Subject: Re: [MBONED] IPv4/IPv6 Multicast interoperability

From: Stig Venaas <[email-masked]>
Date: Tue, 11 Sep 2007 14:07:03 +0200

Vincent Gay wrote:
> Hi all,

Hi Vincent. I've been planning to follow up on this for a while,
apologies for the late response.
> 
>  
> 
> I and my company are strongly interested in doing efficient Multicast
> over IPv4 between IPv6 islands.
> 
> Ideally, any host, in v4 or v6 domain, should be able to receive
> Multicast stream content sourced by any other host. Note that Multicast
> stream must be sent in Multicast over both IPv4 and IPv6.
> 
>  
> 
> I saw that a set of solutions  - based on reflection or translation -
> had been implemented some years ago (respectively by K.Kabassanov and
> S.Venaas).

For this particular problem I think encapsulation is better than
translation. Sounds like more or less need to map IPv6 multicast
groups to IPv4 groups and encapsulate the IPv6 multicast into the
respective IPv4 multicast groups. There are some interesting questions
whether this should be 1-1 etc.

There has been some work somewhat related to this. See for instance
draft-ietf-l3vpn-2547bis-mcast-05.txt which has some interesting
discussion on different types of mappings depending on what you want
to optimise etc. I think the l3vpn stuff could apply to what you are
doing, although I have a feeling that things could be much simplified
for a barebones solution doing just what you need.

One example of a solution pretty much like what you want is
draft-xu-softwire-4over6multicast-00.txt, except that this is IPv4
islands being interconnected with multicast in an IPv6 backbone.

> Has anyone here an update about where you stand for IPv4/IPv6 Multicast
> Interoperability? What is the current state of art?

There has been very little work on this that I know of. I think this is
an interesting topic. We're likely to have IPv4 and IPv6 deployed
together for quite a few years to come and I'm sure there will be some
need for multicast interoperability as well. So far there has been very
little demand or requests for it though.

Stig

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From: Stig Venaas <[email-masked]>
Date: Tue, 11 Sep 2007 14:07:03 +0200

Stig

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From: "Manfredi, Albert E" <[email-masked]>
Date: Tue, 11 Sep 2007 11:24:12 -0400

> -----Original Message-----
> From: Stig Venaas [mailto:[email-masked]] 

> little demand or requests for it though.

My immediate reaction would also be to use encapsulation in these cases
of IPv4 or IPv6 islands. But what about the dual-stack cases? Has there
been any thought to doing something in multicast that's similar to the
"IPv4 mapped IPv6 address", described in RFC 4291 and 4038?

Bert

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From: "Manfredi, Albert E" <[email-masked]>
Date: Tue, 11 Sep 2007 11:24:12 -0400

Bert

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From: Tim Chown <[email-masked]>
Date: Thu, 13 Sep 2007 11:50:40 +0100

> "IPv4 mapped IPv6 address", described in RFC 4291 and 4038?

These addresses aren't (or shouldn't be) seen on the wire though.
 
What exactly are you suggesting?

-- 
Tim

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From: Tim Chown <[email-masked]>
Date: Thu, 13 Sep 2007 11:50:40 +0100

-- 
Tim

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From: "Manfredi, Albert E" <[email-masked]>
Date: Thu, 13 Sep 2007 10:29:23 -0400

> From: Tim Chown [mailto:[email-masked]] 

> What exactly are you suggesting?

Actually not dual stack. I'm wondering if one couldn't develop a form of
IPv6 multicast address that would facilitate an IPv4-only multicast
source communicating to IPv6-only multicast clients. Or the other way
around should be possible too, with obvious restrictions.

Bert

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From: "Manfredi, Albert E" <[email-masked]>
Date: Thu, 13 Sep 2007 10:29:23 -0400

Bert

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From: Marshall Eubanks <[email-masked]>
Date: Thu, 13 Sep 2007 10:53:29 -0400

If you had a dual stack RP, then IPv4 <--> embedded RP IPv6 would be  
straightforward.

The embedded RP group ID is 32  bits. If the group ID 32 bits came  
from 224/4 (i.e., had the first 4 bits as 1110), then the dual stack  
RP could

- create and send an IPv6 embedded RP group address packet for each  
IPv4 packet received and
- take each incoming IPv6 embedded RP group packet and put it on the  
wire as the corresponding IPv4 packet.

This would of course require further carving up the IPv6 embedded RP  
multicast address space, though. This could be
automatic, or the last remaining flag could be used to signify it (on  
the IPv6 side).

Regards
marshall

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From: Marshall Eubanks <[email-masked]>
Date: Thu, 13 Sep 2007 10:53:29 -0400

Regards
marshall

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From: Stig Venaas <[email-masked]>
Date: Thu, 13 Sep 2007 18:49:04 +0200

Marshall Eubanks wrote:
> The embedded RP group ID is 32  bits. If the group ID 32 bits came from 
> 224/4 (i.e., had the first 4 bits as 1110), then the dual stack RP could
> 
> - create and send an IPv6 embedded RP group address packet for each IPv4 
> packet received and

This is more or less what I did in the translation gateway that was
mentioned earlier. There could be several gateways with different IPv6
addresses, each with some /96 prefix based on embedded-RP and the 32 bit
group ID the IPv4 address. You then pick which gateway to use by
choosing which embedded-RP address you use. I'm not convinced there
need to be any standard way of doing this.

I should add though that one should avoid translation if possible. There
are several issues regarding translation, just like there is for unicast
translation.

Stig

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From: Stig Venaas <[email-masked]>
Date: Thu, 13 Sep 2007 18:49:04 +0200

Stig