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RE: Securing DNS Server
From: "Michael Vaughan" <list () predator-hunter com>
Date: Mon, 4 Nov 2002 15:50:12 -0500

Hash: SHA1


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

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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

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
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
this server from outside.
In this situtation How do I protect my DNS server from outside
on higher port numbers ?
Is there a range of Source Port numbers that a BIND DNS server would
use, when querying outside servers ?

Version: PGP 7.0.4


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