> Give the 2nd ether on the firewall, say, 10.0.0.128/29 (for instance).
> You assign your machines 10.0.0.129, 10.0.0.130, etc.  Then you setup the
> port forwarding on the DSL router:
>
> your.machine:25 -> 10.0.0.129:25.  The DSL router sees 10.0.0.0/24 as the
> entire subnet, and it forwards the packets to the ethernet port (doing the
> NAT form your external IP to 10.0.0.129).  The firewall sees a packet
> coming in for 10.0.0.129:25, doesn't do any NAT but just filters, and
> sends it on it's way.
>
> So your DSL router thinks it's on a /24 network, the firewall thinks that
> eth0 is a /30 (just it and the router), and it's other ether port is on
> a different subnet (you have to make sure that what you assign your
> machines out of doesn't overlap with what the firewall sees, so it doesn't
> get conflicting netmasks.


Um, I really think you're making things more complicated than they need to be.
(I'm allergic to weird netmasks -- I suppose if you're comfortable with that
stuff, maybe you think differently).

Just use a reserved class C address internally -- 192.168.xxx.yyy and a netmask
of 255.255.255.0  (Clue for the Clueless -- "xxx" must be *identical* on every
internal box, "yyy" must be *unique*).

The end result is more or less the same, I just find it easier to deal with
mentally when different networks actually *look* different.


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