computer networkers, please rise

[Eric]

Hi,

I'm gettin' jiggy with my home network, and I am getting myself wrapped
around the axle.  Can you help?  I'll make this as short as possible,
consistent with giving all necessary info:

I have the following setup at home:


LAN							 WAN

[HOST_C
(192.168.0.3/24)]--------------[HUB]------------[HOST_A_(192.168.0.1/24)(wit
h_DSL_CONNECTION)]-------------QWORST




Between HOST_C and the HUB, I want to insert HOST_B.  At some point
hopefully, HOST_B will be a firewall; hence I need to get it to forward some
packets which is what I am testing now.  HOST_B's name is "Lappy" and it is
a RedHat 7.1 Laptop with two PCMCIA slots, into which I have put two 3C59x
cards.  I know how to configure an eth device.  To get this setup here to
work, it seems as though I should just do it twice  and then enable packet
forwarding; is this correct?  That is what I tried initially, but it was all
down hill from there.

When I insert HOST_B between HOST_C and HUB, several different problems
arise.  Basically, instead of telling all the configurations/scenarios I
tried, it boils down to the fact that if I keep all hosts on 192.168.0.0,
either HOST_C can ping HOST_B and vice versa, but HOST_B cannot access the
Internet, *or* HOST_B can access the Internet, but HOST_C and HOST_B cannot
ping each other.  A few times, I managed to get it so neither alternative
worked.  Sometimes, in order to get functionality on eth0, I would have to
unplug eth1, etc.  It seems like HOST_B gets confused when dealing with two
NIC's with a hosts on each side, and can only figure it out when one "side"
is removed from the picture.

Alternatively, I tried making both HOST_C and eth0 on HOST_B be on their own
network (10.0.0.0), while keeping eth1 of HOST_B and HOST_A on 192.168.0.0,
but it just got worse.  I can provide details if necessary, but there are so
many different combinations that my head is spinning.

Let me say that I have enabled forwarding, and between HOST_C and HOST_B, I
was using a crossover cable, but between HOST_B and HUB, I was using a patch
cable.  I have tested both of my PCMCIA slots, both my 3com cards, and
cables--all seems to work.  I have rebooted at least 35 times today messing
with this and that, and I feel nauseous.  I haven't felt this bad since the
last episode of Emeril.

Could anyone start by telling me whether I should have two networks 10.0.0.0
& 192.168.0.0, or keep everything on 192.168.0.0?  Next, do I put two
entries in /etc/hosts, one for Lappy 10.0.0.1 and another for Lappy
192.168.0.1?  I don't know what else; can anyone help?

Eric