> 	(1) # ifconfig p2p0 inet6 A B prefixlen 64 alias
> 	(2) # ifconfig p2p0 inet6 A B prefixlen 128 alias
> 	(3) # ifconfig p2p0 inet6 A prefixlen 64

> 	with the lastet KAME, (1) is illegal and rejected.  (2) and (3) works
> 	happily.  maybe we should ignore netmask on (1) configuration and treat
> 	it as (2).  don't remember why we did not do so.

IIRC, the point we (KAME) discussed in KAME meeting is that:
	(1) is obviously didn't work well at that time.
	(1) is not correct in terms of prefixlen.
	Ignoring prefixlen for (1) is confusing with (3).
		If prefixlen to be ignored, it should not be printed in
		ifconfig output.
		The kernel code should be 'hacked'
	How to do if 'prefixlen 64' is explicitly specified?

Atsushi Onoe, KAME