Path: utzoo!mnetor!uunet!husc6!rutgers!mcnc!decvax!ucbvax!UMN-REI-UC.ARPA!slevy
From: slevy@UMN-REI-UC.ARPA (Stuart Levy)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: More than one IP (sub)network on one ethernet cable
Message-ID: <8712192222.AA04523@uc.msc.umn.edu>
Date: 19 Dec 87 22:22:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 23

The reason we do it is something like this, in my opinion ...

  a)  Some of us want IP-router like isolation, so we either get a bunch
      of separate networks or we do subnetting.  Being good Internet citizens
      we're doing the latter.
  b)  Not all of us want to do subnetting (who needs a gateway for 3 machines).
  c) Not all of us can do subnetting (some implementations still can't).
  d)  All subnetting implementations available to us demand that ALL
      subnets on a net be of the same size.
  e)  We like to put separate groups in separate chunks of address space,
      with the idea that they can choose to become a subnet later
      without having to change all their IP addresses.
  f)  We have enough groups who might potentially become subnets that
      we want to allow for a couple of hundred at least, and so chose
      class-C subnetting on our class-B net.
  g)  The resulting subnets are too small to stuff all miscellaneous hosts
      in just one of them, even if we wanted to.  One or a few large
      subnets plus a lot of small ones would be nice but we can't get it.
      A hierarchy of subnets would be nice too, but we can't get that either,
      at least not if we follow the normal rules.

				Stuart Levy, slevy@uc.msc.umn.edu
				Minn. Supercomputer Center & U. of Minnesota