Subject: [MOBILE-IP] Multicast join of MN who is using FA COA via a local multicast router

From: "Lee, Jiwoong" <[email-masked]>
Date: Fri, 22 Sep 2000 23:18:26 +0900

Dear all in Mobile IP WG.

According to RFC2002bis-03, an MN who is using a foreign agnet
care-of address MAY join a multicast group, via a local multicast router.
(FA does not have to be this multicast router.)

If this local subnet uses a shared medium such as Ethernet, this make sense
enoughly.  MN will be able to listen the Mulitcast Router Advertisement
message and will generate an IGMP reply message to that link.
The Multicast Router will hear of this reply, and start to forward requested
multicast traffic to that link (actually to the related interface), without
regard to the source address of MN's IGMP reply message.
(I guess therefore RFC2002bis-03 declares that MN MAY use its home
address as the source IP address of its IGMP message.)

If the local subnet uses point-to-point links such as 3G cellular network,
where FA is the subnet edge router and establishes PPP sessions with
MNs, the scenario just described above will NOT work. The only possible
case is that the FA is a multicast router.)

I believe that one of the next three statements should be included in the
next version of RFC.

 - FA is assumed to be a multicast router
 - MN using FA COA cannot join a group via a local mulitcast router
   in a point-to-point linked subnet
 - or somewhat else.

Comments please.

Goodday,
Jiwoong Lee

PS.
----------------------------------------------
4.4. Multicast Datagram Routing (bis-03)

   [...]
   First, a mobile node MAY join the group via a (local) multicast router
   on the visited subnet.  This option assumes that there is a multicast
   router present on the visited subnet.  If the mobile node is using
   a co-located care-of address, it SHOULD use this address
   as the source IP address of its IGMP [8] messages.
   Otherwise, it MAY use its home address.