> Sent: Monday, November 04, 2002 12:50 PM
> To: Naman Latif; 'security-basics'
> Subject: RE: Securing DNS Server
>
>
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> Folks,
>
> If I am not mistaken, the DNS server in the DMZ should be a SECONDARY
> IE: a non-writable database.  Furthermore, the DNS server on 
> your internal network should be the primary giving ONLY 
> appropriate information regarding the location of external 
> services. IE: not allowing DNS zone transfers except from 
> specific servers...etc. 
> Essentially, the external DMZ server services external 
> requests for resolving services offered in the DMZ ONLY and 
> the internal DNS server (Primary) offers services to internal 
> clients for resolving outside sites & services.  My question 
> is why would you be allowing ANY outgoing connections from 
> your DMZ DNS server to external root servers other than what 
> is on your site? If you have other services located at other 
> locations...you can add those to the DNS manually or through 
> zone transfer. I would propose that the DMZ DNS server should 
> ONLY resolve your DMZ services and no one else's. IE: Why 
> would I want someone using my DNS server externally to 
> resolve yahoo? Basically I am saying that if the service can 
> not be resolved externally to your site(s) then it should 
> fail. Your internal DNS server would service all of your 
> internal clients and would not be accessible from external 
> sources period.  There are notable exceptions depending on 
> your requirements but am I missing the point of your 
> question?  I am assuming you have a DMZ and you are in NO WAY 
> allowing anyone to connect to your internal network directly. 
>  Is that correct?
>
>
> - -Michael Vaughan
> mvaughan () predator-hunter com
> http://www.predator-hunter.com
>
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> - -----Original Message-----
> From: Naman Latif [mailto:naman.latif () inamed com] 
> Sent: Friday, November 01, 2002 7:31 PM
> To: security-basics
> Subject: Securing DNS Server
>
> Hi,
> I am trying to restrict Access to our DNS Server from Outside 
> using a Cisco IOS Firewall. Initially we only had Port 53 
> Access to this Server from outside. But it turned out that 
> when our DNS Server has to query a root name server, it sends 
> out a UDP query with a random higher (>1023) source port 
> number, which means that I will have to open >1023 Ports 
> access to this server from outside. In this situtation How do 
> I protect my DNS server from outside attacks on higher port 
> numbers ? Is there a range of Source Port numbers that a BIND 
> DNS server would use, when querying outside servers ?
>
>
>
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