Subject: RE: mboned: RE: WGLC for draft-ietf-mboned-routingarch-06.txt

From: Pekka Savola <[email-masked]>
Date: Mon, 6 Nov 2006 14:20:37 +0200 (EET)

On Tue, 31 Oct 2006, Manfredi, Albert E wrote:
> > > 3. In Section 2.7.2 -
> > > 
> > >   'IEEE 802.1D-2004 specification describes Generic Attribute
> > >    Registration Protocol (GARP), and GARP Multicast Registration
> > >    Protocol (GMRP) [GMRP] is a link-layer multicast group 
> > application of
> > >    GARP that notifies switches about IP multicast group memberships.
> 
> I just noticed this. Is that statement correct? GMRP doesn't really know
> anything about IP multicasts, right? It's MAC multicasts that it
> concerns itself with, yes?

Could someone with better knowledge of the spec comment on this?

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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From: Jean-Jacques Pansiot <[email-masked]>
Date: Mon, 06 Nov 2006 18:11:24 +0100

> Could someone with better knowledge of the spec comment on this?
Well,  802.1D-2004 is about the Mac Layer, nothing about network/IP layer.
It is up to the  receiver (kernel ?) to translate an IP multicast 
address (following
an add_membership at the socket level) into the corresponding mac 
multicast address,
in order to register (equivalent to an IGMP report)
All GMRP messages use Mac addresses to identify groups.
No snooping in bridges, so it looks cleaner,
but you have to add code in end stations :-((
and you still need IGMP reports (so 1 join = 1 IGMP + 1 GMRP message)
The only mention of IP multcast in the spec is that it is an open model
(you dont need to register in order to send) :

IETF RFC 2236, Fenner, Internet Group Management Protocol (IGMP), 
Version 2, November 1975

note that the quoted version of IGMP seems quite old :-))

Hopes this help

Jean-Jacques

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From: Pekka Savola <[email-masked]>
Date: Mon, 6 Nov 2006 19:19:51 +0200 (EET)

On Mon, 6 Nov 2006, Jean-Jacques Pansiot wrote:
> Well, 802.1D-2004 is about the Mac Layer, nothing about network/IP 
> layer. It is up to the receiver (kernel ?) to translate an IP 
> multicast address (following an add_membership at the socket level) 
> into the corresponding mac multicast address, in order to register 
> (equivalent to an IGMP report) [...]

Yes, this is my understanding as well.  Anyone have a different 
opinion?

A slight editorial update of the spec ("notifies switches about MAC 
addresses corresponding to the IP multicast groups" or some such) 
might not hurt but not be completely required either.

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From: "Manfredi, Albert E" <[email-masked]>
Date: Mon, 6 Nov 2006 12:56:55 -0500

Pekka Savola [mailto:[email-masked]] wrote:

> Jean-Jacques Pansiot wrote:
> >

If used in conjunction with IP multicast, then I agree. Or IGMP snooping
can be used instead.

But the note perhaps should not imply that GMRP depends on a
"corresponding IP multicast group." In my view, these MAC multicast
registration protocols, i.e. GMRP or MMRP, are only interesting when
there is no IP multicast involved at all.

I might reword the 3rd paragraph of 2.7.2 like this (changes shown with
* on each side):

   IEEE 802.1D-2004 specification describes Generic Attribute
   Registration Protocol (GARP), and GARP Multicast Registration
   Protocol (GMRP) [GMRP] is a link-layer multicast group application of
   GARP that notifies switches about *MAC* multicast group memberships.
   *If GMRP is used in conjunction with IP multicasts, then the GMRP
   registration function would become associated with an IGMP "join."
   However, this GMRP-IGMP association is beyond the scope of GMRP.*
   GMRP requires support at the host stack and it has not been widely
   implemented.  Further, IEEE considers GMRP obsolete having been
   replaced by Multicast Multiple Registration Protocol (MMRP) that's
   being specified in IEEE 802.1ak [802.1ak].  MMRP is expected to be
   mainly used between bridges.  Some further information about GARP/
   GMRP is also available in Appendix B of [RFC3488].

Bert

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From: cao wei <[email-masked]>
Date: Tue, 07 Nov 2006 02:29:34 +0800

> there is no IP multicast involved at all.

IMHO, there is no real need to use GMRP with multicast. And I also want to know if there are interest with GMRP if without IP multicast.

Also personally I doubt if MMRP will be more successful than GMRP.
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From: John Zwiebel <[email-masked]>
Date: Mon, 6 Nov 2006 11:02:26 -0800

On Nov 6, 2006, at 10:29 AM, cao wei wrote:

> IMHO, there is no real need to use GMRP with multicast. And I also  
> want to know if there are interest with GMRP if without IP multicast.
>

FWIW: I was once on a project that use L2 multicast (ie not IP) so it  
-might-
have been able to take advantage of GMRP.

OTOH: the two reasons IP mcast wasn't used was because it wasn't yet  
ready for
prime time (ie, I'm talking about something many many years ago.   
Routers did
not support any multicast protocols at the time.)
  -and-
data had to be acked, something mcast still doesn't do.

But, in general, I agree.
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