Re: [DNA] [Issue 15] [Issue 16] DAD and MLD Interaction

[Erik Nordmark <erik.nordmark@sun.com>]

James Kempf wrote:
>

> When a link level event occurs indicating that the host has moved from one
> link to another, DNA requires the host to determine whether a change in IP
> link has occured by sending an RS. The DNA host SHOULD select one of its
> link local addresses that is in the "Confirmed" state (i.e. assigned to an
> interface) and utilize that as the source address on the DNA RS.

Doesn't this imply that if the host has moved to a new link, and the 
Confirmed address is a duplicate on that link, that the host might 
accidentally overwrite the neighbor cache entry for the existing user of 
that link-local address?

That would seem to defeat the purpose of DAD.

It is safer to, immediately when the link level event arrives, switch 
all Confirmed addresses to Optimistic.
Then if it turns out that the host didn't move, it can switch those back 
to Confirmed.
And if it turns out that the host did move, it can send the actual NS 
DAD probe for all the IP addresses it has (the existing link-local 
addresses, as well as any newly configured IP addresses).



> If the returned DNA RA indicates that the host has not moved to a new IP
> link, no further action is required for multicast addresses to which the
> host has subscribed.
> 
> If, on the other hand, the DNA RA indicates that the host has moved to a new
> IP link, the host MUST issue MLD [RFC3810] messages to the router for
> subscribed multicast addresses, including the
> Solicited_Node_Multicast_Address for any unicast addresses configured.

It actually needs to handle the Solicited node multicast addresses 
before starting any DAD procedure, to ensure that it will receive DAD 
messages when there are MLD snooping L2 switches.

   Erik