Subject: [mobile-ip] minor issue w/ regards to MN use of MLD, must use link-local scope source address

From: "Ed Remmell" <[email-masked]>
Date: Mon, 18 Nov 2002 17:12:01 -0700

Hello,

Draft 19 of Mobile IPv6 says the MN SHOULD use a non-link-local scope source
address when sending MLD messages directly on a foreign link:

section 11.3.5. Routing Multicast Packets:
"In order to receive packets sent to some multicast group, a mobile node
must join that multicast group. One method by which a mobile node MAY join
the group is via a (local) multicast router on the foreign link being
visited. The mobile node SHOULD use one of its care-of addresses that shares
a subnet prefix with the multicast router, as the source IPv6 address of its
multicast group membership control messages."

This is incorrect. MLD requires a link-local scope source address in the MLD
message (in the newer drafts, this can also be the IPv6 unspecified
address). Otherwise, the MLD Report and Done messages that the MN sends to
the router on the foreign link must fail to validate.

>From the latest MLD draft (draft-vida-mld-v2-05.txt):
section 6.4.  Action on Reception of Reports:
"Upon reception of an MLD message containing a Report, the router checks if
the source address of the message is a valid link-local address, if the Hop
Limit is set to 1, and if the Router Alert option is present in the
Hop-By-Hop Options header of the IPv6 packet. If any of these checks fails,
the packet is dropped."

RFC-2710 has similar wording requiring validation by the router that the
source address of the MLD Report is link-local scope.

Thanks.
- Ed Remmell
Elmic Systems, USA
http://www.elmic.com

---

From: Jari Arkko <[email-masked]>
Date: Sun, 24 Nov 2002 16:46:30 +0200

Hi Ed,

> the router on the foreign link must fail to validate.

Right. I think the trouble we wanted to avoid in the MIPv6 text was
the use of the home address, which would have resulted in all kinds
of trouble in this case. However, we failed to observe the MLD rules
as you correctly point out. So, I agree that this is a problem.

I would like to propose that the text

    ... The mobile node SHOULD use one of its
    care-of addresses that shares a subnet prefix with the multicast
    router, as the source IPv6 address of its multicast group membership
    control messages.  The mobile node MUST NOT use the Home Address
    destination option when sending MLD packets [29]

be changed to simply say that

    ... The mobile node MUST NOT use its home address or the Home Addres
    destination option when sending MLD packets [29].

Jari