I'm trying to be an ISP for my mom.  I've been attempting that for my
dad too, off and on for a couple years.  It worked well enough, but
occasionally, when an incoming PPP connection comes into my main Linux
gateway box (which interconnects my LAN and cable modem) this box
hangs; I have to do a hard reset.  I've never been sure why. I've been
through a lot of kernel upgrades and a full Debian upgrade or two, so I
think it's not just some random software bug.

So now I've moved the modem to another machine.  My main gateway's LAN
interface is 10.0.0.1; the other server (which now has the modem) is 
10.0.0.2.  I'm assigning 10.0.1.3 to incoming PPP connections so as to
have a different subnet... seemed like a good idea...although I've also
tried using 10.0.0.240, doesn't make a difference.

For some reason the routing isn't working.  When a machine connects to 
this server via PPP, I can ping that machine over the PPP interface, and
it can see 10.0.0.2, but it can't see any other machines on my LAN, or the
Internet.

I tried using ifconfig promisc mode.

In /etc/ppp/options.ttyS3, I have this:

10.0.0.2:10.0.1.3
defaultroute

But one thing that's bugging me is, isn't that going to tell the PPP
client that it should use 10.0.0.2 for a default route?  I'd rather
have it use 10.0.0.1, and also tell it to use 10.0.0.2 to get to
10.0.0.1, wouldn't I?

Just for a test, I tried changing my default route on my workstation
(10.0.0.3) to 10.0.0.2.  Again, I can't ping machines on the Internet.
I think 10.0.0.2 is seeing the packets and not forwarding them on to
10.0.0.1, even though its default route should be telling it to do
that.  10.0.0.2 can ping machines on the net, but machines which try
to use it as a gateway cannot.

The client isn't a Linux box (a Mac for my mom, Windows for my dad, and
I'm doing testing with a 3com Audrey since it was handy and can do PPP)
so I need to fix this on the server side, not with unusual routes on
the client.

Crude diagram:
                  ___
                 /   | mom's Imac    ____
 ___            (____| 10.0.1.3     (____) cable modem (eth1)
|   |          ___|________    ________|___
|___|          > modem    <    >          <
_____          |          |    |  ipmasq  |
|___|          >__________<    >__________<
  |_________________|________________|
proton            nucleus         electron
(workstation)     10.0.0.2        10.0.0.1
10.0.0.3 

-- 
  _______                   Shawn T. Rutledge / KB7PWD  ecloud@bigfoot.com
 (_  | |_)                       http://ecloud.org  kb7pwd@kb7pwd.ampr.org
 __) | | \________________________________________________________________