this post results from an off line conversation with someone regarding
multicasting. The original question follows:
someone said:
CGMP: Router sends CGMP multicast packets to the switches at a well known
multicast MAC address: 01-00-0C-DD-DD-DD.
Now by definition, if all multicast frames have a destination MAC address
beginning with "01-00-5E" - how does this address qualify as multicast? I
got this from http://www.cisco.com/networkers/nw99_pres/314.pdf a
networkers presentation.
I've found other documents that reference this MAC address--but is this
really considered a multicast address?
end of quote
let's see - unicast is intended for a single destination, broadcast is
intended for all destinations. does that mean that anything intended really
or potentially for more than one destination, but not all destinations, is a
multicast?
I have the distinct impression that some folks somewhere are playing a bit
fast and loose with definitions. Is the spanning tree reserved mac
01-80-C2-00-00-00 multicast? it can't be broadcast because it is not
destined for the FFFFFF mac. How about the token ring error monitor mac of
03-00-00-00-00-10 ( this is the ethernet form of the address, according to
my source )
Is CGMP really "multicast"? As opposed, maybe, to an ethernet frame placed
onto the wire ( or issued out all ports ) for a specific purpose? Cisco's
own definition of multicast, "Single packets copied by the network and sent
to a specific subset of network addresses" leaves a lot of wiggle room. is
Cisco talking about layer three "network" of layer two "network"? not that
Cisco's definition is necessarily related to industry standard definitions,
as we all know from the numerous discussions about OSI here.
Any comment? Are we counting angels again? :->
Chuck
P.S. I hope the person who brought this up in private correspondence doesn't
mind my posting here. I sanitized so as to protect the innocent, so to
speak. that person is a regular groupstudy participant, so will find out
what I have done sooner or later ;->
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=18232&t=18232
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