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From: lars@spectrum.CMC.COM (Lars Poulsen)
Newsgroups: comp.protocols.tcp-ip,comp.dcom.sys.cisco
Subject: Re: Partial subnetting
Message-ID: <1991May17.165241.6862@spectrum.CMC.COM>
Date: 17 May 91 16:52:41 GMT
References: <=~P_0Q&@warwick.ac.uk>
Organization: CMC (a Rockwell Company), Santa Barbara, California, USA
Lines: 34

In article <=~P_0Q&@warwick.ac.uk> cudcv@warwick.ac.uk (Rob McMahon) writes:
>We have a class B address (137.205.0.0) for the University.  Currently the
>whole campus is running without subnets, with bridges between each department
>and the backbone, but we allocated the numbers such that we could later give
>each department its own subnet, and change the bridges for routers should it
>become necessary.
>
>... our first department ... actually wants to be split off with a router,
>...  Here was the plan (internet address/netmask):
>
>			    137.205.0.0/0xffff0000
>				      |
>				      |
>			 ----------------------------
>			 |                          |
>		      Bridge			 Router
>			 |  			    |
>              137.205.232.0/0xffff0000	 137.205.176.0/0xfffffc00
>
>It seems that to make this work the routing tables on the Unix hosts ought to
>have a netmask associated with each entry, but it's not there.

Briefly: Yes, it will not work, for the reason stated. The next
generation of IP routers will keep masks with routes at all times, but
the routing protocol software to distribute and manage such routes is
still not frozen solid enough to give to the unwashed masses (OSPF-2 is
in draft, and there is still a vocal minority that insists that "dual
IS-IS" MUST be supported).

Universally masked routes will also resolve the other thing that
"intuitively ought to work": Disjointed subnets.
-- 
/ Lars Poulsen, SMTS Software Engineer
  CMC Rockwell  lars@CMC.COM