Re: Multiple Class Cs on same physical network

Brian K. Jackson (bkjackson@tensar.com)
Wed, 18 Dec 1996 09:18:06 -0700

At 12:46 PM 12/17/96 +0000, you wrote:
>I have recently added a class C address to a network that already has
>a Class C address. Both class C addresses operate on the same
>physical network. (%95 of the addresses are virtual domains that are
>not very busy, so it isn't too crowded.. yet!)
>
>Anyhow, my name server is in the 205.206.213.0 network and I want to
>move all my PMs to the 206.75.140.0 network. Will the portmaster
>have any difficulties communicating with the other class c addresses
>in the network? Do I have to add any routing info in the PM or will
>just a default gateway to my cisco router suffice?
>
>I use routed on unix hosts and have set all PMs to have routing on.
>
>Any feedback would be appreciated.
>
>Regards,
>
>Pat
>
>

I played with this for several days. I wanted to get the pm to look up two
sets of noncontigious class c sets as local (arp cache lookups). However
there does not seem to be a way to add more then one sub/net route for the
local interface to the pm routing table. This means that in order for a pm
to utilize two (or more) class c sets on one physical cable plant, there
must be a router on that plant capable of recognizing the two address sets.
Which in turn means that for every packet which crosses the class c
boundries you get double the packets. One packet addressed to the router,
the router then sees that the address is local and transmits the same packet
over the same physical cable plant with the new destination address. I did
not try adding host routes for one set of the class c. I assume this will
work, but I know I don't want to add all those routes or maintain em.

Even the most simple minded pc routing can have more then one sub/net route
for the local interface. Why you can't do this on the pm is beyond me. So
what do you think MR. Livingston? Why can't I do this?

What I ended up doing is assigning the pm interface address from the same
set that the radius and name server are on. Then the inbound dialups are
assigned from whichever set makes the most sense for the particular user.
The problem here is that since there is only one address for the pool (set
assigned_address) only one set of these addresses can be dynamically
assigned. The other set must be statically assigned.

---
Brian K. Jackson         who?   bkjackson@tensar.com
Tensar Inc.              what?  Software Engineering & Consulting Services
Salt Lake City, Utah     where?