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Date:      Sun, 27 Jun 2004 15:54:32 -0400
From:      Chuck Swiger <cswiger@mac.com>
To:        Romain Kang <romain@kzsu.stanford.edu>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: IP alias + NAT through a single NIC?
Message-ID:  <40DF25F8.1050305@mac.com>
In-Reply-To: <200406261600.i5QG07kG008437@kzsu.stanford.edu>
References:  <200406261600.i5QG07kG008437@kzsu.stanford.edu>

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Romain Kang wrote:
> I have a single physical network with 2 disjoint address spaces in
> it.  Logical Net 1 is routable, while Logical Net 2 is in private
> space intended to keep devices there safe from the outside.  Now I
> need to allow some Net 2 devices the capability to access the web,
> and putting in a second physical net is impractical.
> 
> Can a FreeBSD box with just one NIC on the physical net be used as
> the router between the logical nets?

Yes, although using one NIC compromises security a great deal compared with 
having two physical subnets seperated by a packet-filtering firewall.

Set up an interface alias via ifconfig to go on the second network, enable 
ipforwarding and presumably NAT.

> If so, could it be used to limit outside access from Net 2 by hardware address?

All outside traffic is going to go through the machine used as a router and 
acquire it's hardware address.  If you have another router on net 1, blocking 
packets from that MAC on all of the hosts on net 2 would be useful, but you'd 
have to do it for each client machine, not just on this FreeBSD box itself.

> Or is there a proxy that would work for this configuration?

Running a proxy server on the FreeBSD box is more secure than providing 
routing and NAT for the machines on net 2.  squid works fine for this.

-- 
-Chuck



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