Subject: mboned: Re: IPv6 link-scoped multicast

From: Pekka Savola <[email-masked]>
Date: Thu, 5 Aug 2004 02:57:37 +0300 (EEST)

On Thu, 5 Aug 2004, Myung-Ki Shin wrote:
> As for the issue #2,
> our main goal is to *generate* unique multicast addresses - /96
> automatically (like RFC 3306) without any fear of conflicts.

"Any fear" is subjective.  It is completely possible that a node 
might start to send an SSM stream to that particular multicast 
address.

> o Multicast source side
>    1. Link-local address
>      - FE80::a12:34ff:fe56:7890
>    2. Predefined/static group id
>      - Channel 1 -> 1
>    3. Source can get unique multicast addresses - /96
>      - FF32:00ff:a12:34ff:fe56:7890::/96
>    4. Session creation
>      - FF32:00ff:a12:34ff:fe56:7890::1
> o Multicast receiver side
>    1. Predefined/static group id
>      - Channel 1 -> 1
>    2. *Source discovery*
>      - LLMNR + predefined group id
>    3. Join
>      - FF32:00ff:a12:34ff:fe56:7890::1

So, the group ID appears to be communicated out of band.

What is the name of the session?  Why cannot the source check from
LLMNR whether such a session, or such an address under that session
does not already exist? (This is why I was stating that this kind of 
problems appear to be trivially solved as part of source discovery.)

Apart from that..

Can you provide a bit of details what you're actually obtaining from 
LLMNR?  Does the source register the address 
FF32:00ff:a12:34ff:fe56:7890::1 there, and just join to what you 
receive?

If so, there is really no requirement for embedding EUI64 on the
address, it's just something that's assumed to be reasonably unique.

A constructive suggestion: reword this spec to use the upper bits of 
FF02::/16, even embedding the EUI64 if you wish, and publish it as an 
Informational RFC if you think an RFC is really needed.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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From: Jerome Durand <[email-masked]>
Date: Thu, 05 Aug 2004 19:32:52 +0200

> might start to send an SSM stream to that particular multicast 

And remember you can take 1,000,000,000 addresses on the link keeping a 
probability below 1 over 1,000,000 that there is a collision. Therefore 
I think you should justify your proposal with something else (simplicity 
for example, or calculation method to avoid randomization...)

My concern is that we can always derive a multicast address from 
something. You seem to need these addresses and I would really like to 
see examples of applications.

> Informational RFC if you think an RFC is really needed.

I'd say FF12::/16 as FF0X::/16 are must be reserved by IANA right?

Thanks !

Jerome