RE: Need TCP-IP guru advice - 2 networks, 1 firewall

On Fri, 23 May 2003, Jim Essinger wrote:

> Topology looks something like this:
>
> -----------------
> |                    |
> |  AS/400      |   TR Card 1 (172.24.1.1) --> PC's -->  Firewall
> (172.24.1.10) --> More PCs
> |                    |
> |                    |   TR card 2 (172.22.1.1)  -------> PC's 
> (172.22.***.***)
> ------------------
>
> Is there something on the PC that needs to know about the other
> network?  Something in the hosts file?  Or entries in the DNS on the AS/400
> to point to the firewall??  I know that TR Cards need to know about each
> other and have a path to forward traffic.

In order for the response to the ping to get back to the host that
originated it, something needs to know about the other network.  You have
2 networks:  call them A and B.  The hosts in network A all point to the
firewall/router as their default route.  The hosts in network B all point
to the AS/400, which forwards traffic on to network A eventually reaching
your firewall/router (if the packets are destined for networks outside of
A and B).  So let's say you ping from a host on network B to a host on
network A.  The packet goes to the AS/400 and is then forwarded to network
A.  The destination host on network picks up the packet and attempts to
respond.  Where does it send its response to?  Well its default route
(i.e. where all packets go not destined for network A) is the
firewall/router, so it send its response there.  Does the firewall/router
know to send packets destined for network B to the AS/400?  I'm guessing
that it doesn't.  Simply add a route to the router for network B pointing
to the AS/400.

James Rich