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

[Nick Hilliard <[e-mail]>]

Christian Huitema wrote on 05/02/2019 22:10:
> Lots of the discussion centers on denial. "Don't worry about that, the
> router's prefix should not change." Really?

We know the router's prefix will change.  The challenge is transferring 
the state information from one domain to another, so that when it 
changes, the end devices can recover as quickly as possible.

Mark is spot on to note that TCP and UDP require addressing stability. 
Changing from TCP and UDP is boiling the ocean, which means that if we 
want to deal with this problem, we need to work with what we have.

The choices seem to be:

1) ensuring that if a device is disconnected and then reconnects to the 
same network, the device will be given the same lease,

2) the intermediate device remembers the old lease, compares it with the 
new lease and if they're different, invalidates the old prefix by 
issuing an updated PIO,

3) pushing the smarts down to the host layer and detecting / monitoring 
whether any particular prefix is still valid

4) ???

Fernando's suggestion is workable but requires CPE vendors to get on 
board with the idea of storage of addressing information.  Getting ISPs 
to change DHCPv6 assignment policies is also workable, but requires 
centralised provisioning and dynamic routing.

None of these is ideal and all of them require compromise and some 
change in behaviour in a way that has side effects.

This is because the core problem is about how to deal with transfer of 
state information.  Managing state is always a monumental headache.

Nick