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Date:      Fri, 18 Aug 2000 20:59:52 -0500
From:      "David J. Kanter" <david.kanter@mindspring.com>
To:        FreeBSD questions <freebsd-questions@freebsd.org>
Subject:   To firewall or not to firewall...
Message-ID:  <20000818205952.A8313@localhost.localdomain>

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...that is the question.

I have a single computer, with no internal network, that will shortly have a
DSL connection that uses PPPoE and dynamic IP address assignment. I am a
little confused with two things: one, do I need a firewall, and two, how to
construct one with a dynamically assigned IP address.

I've read that a firewall isn't really needed for one machine. Some say that
ppp filters are better here.

Nonetheless, I have turned off inetd and according to nmap these are the
ports of concern:

Port       State       Service
25/tcp     open        smtp                    
53/tcp     open        domain                  
111/tcp    open        sunrpc                  
515/tcp    open        printer                 
6000/tcp   open        X11
7101/tcp   open        unknown                 

One question that arises is when to block "in" and/or "out" connections.
It's a matter of not knowing where the "in" is coming from and where the
"out" is coming from and going to.

For instance, I should let "in" connections to port 25, right, but refuse
"in" connections to port 6000? If I refuse "out" connections to port 6000
will I then block use of X on my machine?

Perhaps I'm confused with where the firewall "sits." How correct is this
schematic:

127.0.0.1 <---> firewall <---> NIC <---> Gateway <---> Internet

Any help would be appreciated.
-- 
David Kanter


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