Re: I-D ACTION:draft-hoon-mobileip-undad-00.txt

Hi Ed,

Thanks for the question,

Ed Remmell wrote:
>>The issue is when a router fails or comes up on a link
>>for the first time, it cannot build a list of which hosts
>>are already on the link.
>>There is no ND message where all hosts (or even large
>>groups of hosts) must respond, which can be used to rebuild
>>ND state.
> 
> 
> What about having the router ping ff02::1 (the link-local scope all
> nodes multicast address) from its link-local scope unicast address? That
> should cause each host on the link to send a NS to the router's
> link-local scope unicast address to resolve its MAC address, so that
> they can respond to the ping.

While it may be possible for the router to send
ICMP Echo Requests to hosts, some of the hosts
may not respond, due to firewalling for example.

The system described in the document needs to be able
to guarantee that it knows that an address is not in use
before it gives it away.

This means that the mechanism has to be tied to a
system required for all hosts to do (for example,
because they have an interest in doing it),
where responses are guaranteed even from hosts that
do not want to participate in the optimization.

ND is one of these systems, but doesn't work when
there's no initial state.
MLD is one of these systems, but is not yet fully
deployed (but that's getting better).

For either of these mechanisms to work, _every_ host
has to provide state information.

If the address isn't guaranteed unique,
then we may as well use Optimistic DAD :)

Greg