Re: Firewall on server itself

[Brad Arlt <arlt () cpsc ucalgary ca>]

On Wed, Jun 25, 2003 at 02:24:46AM -0400, Anish Basu wrote:
> web server will be running Red Hat 9.0.  Is there any reason to install
> and configure firewall software such as IPTables on the web server itself?
> Are there any advantaqes or disadvantages to having two firewalls set up
> this way?

There are three, as I see it, reasons to setup a firewall on a server
and at the boundry.

 - You protect your server from the other servers
 - If your boundry firewall malfunctions, your server's firewall is
        much better than nothing
 - You can be super restrictive on the server firewall, maybe more so
        than makes sense on the boundry firewall

The downside:

 - You now have one more firewall to maintain
 - You will feel super secure behind two firewalls, for no reason,
        and let other things slide because of it - like patching the
        web server software which isn't protected by the firewall by
        definition
 - Bugs in the server's firewall software will reduce the stability of
        the server (happened to me just last week - IPTables got very
        unhappy about something and we had to reboot)
 - There is a performance price to pay for server firewalling

If the following is true, the server firewall buys you little:
 - your server is in your DMZ
 - your server has no sensitive data
 - your server has no unique data
 - none of the machines in your private network trust any machine in
        the DMZ
 - you can restore your server to 100% functionality in 4 hours or less
        well... maybe 95% functionality, my servers rarely are 100%
        functional ;)

If any of those are not true, making them true will aid you better
than a server firewall.  If you can't make all of them true, try
harder.  If you still can't then I'd say add the server firewalling.
-----------------------------------------------------------------------
   __o          Bradley Arlt                    Security Team Lead
 _ \<_          arlt () cpsc ucalgary ca                University Of Calgary
(_)/(_)         T minus 4 weeks to Peru         Computer Science

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