[dhcwg] Re: mboned: draft-jdurand-assign-addr-ipv6-multicast-dhcpv6-00 comments

Stig Venaas <Stig.Venaas@uninett.no> Sun, 01 August 2004 18:10 UTC

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Date: Sun, 1 Aug 2004 19:44:09 +0200
From: Stig Venaas <Stig.Venaas@uninett.no>
To: Pekka Savola <pekkas@netcore.fi>
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Subject: [dhcwg] Re: mboned: draft-jdurand-assign-addr-ipv6-multicast-dhcpv6-00 comments
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On Sun, Aug 01, 2004 at 06:03:48PM +0300, Pekka Savola wrote:
[...]
> have RFC3306 or embedded-RP; it is not clear which problem we're solving
> (and which problems remain to be solved).
> 
> In particular, if any host on a link with a /64 prefix could calculate its
> own multicast prefix (unique to that link) on its own, and have 32 bits of
> group-id's to pick from (making sure they don't conflict on that link),
> could one argue that there is no need for central multicast address
> assignment.. but rather a mechanism where the host could pick a group-id in
> such a way it doesn't conflict (a random process should be sufficient, but
> if not, there could be Multicast DAD)?

Yes, I've also thought a bit about this. The 64-bit link-id could be a
starting point too. I think some form of DAD would be nice. It must also
be possible for a host to have multiple groups.

> Similarly, if embedded-RP is used, what you could need is the information
> what is the address of the RP or which prefix one should use for picking the
> multicast addresses.
> 
> So, looking at from a different perspective, it would seem that we don't
> necessarily need DHCPv6 for address assignment itself, but maybe some other
> configuration mechanism to figure out the multicast prefix which belongs on
> the link.

Yes, sounds good. So question then is whether DHCP or something else
should be used. WRT Embedded-RP I think allocating a prefix to the link,
as you suggest, is better than telling the application what the
Embedded-RP address is (applications shouldn't need to know about
Embedded-RP details).

I see some possible issues. There might be a need for giving hosts
different prefixes for different scopes (you could imagine having
one prefix where simply the scope bits are set to whatever scope
is needed). I think there are cases where you might use say
Embedded-RP internally (with small scope) and prefix-based addressing
externally (with larger scope) or vice versa. Or where you may want
different RPs for different scopes.

Well, in short, I also think the fact that we only need uniqueness
per link, should simplify things quite a bit. I would be happy to
work on possible solutions to this.

Stig

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