Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!magnus.ircc.ohio-state.edu!csn!boulder!daemon
From: jeff@NMSU.Edu (Jeff Harris)
Newsgroups: comp.dcom.sys.cisco
Subject: Sub-Netting Help
Message-ID: <33069@boulder.Colorado.EDU>
Date: 8 Mar 91 01:01:52 GMT
Sender: daemon@boulder.Colorado.EDU
Lines: 58

At NMSU, we currently have most of our ethernet segments connected to a 
backbone using filter repeaters (MAC layer bridges).  We are inerested 
in replacing those with routers as funds permit.  The question is how to 
phase in the movement from bridges to routers.  We have always given 
different buildings a range of IP's consistant with Class C subnetting, 
so our current environment looks like this:

         128.123.1.x                128.123.2.x
             |                          |
           MAC Bridge              MAC Bridge                     
             |                          |          
----------------------------------------------------128.123.x.x
             |                          |
           MAC Bridge              MAC Bridge                     
             |                          |
        128.123.3.x               128.123.4.x

As we break the backbone into pieces, our system might look like this:

         128.123.1.x                128.123.2.x
             |                          |
           MAC Bridge              MAC Bridge                     
             |                          |          
---------------------| Router |----------------------
             |                          |
           MAC Bridge              MAC Bridge                     
             |                          |
        128.123.3.x               128.123.4.x

No we have the problem of what the routing tables look like for the 
various machines.  The machines that are attached are mainly Suns and 
PCs, with a few VAXes and other things thrown in for good measure.  And 
while only four segments of 128.123 are shown there are actually 30 
segments involved.

Do we tell each machine that it is on a Class C network?  If so, do we 
have to statically assign routes for each subnet (since there are not 
real routers between all segments to provide routing info)?  Is there 
someway to tell the router that there are multiple Class C network on 
each interface?  That seems to be the easiest since RIP information 
would be consistant. If the latter is possible, what happens to a packet 
from 128.123.1.x to 128.123.3.x?  Is it actually handled by the router, 
our will the Suns send it between themselves as would be desired?

Has anyone else tried this that can provide some do/don't's etc?  Any 
help would be appreciated.

Thank you
Jeff Harris
Network Manager
Computer Center - Room 133E
Box 30001 / Dept 3AT
New Mexico State University
Las Cruces, New Mexico 88003-0001

Internet: jeff@NMSU.Edu                         Voice   : (505) 646-5110
UUCP    : sun!sunpeaks!sunnmex!nmsu!jeff        FAX     : (505) 646-5278
Bitnet  : jeff@nmsu