Re: [DNA-BOF] BoF Last Call on DNA WG Charter.

[Alper Yegin <alper@docomolabs-usa.com>]

On 10/28/03 10:48 AM, "Bernard Aboba" <aboba@internaut.com> wrote:

>> If "the same link as before" includes a link that your host was attached a
>> while ago, the above statement is not always true. As Bernard and John
>> pointed out, DHCP case is safe as the network guarantees the configuration
>> during your lease. But in the case of IPv6 address autoconfiguration, nobody
>> is there to defend your address on your behalf while you are gone.
> 
> The same problem occurs with IPv4 Link-Local addresses.  Since the
> probability of conflict is relatively high, we had to recommend that a
> host awakening from sleep, attaching, etc. had to do DADv4 again.
> 
> The chance of conflict is much lower in the case of IPv6, so I'd ask
> whether we think that the same approach is still necessary.  It's quite
> costly, of course, so if it can be avoided that is a good thing.

This is a hard question. The probability of collision (p1) is somewhat not
low enough, hence the RFC 2462 requires use of DAD. Now we are talking about
the possibility of an address collision sometime after the address was
checked out to be unique (p2). This is even a lower probabibility, yet how
do we determine it is low enough to be negligible? Also, note that the p2 is
a function of the number of new IP addresses configured while the host was
not defending its IP address. This is higher in a network where the number
of hosts joining the network (i.e., mobility) is high.

Alper