Subject: Question on MLD

From: Siva Veerepalli <[email-masked]>
Date: Thu, 27 Feb 2003 11:23:07 -0800

RFC2710 (MLD) states that when a General Membership Query is received, a 
node listening to the query sends a membership report for all multicast 
addresses it is listening to, excluding the all-nodes link-local multicast 
address and any multicast addresses of scope 0 (reserved) and 1 (node-local).

My question is, is the node required to send the membership report for 
solicited-node multicast address as well? In general, since nodes do not 
receive link-local scope multicast packets from out side the link, why is 
it required for the nodes to report membership to the router for *any* 
link-local scope multicast addresses?

Thanks,
Siva

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From: Brian Haberman <[email-masked]>
Date: Thu, 27 Feb 2003 14:32:14 -0500

MLD-snooping switches is the biggest reason.

Brian

Siva Veerepalli wrote:
> addresses it is listening to, excluding the all-nodes link-local 
> multicast address and any multicast addresses of scope 0 (reserved) and 
> 1 (node-local).
> 
> receive link-local scope multicast packets from out side the link, why 
> is it required for the nodes to report membership to the router for 
> *any* link-local scope multicast addresses?
> 
> Thanks,
> Siva
>

---

From: Siva Veerepalli <[email-masked]>
Date: Thu, 27 Feb 2003 12:00:52 -0800

>MLD-snooping switches is the biggest reason.

Ok. So, it seems like there would be no need to send these reports for 
link-local multicast on point-to-point links. Should this clarification be 
made in the IPv6 over PPP RFC?

thanks,
Siva

>>multicast address and any multicast addresses of scope 0 (reserved) and 1 
>>(node-local).

---

From: Brian Haberman <[email-masked]>
Date: Thu, 27 Feb 2003 15:18:19 -0500

Siva Veerepalli wrote:
> link-local multicast on point-to-point links. Should this clarification 
> be made in the IPv6 over PPP RFC?

How many implementations of MLD pay attention to the link-type
of the interface?  All the MLD codebases that I have seen are
interface-type agnostic and treat them all the same.  I don't
see the benefit of revving RFC 2472 to change this behavior.

Regards,
Brian

---

From: Greg Daley <[email-masked]>
Date: Fri, 28 Feb 2003 09:15:10 +1100

Hi Siva,

RFC 2462 says that the node MUST join the solicited-node
multicast group (which implies using MLD) when performing
DAD.

Since the node has to send an MLD report in the first
instance, there's no reason not to follow the rest
of the MLD specification.

Greg

Siva Veerepalli wrote:
>>> RFC2710 (MLD) states that when a General Membership Query is 
>>> received, a node listening to the query sends a membership report for 
>>> all multicast addresses it is listening to, excluding the all-nodes 
>>> link-local multicast address and any multicast addresses of scope 0 
>>> (reserved) and 1 (node-local).
>>> My question is, is the node required to send the membership report 
>>> for solicited-node multicast address as well? In general, since nodes 
>>> do not receive link-local scope multicast packets from out side the 
>>> link, why is it required for the nodes to report membership to the 
>>> router for *any* link-local scope multicast addresses?
>>> Thanks,
>>> Siva

---

From: Markku Savela <[email-masked]>
Date: Fri, 28 Feb 2003 00:31:03 +0200

> multicast group (which implies using MLD) when performing

Presumably it needs to do the MLD join with ::-src address, because
before DAD address is not yet valid.

Personally, I think the spec is just plain wrong. I believe one should
not use MLD on link local multicast groups.
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From: Brian Haberman <[email-masked]>
Date: Thu, 27 Feb 2003 18:02:40 -0500

> before DAD address is not yet valid.

That is exactly what draft-ietf-magma-mld-source-04.txt is
intended to correct.  That draft is in front of the IESG at
this time.

> not use MLD on link local multicast groups.

As I pointed out in an earlier message, MLD messages are necessary
in order to deal with MLD snooping switches.

Brian

---

From: Greg Daley <[email-masked]>
Date: Fri, 28 Feb 2003 10:27:12 +1100

Hi Markku,

> before DAD address is not yet valid.

Yes.  Currently there is a MAGMA draft describing this.
draft-ietf-magma-mld-source-04.txt

> not use MLD on link local multicast groups.

This is similar to the previous discussion on MLD-snooping switches.

Essentially the role of joining a multicast group is to create
state in the network.  With non-local multicast groups this has an
effect on routing infrastructure.

If MLD snooping switches are a likelihood in future networks,
then I think it is reasonable that nodes joining a multicast group
create state for them, whether the packets are link-local or
have greater scope.

In the mean time it is a requirement which is widely ignored
by implementors.

Greg Daley

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From: "Konstantin KABASSANOV" <[email-masked]>
Date: Fri, 28 Feb 2003 08:52:24 +0100

Hi,

In particular this kind of messages can be useful for mld snooping
switches.

Konstantin 

_____________________________________________________

Konstantin K. KABASSANOV 
Research and Development Engineer

LIP6 Laboratory
Pierre and Marie Curie University

8, rue du Capitaine Scott,
75015 Paris, France

Phone: +33 (0) 1 44 27 71 26
Fax:   +33 (0) 1 44 27 74 95

E-mail: [email-masked]
Web: http://www.kabassanov.com
______________________________________________________

> -----Original Message-----
> From: [email-masked] [mailto:owner-
> [email-masked]] On Behalf Of Siva Veerepalli
> Sent: jeudi 27 février 2003 20:23
> To: [email-masked]
> Subject: Question on MLD
> 
multicast
> receive link-local scope multicast packets from out side the link, why
is

---

From: Francis Dupont <[email-masked]>
Date: Fri, 28 Feb 2003 11:08:02 +0100

In your previous mail you wrote:

   
=> I fully agree and my old code always sent the first MLD reports from
the unspecified address. I never see an issue there (MLD report is one
of the third cases of unspecified sources with DAD and early RS). And
snooping switches are *great* when you have multicasts on a mixed speed
Ethernet (which is near always the case, unfortunately they don't snoop
MLD (i.e., they support only IPv4/ICMP) today).

Thanks

[email-masked]