Path: utzoo!mnetor!uunet!husc6!bu-cs!kwe
From: kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England))
Newsgroups: comp.dcom.lans
Subject: Re: Subnetting
Message-ID: <22482@bu-cs.BU.EDU>
Date: 9 May 88 14:24:34 GMT
References: <358@halley.UUCP> <203@tekbspa.UUCP>
Reply-To: kwe@buit13.bu.edu (Kent England)
Followup-To: comp.dcom.lans
Organization: Boston Univ. Information Tech. Dept.
Lines: 38
Summary: Subnets are an important admin device

In article <203@tekbspa.UUCP> joe@tekbspa.UUCP (Joe Angelo) writes:
>
>But what about subnetting? ...
>Is subnetting just a nice admistrativia thing? 

Subnetting is not at all administrivia if you are trying to plug two
autonomous systems together.  An autonomous system is just an
administrative boundary between networks.  You may have many ASs
within your company or campus or the chief boundary may be between
your Network and the Internet.  If you have ever tried just plugging
some other ASs router onto your homogeneous Ethernet, you would have a
feel for the grief that you and the other system admin are in for.
You don't have to hide your own admin trivia behind one Class A/B
network address, but it sure makes life easier.

It might be smart to prepare for installing routers by subnetting
addresses while still interconnecting segments with repeaters and/or
bridges.  You can set up a Class B with pseudo-subnetting and, at some
convenient point, replace repeaters and bridges with real IP routers
without having to change addresses.  (Hosts that understand subnets
must be properly instructed about the true network architecture.
Hosts that don't understand subnets must always be fooled.  :-)

>Or does your local
>enet board not receive the packets, period? Or is it the high
>level software that ignores the packet? Does anything really ignore
>anything? 
>

If your network is not really subnetted (just looks that way), then
broadcasts are still heard everywhere, your net will still meltdown,
your local enet boards will still process tens of broadcasts per
second.  :-) Just setting up addresses to look subnetted is not
subnetting, not until you actually have subnet routing.

That's my view...

	Kent England, Boston University