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Date:      Tue, 10 Dec 2002 20:56:25 -0700
From:      Lorin Lund <wbs@infowest.com>
To:        FreeBSD Questions <freebsd-questions@freebsd.org>
Subject:   single nic firewall - what are my vulnerabilities.
Message-ID:  <UOYW4X2ZYVYVAYWSOVSQKXR9585JHGA.3df6b769@Presarionb>

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I just got DSL.  My FreeBSD box that used to be my dial-up gateway
is now my DSL gateway.  I don't have any spare NICs right now so
I have my home network defined as subnet 169.254.0.xxx.  The DSL 
'modem' defines itself as 192.168.0.1.  So the NIC in my FreeBSD 
gateway is defined as 192.168.0.4 and aliased to 169.254.0.1.

natd is running with -a 192.168.0.1 .
In rc.conf 
firewall_type="OPEN"
So right now I don't have any firewall protection.  ipfw is just
there to host natd.  Assuming that I can create the right set of
ipfw rules (and I suppose that could be complicated by the aliasing)
are there any other vulnerabilities?  Is there any way that anything
dangerous can go directly from the DSL 'modem' to one of the other
PC's that is on the internal subnet?  I would think that being on 
separate logical subnets would keep any TCP/IP traffic or UDP/IP
traffic from getting around the firewall but are there any other
packet types or protocols that could slip through and cause trouble?



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