6.0-RC1 IPv6 losing local subnet route

[Craig Boston]

On Sat, Oct 29, 2005 at 12:04:53AM +0900, SUZUKI Shinsuke wrote:
> I tried the same test using my PC with fxp drivers, but your phenomena
> did not happen in my environment (at least for five hours).
> 
> Maybe the configured prefix was regarded as off-link by some reason.
> (it is theoretically possible in IPv6, but I'm not sure whether it
> really happens in your case)

I don't think this is the case, ndp looks normal:

2002:abcd:ef01:5555::/64 if=em1
flags=LO vltime=infinity, pltime=infinity, expire=Never, ref=0
  No advertising router
[ followed by a whole bunch of link local addresses from all my vlans on
a different interface ]

However, I think I've isolated the trigger.  I noticed that on bootup,
the route was _always_ missing.  There was also duplicate ifconfig
output -- once from rc.d/netif and once from devd upon getting "link
up".

Knowing that, I can cause it to happen on command by manually
re-configuring an interface with an address it already has:

With em1 up but not configured yet:

# ifconfig em1 inet6 2002:abcd:ef01:5555::20
(routes are all normal)

# ifconfig em1 inet6 2002:abcd:ef01:5555::20
(prefix route disappears)

It's also been a lot more stable today than yesterday.  However
yesterday I was moving some cables around so there were lots of link
down / up events.  My guess is that devd was dutifully reconfiguring the
interface on link up and causing the random drops.

There is a slight delay between the second ifconfig and the route
disappearing -- less than 0.5s.  During that window I managed to capture
the following seemingly inconsistent output fron ndp -p:

2002:abcd:ef01:5555::/64 if=em1
flags=LO vltime=infinity, pltime=infinity, expired, ref=0
  No advertising router

-- Craig