logical networks (TCP routing)

[Chad R. Larson]

I would appreciate advice on how to run two separate logical networks
over a single physical network and have them interoperate.

I am currently serving as the SysAdmin for two companies.  Each of them
has an officially assigned Class B network address.  Both of them are
running IP over Ethernet (802.3) physical facilities.  The networks are
mostly 10baseT implemented with AT&T StarLan10 and David Systems
hardware.  The computers involved are 5 Pyramids (4 MIServers and 1
9845), an NCR Tower 32/600 and about a dozen AT&T 6386/33 WGS machines.
The Pyramids are running OSx5.0d and the Tower is running SysVr3.2 with
WIN/TCP as are the WGSs.

I need to be able to connect the two networks together for a short while
during a joint software development program.  I do not currently have
access to a router.  None of the machines on either network has more
than one Ethernet interface, so I cannot build a classical gateway.  I
am planning on using a MAC-level bridge on each end of a T1 to link the
networks at the physical level.  I already have the bridges (Halley
ConnectLan 100s).

What I need to know is how to build the functional equivalent of a
gateway on one of the machines to link the two IP networks.  It would
seem that by hand constructing the routing tables that this should be
possible, but I confess to being a novice in this area.

Can this be done?  Can you explain it to me?  Does the route daemon help
or hinder in this?  If I cannot construct a software solution, I will
probably try to get another Ethernet interface installed in one of the
386s and build a gateway.  Either that or open up the net mask so all
machines think they are on the same net.  The first takes additional
hardware (and the time to acquire it), the second could have
unpredictable side effects (and would have to be undone when the link is
broken).

Please e-mail to me at the below address.  I'll post the most cogent
explanation to the net.  Thanks!
	-crl
--
Chad R. Larson       ..{hrc,mcdphx,asuvax}!anasaz!chad or chad at anasaz.UUCP
Anasazi, Inc. - 7500 North Dreamy Draw Drive, Suite 120, Phoenix, Az 85020
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