Subject: [mobile-ip] RE: MIPv6 draft 18 - MIP and multicast

From: "Alan O'Neill" <[email-masked]>
Date: Fri, 12 Jul 2002 19:31:09 -0400

Just a reminder that this draft is available at;
http://www.flarion.com/technology/draft-oneill-mip-multicast-00.txt.

In the context of the review of -18 I would propose`that the multicast text
only cover the reverse tunnelling case and leave new work to cover the
foreign multicast case because I think there is much work to do here. This
is I think reasonable given the lack of discussion and consensus on this
issue. The other option is just to include the hybrid model only (reception
via foreign multicast but origination via the home multicast system as a
non-member system) because this option does not impact multicast routing
protocols and is simply an MIP routing issue.

I am happy to provide suitable text to cover either option..or in fact to
work within a group to try to come up with solid recommendations in this
area for the document.

Alan.

-----Original Message-----
From: Alan O'Neill 
Sent: 08 July 2002 18:16
To: [email-masked]
Subject: MIP and multicast

I have just submitted an internet-draft (abstract below) on the subject of
MIPv4 and MIPv6 multicast support via the Foreign multicast system which
will be available at http://www.flarion.com/technology/tech_standards.html
hopefully early this week.

Both MIPv4 and MIPv6 presently require the MN to use a CCoA as a foreign
multicast source address. This I believe is problematic for multicast
protocols that build source specific trees at cellular mobility rates. This
is because each tree needs to be rebuilt on every hand-off which is going to
thrash the routing system because every router on each tree is being exposed
to the movement of every MN on that tree. Clearly, the more trees with MN
senders the worse this problem becomes. ASM (PIM-SM) and SSM (on any
protocol) all build source trees so I believe this is a major deployment
barrier for foreign network multicast.

In contrast, the HoA is stable across hand-offs and therefore this should be
the source address and also used to populate multicast forwarding entries.
To avoid the RPF check failing (expects packets from the HA and not the FA),
the draft discusses various ways to initially bypass the problematic RPF
checks, but in the future for multicast routing protocols to be evolved to
be able to support an arbitrary RPF point (the present Multicast Designated
Router of the MN). The RPF approach is optimal because each hand-off only
changes the RPF interface in routers local to the hand-off and is therefore
scalable. The draft does not however deal with the multicast changes in
detail but is simplky intended to motivate discussion, MIP spec changes and
appropriate multicast research and standards work.

I will be in Yokohama from sunday to wednesday afternoon and am happy to
discuss this with interested parties outside the main meeting.

Regards, Alan.

Mobility Management and IP Multicast  <draft-oneill-mip-multicast-00.txt>

Abstract
                 
   Mobile IP provides a mobile node, that visits a foreign subnet, the
ability 
   to continue to use an address from its home subnet (the home address) as
a 
   source address. This is achieved through the allocation of a Care of
Address 
   on the foreign subnet that is used as the end-point of a redirection
tunnel 
   from a home agent on the home subnet. Mobile IP in RFC 3220 states that
when 
   the mobile node originates multicast traffic intended for the foreign 
   multicast system, it can only do so by first obtaining an IP address from
the 
   foreign subnet (a Collocated Care of Address) and then using this address
as 
   the multicast source address. This is to ensure that the source address
will 
   pass multicast routing reverse path forwarding checks.

   This foreign multicast model is however extremely restrictive, and still
very 
   problematic to multicast routing and applications when the mobile node 
   regularly changes foreign subnets, as is common in wireless systems. This
is 
   because the source address continues to evolve which must be tracked by 
   source specific multicast application and routing signalling. Using the
home 
   multicast system, again described above, is also non-optimal because the 
   mobile node receiver is then serviced by packets that must be tunnelled
from 
   its home agent which, removes any multicast routing benefits (ie network 
   based tree building). This draft therefore describes modifications to the

   foreign multicast interface between mobile IP and multicast routing that 
   enable the mobile node to use its persistent home address as a multicast 
   source address.