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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.unix.questions
Subject: Re: Multicasting
Message-ID: <17505@sun.uucp>
Date: Tue, 28-Apr-87 06:06:16 EDT
Article-I.D.: sun.17505
Posted: Tue Apr 28 06:06:16 1987
Date-Received: Thu, 30-Apr-87 00:40:54 EDT
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>   Is multicasting support at the Un*x socket level (preferable STREAM
> sockets) or by some other "device" on SUN-3s?

No.

Consider, for example, that if you want a stream socket, that would pretty
much mean a TCP socket here.  (Note to those confused by the word
STREAM here - it refers neither to STREAMS as implemented in System V
Release 3 nor to "Extensible Streams" as implemented by Apollo.
"stream" is a horribly overloaded word....)

Doing a multicast version of a protocol like TCP would be a bit messy
(note that neither 4.2BSD nor 4.3BSD, for example, implement
broadcast TCP).  You would have to support what amounted to a
connection to the given port on each host in the multicast group.
Since the receiving host can decide whether it wants to belong to a
multicast group or not, this would be rather tricky....

Even with UDP (which supports broadcast in the 4.[23]BSD
implementations), you would need to make extensions to current IP
implementations to support multicasting.  There are such extensions
proposed - see RFC 966 and RFC 988 - but they are not, as far as I
know, widely implemented.  It's certainly not implemented in the
4.2BSD TCP/IP code upon which our TCP/IP code is based.

You'd have to get to the raw Ethernet level to do multicasting, and
we don't currently happen to support multicasting.  I don't know
whether we ever will.