Subject: [mobile-ip] "running MLD"

From: Marc Hasson <[email-masked]>
Date: Mon, 13 Jan 2003 02:50:51 -0800 (PST)

I'd like the term "running MLD" clarified in the following excerpt from
10.4.2 since I think it can mean multiple things:

   The home agent MUST be capable of receiving tunneled multicast group
   membership control information from the mobile node in order to
   determine which groups the mobile node has subscribed to.  This
   involves running MLD [27] inside the tunnel using link-local
   addresses.

Looking at the mailing list references I believe "running MLD" was used
just to mean that the MN can issue standard Report (or Done) MLD
messages with a link-local source through the tunnel to the HA to
designate the groups of interest.  Is this all the above excerpt is
saying?   And after receiving that membership info does the HA forward
that same packet on to the home network after noting it itself?  What
about from the other direction?  Its not saying that the HA must be a
multicast router/querier?  Does the HA merely tunnel MLDs and multicast
data packets for subscribed MN groups from the home network to the MN?
Or does it have to initiate MLDs of its own either to the MNs or on
behalf of the MNs for true MLD queriers?

Also, do we need a note about HA forwarding MLD packets to/from the MN
that have a link-local scope multicast destination and a hop limit of
1?  Text later in the same paragraph as the above excerpt forbids the
former and based on pure IPv6 semantics a hop limit of 1, as mandated
by MLD, should not result in a packet being forwarded [over a tunnel].

   -- Marc --

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From: YOSHIFUJI Hideaki / 吉藤英明<[email-masked]>
Date: Mon, 13 Jan 2003 20:08:32 +0900 (JST)

> by MLD, should not result in a packet being forwarded [over a tunnel].

I raised similar concerns to editor at the last IETF in Atlanta.
IMHO, HAs do not forward any MLD pacets.  HA should act as multicast 
router / querier and run a sort of mutlicast routing protocol if a HA 
supports multicast forwarding.

-- 
Hideaki YOSHIFUJI @ USAGI Project <[email-masked]>
GPG FP: 9022 65EB 1ECF 3AD1 0BDF  80D8 4807 F894 E062 0EEA

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From: Francis Dupont <[email-masked]>
Date: Mon, 13 Jan 2003 13:44:22 +0100

=> I agree: the HA should never forward link-local packets. For MLD
it should be a multicast router, for DHCPv6 it should be a relay.

Regards

[email-masked]

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From: Henrik Petander <[email-masked]>
Date: Mon, 13 Jan 2003 16:46:58 +0200 (EET)

> it should be a multicast router, for DHCPv6 it should be a relay.

Yes, this is the right way to allow MN to participate in link local
protocols. It would allow HA to always act as a router instead of acting
as a bridge for certain kinds of traffic.  The exception to not forwarding
link local traffic should IMHO be removed.

BR,

Henrik Petander

		----------------------------------
		Henrik Petander
		Helsinki University of Technology,
		GO/Core Project
		[email-masked]
		Office: +358 (0)9 451 5846
		GSM: +358 (0)40 741 5248
		----------------------------------

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From: Alexandru Petrescu<[email-masked]>
Date: Mon, 13 Jan 2003 17:07:58 +0100

Marc Hasson <[email-masked]> writes:
> designate the groups of interest.

Along the lines of this discussion, let me bring forth another aspect
of the design space, related to Mobile Routers.  The MR connects a
"mobile network" composed of several "fixed" hosts to the Internet, it
runs Mobile IPv6, it changes its CoA, while fixed hosts don't see any
change in address.

In that case, a simple choice would be for MR to run a mc routing
protocol (not MLD which is naturally link-scoped) and for the LFNs to
run MLD between themselves and the MR.  Which says it might be less
preferable to have LFN-[MLD]-MR-[MLD]-HA and more preferable to have
                   LFN-[MLD]-MR-[mc routing protocol]-HA

Just a thought...

Alex

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From: Erik Nordmark <[email-masked]>
Date: Thu, 23 Jan 2003 06:10:59 +0100 (CET)

> supports multicast forwarding.

Do you know if it can do that when the home link is physical?

I'm concerned about the HA having the correct RPF checks for both
the MNs away from home and the rest of the home subnet.
Does this mean that the HA will need to inject a host route into
the multicast routing protocol for each MNs away from home 
for the RPF checks to work? Or is this a local problem on the HA?

If it works, great. I'm just not certain it does.

  Erik