[c-nsp] Backup Interface & IPv6 - why is Cisco sleeping?

[Garry]

<rant>
Having just installed a set of nice ASR1k boxes with rather new IOS, I
noticed Cisco has still (after many years and many IOS releases) not
managed to get Backup Interfaces & IPv6 to work with each other ... or
I'm missing something ... but while IPv4 addresses on backup interfaces
work just fine, IPv6 config will lead to the backup interface to no come
up due to the IP address overlapping with the IP address of the primary
interface (what a surprise - it's the BACKUP INTERFACE, for crying out
loud ...)

With Cisco presenting themselves and their hardware oh so v6-ready
(which they are for most parts I guess - all other features at least we
require for production use seem perfectly fine), I'm really starting to
wonder whether we're the only ones on this earth still using a dual
switch config for our routers for redundancy purposes ...
</rant>

-garry