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From: kwe@buit13.bu.edu (Kent England)
Newsgroups: comp.dcom.sys.cisco
Subject: Re: routing parts of a Class B
Message-ID: <64157@bu.edu.bu.ede>
Date: 12 Sep 90 16:17:58 GMT
References: <8560@fy.sei.cmu.edu>
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In article <8560@fy.sei.cmu.edu> tgp@sei.cmu.edu (Tod Pike) writes:

>...  I have a class B subnet being routed out one interface of my Cisco
>box.  A portion of my organization (who have a dedicated range of class C
>subnets of my network) would like to have their own wire.  I would like to
>route only their portions of my class B out a separate interface, leaving
>the rest of my numbers routed out the normal interface.

	I think you mean to say you have a class B with eight bits of
subnet.  I think you want to have a single class B network, two cable
segments, and an arbitrary number of eight-bit subnets on each cable,
but you don't really want to subnet any more than necessary to support
the two cable segments.

	You can't have a single class B subnetted on one interface and
not subnetted on the other (from the point of view of the router).
The net is either subnetted or not.  If you subnet, you can layer
subnets on the same wire (interface) using cisco's secondary interface
capability.

	If you don't want to use subnetting in the router, but just
want two cable segments, you can place this router onto the net with
one interface and link the two ethernet segments together with an
external bridge and route IP.  This assumes the router is just an
interface to some external TCP/IP network.  Otherwise, run the router
as the bridge and don't route IP for your class B for now.

	I think you should plan on future subnets as you grow, so you
might decide to use secondary interfaces from the start, even though
it doesn't seem worth it right now.  At least assign host addresses as
though they might be subnetted in future.

	--Kent