you know, Leigh Anne, I recall seeing a CAM table in one of the documents I
checked while I was researching you question. check out
http://www.cisco.com/warp/public/473/22.html
if you scroll down about half way, and look over the CAM table. Lo and
behold, the spanning tree, CGMP, and CDP MACs are there, appearing in each
of the vlans. there are a couple of other suspicious looking MACs there as
well, but I can find no information referencing them. oh wait. Cisco shared
spanning tree = 01-00-0c-cc-cc-cd
still can't find a reference for 01-00-0c-ee-ee-ee
Chuck
-----Original Message-----
From: Leigh Anne Chisholm [mailto:[EMAIL PROTECTED]]
Sent: Saturday, September 01, 2001 1:04 PM
To: Chuck Larrieu; [EMAIL PROTECTED]
Subject: RE: Multicasting - means what? [7:18232]
Heck no Chuck... I don't mind you bringing it up. I think it's an
interesting discussion. If you hadn't, and hadn't provided me with the
information for me to remember the correct answer, I would have posted it.
At any rate... with respect to your public and private emails to me:
When CGMP is enabled on a switch, the switch adds the MAC address
01-00-0C-DD-DD-DD to its "cam system" table. By default, a switch only
listen to multicast addresses in show cam system. I'd expect to see the MAC
multicast address for Spanning Tree to be in there as well as you suggested
in the private email.
I believe that 01 is reserved for all multicast addresses. It's just that
01-00-5E-00-00-00 through 01-00-5E-7F-FF-FF have been reserved for IP
multicast translation as you said in a private email to me. I don't think
anyone's been playing "fast and loose" with this one. Just you and I had a
blonde moment.
Don't know about the Token Ring address for sure... I've **GOT** to get
working on my current project because I'm **WAY** behind. But if you read
it right to left, I see the first octet as 01...
-- Leigh Anne
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> Chuck Larrieu
> Sent: Sunday, September 02, 2001 9:48 AM
> To: [EMAIL PROTECTED]
> Subject: Multicasting - means what? [7:18232]
>
>
> 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=18263&t=18232
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