Re: dns outbound

[wyllys () reston wcom net]

On 16 May, Robert Graham wrote:
> --- Deepak Vaidya <dvaidya () clark net> wrote:
> > I have gotten a request to allow all clients behind a firewall to have
> > unrestricted access to dns servers outside the firewall.  
>
> The first answer of any firewall admin should be "only the paranoid survive".
>
> Why the heck would clients need external access to DNS servers? Barring the
> occasional network management application, there should be no reason a client
> needs direct access to a DNS server (that I can think of). This sounds like a
> program written in a clueless manner that isn't knowledgeable of proxies,
> firewalls, et al. Enabling the application might be asking for trouble, beyond
> the immediate risk.
>
> Or, is it simply that you want to run SOCKS clients and simply need the ability
> for internal machines to resolve names to addresses? You don't need direct
> access to DNS servers, you simply proxy outgoing DNS requests with your own DNS
> server.


There are plenty of reasons why internal machines need to resolve
external names.  One common reason is so that Java applets will run
on browsers inside the firewall.  Even with an HTTP proxy, many Java
applets will not work if they cannot do a reverse DNS lookup on the
host that served the applet.  

If the network is set to have a  default route thru the firewall and the
users are surfing the web without a proxy, then they will also need to
be able to resolv the external hostnames.  

Adding the ability to resolve external hostnames from the inside is not
dangerous and can be useful when properly configured.

--
W. Ingersoll
UUNET 
Reston, VA