Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!rutgers!njin!munnari.oz.au!bruce!trlluna!ilium!andrews
From: m.andrews@trl.oz.au (Murray Andrews)
Newsgroups: comp.protocols.tcp-ip,aus.comms
Subject: Can subnets be separated by another net?
Keywords: subnet routing
Message-ID: <1867@trlluna.trl.oz>
Date: 6 Jul 90 06:32:42 GMT
Sender: root@trlluna.trl.oz
Reply-To: m.andrews@trl.oz.au (Murray Andrews)
Organization: Telecom Research Labs, Melbourne Australia
Lines: 59

I have a basic question about subnet routing that has probably been asked
many times but I can't locate an answer in any article sitting around
here so ....

Is it possible to route between subnets of a class B address when the
subnets are separated by another network?

For example, given the following topology:

          +---------+
          | Host C1 |
          +---------+ 192.9.200.5
               |
       --------+-----+----- Net 192.9.200 ----------+---------
                     |                              |
               +----------+ 192.9.200.1        +----------+ 192.9.200.2
               | Gate GB1 |                    | Gate GB2 |
               +----------+ 137.147.1.10       +----------+ 137.147.2.20
                    |                              |
       ------+------+-------               --------+---+------
             |                                         |
        +----------+ 137.147.1.11                 +----------+ 137.147.2.21
        | Host B11 |                              | Host B21 |
        +----------+                              +----------+


       ^     Subnet 1 of 137.147    ^     ^       Subnet 2 of 137.147     ^
       |____________________________|     |_______________________________|

Host C1, and gateways GB1 and GB2 all connect to the one network - in this
example a class C network with number 192.9.200 (don't worry - we are not
actually using this number).

Gateways GB1 and GB2 are gateways to 2 subnets of the the class B
network 137.147 with subnet mask 255.255.255.0. There is no connection
between the two subnets except via 192.9.200.

The question is does this work?

Can hosts on either subnet route to hosts on the other (e.g. B11 <-> B21)?

Can hosts on either subnet route to host C1?

Can C1 route correctly to both B11 and B21?

Can other networks gatewayed onto 192.9.200 successfully route to hosts
on the 137.147 subnets?

If it works is there anything special I have to do to the gateways?

If this works a *lot* of IP addresses can be saved.  If this doesn't work
the only alternative appears to be to get a class B address for each
subnet (since they have up to 1000-2000 PC's each).

Any help would be much appreciated.

--------------
Murray Andrews
Telecom Australia Research Labs. (m.andrews@trl.oz.au)