Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!decwrl!ucbvax!FTP.COM!mrf
From: mrf@FTP.COM
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Hosts whose IP numbers end in 0........
Message-ID: <9008272341.AA26062@ftp.com>
Date: 27 Aug 90 23:41:27 GMT
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: support@ftp.com
Organization: The Internet
Lines: 34


The fact that has been overlooked in your reading of the Host
Requirements RFC (which I agree is wonderful) is which portions
of an IP address are which.  On a Class B network (the kind in
question) which is not subnetted, the last TWO (2) bytes of the
address are the host format.

	NN.NN.HH.HH   }  2 bytes of net and 2 of host.

If this address is 129.126.52.0, the net portion is 129.126 and the
host portion is 52.0 (or 3400 hex) which is in fact non-zero.  This
should therefore be a legal address on the net (in theory).  The
broadcast address on this net would be 129.126.255.255, and the
network address would be 129.126.0.0.  There would be no conflict
between these addresses and the host address of 129.126.52.0.

However, I am not surprised that this is rejected by several
implementations, and do not think that this would be advisable on a
class B network, because I do not think it would lend itself to later
subnetting.  The best thing for this person to do is to probably only
use the 2nd host byte (unless he will have over 254 machines) and
leave the first byte 0.  This will allow him to less painfully put in
subnetting later if necessary.  Or, decide now on what his eventual
network needs will be and start off with the correct values in place
for subnetting (i.e give every host in one building a host value of 
1.nn, another building or floor 2.nn, etc.).  This might also help
when network problems arise to make it easier to locate the failing
machine (just a suggestion).

Just because something is legal doesn't mean it works (and vice
versa). 

Margaret Forsythe, Technical Support Manager, FTP Software, Inc.
mrf@ftp.com       (617) 246-0900 x100        FAX: (617) 246-0901