At 01:23 PM 4/22/00 , Johnny Billquist wrote:
>On Sat, 22 Apr 2000, Matt Thomas wrote:
>
> > At 02:20 AM 4/22/00 , Johnny Billquist wrote:
> > >Well, no. Multicast is an IP term. In ethernet, all addresses with a "1"
> > >in the low bit of the first byte is a broadcast, since that is the
> > >broadcast bit.
> > 
> > Bzzzt.  Wrong.  Multicast is a Ethernet term.  Ethernet controllers have
> > *multicast* filters.  The broadcast address is a special multicast address.
> > MOP uses multicast addresses (MOP Dump/Load uses AB-00-00-01-00-00 and 
> > MOP Remote Console uses AB-00-00-02-00-00).
>
>Certainly not. The DELUA that I'm using don't think that all ones is any
>special at all. I have to list that one just like any other broadcast
>address that I want to listen to.

Damn.  That means all the time I was at Digital, we must have been wrong 
about the terminally.  DECnet didn't use multicast addresses, it used broadcast.
Too bad we can't go back and all the specificiations.  Ditto for LAT, LAVC,
MOP, LAD, LAST, and all of other LAN protocol.  And ISO has made the same mistake
with ISO ESIS.  

And when I was responsible for the official list of DEC assigned protocols and
multicast addresses, we named that wrong as well.

Heck, we in the IETF screwed up too when we had IPv6 Neighbor Discovery use
multicast addresses as well.

> > >It is, however, up to every machine to decide which broadcast you want to
> > >receive (inlcuing the all-ones).
> > 
> > Again you have the sense of multicast and broadcast reversed.
>
>Nope. IP, however have both broadcast and multicast.

Correct.

>The IP address 255.255.255.255 is a broadcast address that goes to every
>machine on the same network. Broadcast addresses on the other hand are
>class D addresses, which are 224.x.x.x to 239.x.x.x

Remember that Ethernet and IP were developed independently at different times.
In fact, you meant multicast in the second sentence there.  IP multicast address
map to Ethernet (or IEEE 802) multicast addresses.  Look at the RFC if you don't
believe me.

>All machines talking IP have to know about 255.255.255.255, but they don't
>have to know anything about multicasts.

Bingo.  Becuase they send to the Ethernet Broadcast Address, which is defined
in the DIX Ethernet spec (remember that the D stands for Digital) as FF-FF-FF-FF-FF-FF.
All address where the first bit in the destination address on the wire
is defined as multicast (aka bit 0 of the first octet in the destination address) but
in the DIX only one multicast was defined, the broadcast address.

Seriously, I would advise you to go back and check the facts.  I spent 10+ years
as the primary developer of the datalink interface in ULTRIX and Digital UNIX as well
at LAT, DECnet, OSI, and other protocols.  I spend a lot of my writing LAN drivers
for NetBSD.  I may be wrong on this but I wouldn't count on it.
-- 
Matt Thomas               Internet:   matt@3am-software.com
3am Software Foundry      WWW URL:    http://www.3am-software.com/bio/matt/
Cupertino, CA             Disclaimer: I avow all knowledge of this message