Re: [rfc2462bis issue 274] conflict between MLD and NS delay

[Brian Haberman <brian at innovationslab.net>]

Markku,

Markku Savela wrote:

> > From: Brian Haberman <brian@innovationslab.net>
>
> > > - desire to avoid packet storms upon booting many nodes simultaneously
> > 2710 accomplishes this by using message suppression.  If a node hears a
> > Report for the same group, it cancels the transmission of any pending
> > Reports it has for the group.
>
> Above will totally fail with ND multicast groups. Their design goal is
> that each host is only on one group. It is highly unlikely that
> listening would hear a duplicate join for the solicited node multicast
> address.
It is not a failure, it is just not useful for solicited-node multicast
addresses.  But, you also snipped a part of the note that pointed out
that ND and MLD were designed with differing techniques to deal with
reliability.

> I've already said my differing opinion on this way back earlier, but
> apparently I lost the vote. But, just to make clear:
>
>   sending MLD messages for link local multicast groups is waste of
>   time and specification effort. If you have layer 2 sniffers, they
>   can (and most likely must) sniff the normal ND traffic too. A ND DAD
>   contains exactly the same information content as MLD join for the
>   solicited node group.
And the MLD Report for the solicted-node multicast address will cause
the L2 sniffer to forward the ND DAD message to any other port that
has joined the same multicast group.  If two nodes are DAD'ing for the
same unicast address, the L2 sniffer will need to forward those NS
messages to all ports where the solicited-node address has been joined.

Regards,
Brian

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