Subject: RE: IPv6 w.g. Last Call on "IPv6 for Some Second and Third Genera tion Cellular Hosts"

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Wed, 22 May 2002 13:43:18 +0200

Itojun,

  > >=> I've never seen that in any spec.
  > >I guess you are saying that it's needed for L2
  > >switches that snoop MLD messages to decide
  > >on mcast forwarding of mcast ethernet frames?
  > >
  > >If so, then we don't have this situation in 
  > >cellular networks. What we're dealing with is
  > >a p2p link with no multicast capability. 
  > 
  > 	even under the above situation, there's no such clause 
  > that permits
  > 	omission of MLD in RFC2710 (MLD).  if you have any 
  > reference please
  > 	let me know, i'm interested in knowing the rationale 
  > for the claim.

=> I don't understant :(. RFC2710 does not say that 
MLD MUST be implemented in all IPv6 nodes. There is 
no statement in any IPv6 document that says anything
equivalent. So our interpretation is that it is not
mandatory, it's optional. I don't think that the lack
of a clear statement saying 'MLD is mandatory' should
imply that it is mandatory. Mandated protocols are 
clearly stated in their respective RFCs (e.g. ICMPv6).

So when is MLD needed? I will copy a paragraph from
the intro of 2710:

   "The purpose of Multicast Listener Discovery (MLD) is to enable each
   IPv6 router to discover the presence of multicast listeners (that is,
                  --------------------------------------------           
   nodes wishing to receive multicast packets) on its directly attached
   links, and to discover specifically which multicast addresses are of
   interest to those neighboring nodes.  This information is then
   provided to whichever multicast routing protocol is being used by the
   router, in order to ensure that multicast packets are delivered to
   all links where there are interested receivers."

Note the underlined text. If no discovery is needed, because
the addresses are hard coded, then no MLD needed for those 
addresses. 
Makes sense?

Hesham

  > 
  > itojun
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---

From: Brian Haberman <[email-masked]>
Date: Wed, 22 May 2002 07:51:15 -0400

Hesham,

>    IPv6 router to discover the presence of multicast listeners (that is,

Take a look at the very last paragraph of section 5 of 2710.  It
states:

     MLD messages ARE sent for multicast addresses whose scope is 2
    (link-local), including Solicited-Node multicast addresses [ADDR-
    ARCH], except for the link-scope, all-nodes address (FF02::1).

That means that a host MUST send an MLD Report for all multicast
groups it joins except all-nodes.

Brian

---

From: [email-masked]
Date: Wed, 22 May 2002 20:58:49 +0900

>   IPv6 router to discover the presence of multicast listeners (that is,

	no, it doesn't make sense to me.  even for hardcoded addresses, there
	should be an MLD join packet issued from the listener.

	what i don't understand is why you are wanting to omit it.  for
	example, if 3G mobile node in the following diagram transmits MLD join,
	uptream router could suppress packet to the expensive wireless link for
	packet to ff02::blah.  i believe MLD support has benefit to the
	situation.

itojun

	router
	  |
	  |
	3G mobile node