Re: Addressing plan exercise for our IPv6 course

[Matthew Kaufman <matthew () matthew at>]

Owen DeLong wrote:
> Why on earth would you do that? Why not just put the provider-assigned
> addresses on the interfaces along side the ULA addresses? Using ULA
> in that manner is horribly kludgy and utterly unnecessary.
>   
Because, although one of the original goals of IPv6 was for hosts to be 
easily multihomed at multiple addresses like this, host software (and 
even some of the required specifications) isn't really isn't there yet, 
and often the wrong thing happens.

Never mind that the timescale for IPv6 deployment, no matter how long it 
is, will be shorter than the timescale for updating PCI, HIPPA, and SOX 
audit checklists to remove the requirements around "hide internal 
topology" and "do not use public addresses on any interface of critical 
hosts".
> Why is that easier/cheaper than changing your RAs to the new provider and
> letting the old provider addresses time out?
>   
This would *also* require multihoming to actually work properly, only 
worse as the rules for selecting ULA vs PA routes are usually more right 
than the rules for selecting one PA vs another PA as an outbound 
interface, even if your host does multiple default routes properly. Even 
if all your hosts end up with external connectivity that works, the odds 
that they can reliably talk to each other is low.

Matthew Kaufman