Re: A common problem with SLAAC in "renumbering" scenarios

[Philip Homburg <[e-mail]>]

>Unless I'm mistaken, Ole is saying that a dhcp6-pd lease for time period 
>X is a contract for time period X, during which the ISP should retain 
>enough state that if the CPE issues another dhcp request within time 
>period X, they will receive the same prefix.  However, when time period 
>X elapses, the ISP is fully within their rights to assign a different 
>prefix.

The way I understand DHCP leases is that for the duration of the lease, 
the party that obtained the lease has exclusive use of the address or prefix.
So it is a requirement on the DHCP server to avoid giving the lease to another
party.

As far as I know it never said anything about getting the same address or 
prefix if you do a DISCOVER.

A related point, and that's where it starts getting complicated, is that 
over time DHCP got used for access control. Initially DHCP was just a way
for making sure that everybody got a unique address, but you could just
use any address you liked at the risk of collision.

These days access routers restrict source addresses to whatever was offered in
a DHCP lease. And this is where it gets messy. 

In theory we could specify how access routers could do the right thing. And then
get CPEs to do the right thing as well.

But I think it would be more productive to make hosts more robust.