Path: utzoo!mnetor!uunet!husc6!mit-eddie!ll-xn!ames!pasteur!agate!saturn!eshop
From: eshop@saturn.ucsc.edu (Jim Warner)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: remote broadcasts
Message-ID: <2284@saturn.ucsc.edu>
Date: 9 Mar 88 15:59:09 GMT
References: <8803090102.AA06582@apptek3.istc.sri.com>
Reply-To: eshop@saturn.ucsc.edu (Jim Warner)
Organization: University of California, Santa Cruz
Lines: 13

There is no guarantee that any particular (sub)net that you're
sending to supports broadcasting.  This topic is discussed
in RFC1009, mostly in appendix A.  Briefly, the local gateway
may forward a "directed broadcast datagram", but not through
the interface that it came in.  A local gateway is permitted
to black hole a directed broadcast.  Presumably, there should
be a software switch.

It may be useful to remember that intermediate gateways may
not be able to determine if a particular IP address is a broadcast
address unless they know the local subnet mask.  Thus disgarding
directed broadcasts is always done by the gateway guarding the
destination net.