Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!fxgrp!mr-frog
From: mr-frog@fxgrp.UUCP (Dave Pare)
Newsgroups: comp.protocols.tcp-ip
Subject: BSD IP broadcast datagram fragmentation
Keywords: IP broadcast
Message-ID: <1032@fxgrp.UUCP>
Date: 26 Apr 89 22:01:17 GMT
Lines: 23

4.3 BSD, SunOS 4.0.1, and AIX 2.2.1 all arbitrarily disallow fragmented
broadcast IP datagrams.  Since they are all are apparently derived from
the same 4.2 code, this shouldn't be surprising.  However, the IP protocol
specification mentions nothing about such a limitation.

Line 141 of netinet/ip_output.c (4.3 BSD code) contains the offending
lines...

		/* don't allow broadcast messages to be fragmented */
		if (ip->ip_len > ifp->if_mtu) {
			error = EMSGSIZE;
			goto bad;
		}

So, the question is, why the limitation?  I no-op'ed the offending
lines of code and I was able to broadcast and receive larger datagrams
with no apparent difficulty.

Naturally I'm working on an ethernet, so my perspective will probably
be a little different.  But that brings up the question: how does
broadcast work in a non LAN environment?  Does anyone actually use it?

Dave