rtadvd/rtsold failing to assign a v6 address

[Johan Ihren <johani%johani.org@localhost>]

This is with NetBSD around 5.0.1, although I don't think that matters.

I haven't used address autoconfiguration for quite a long time, but now I have 
an application where I absolutely need this. The way it used to work was 
basically that I ran "rtadvd {interface}" on the upstream router and "rtsold 
{interface}" on the downstream client and everything would work out, i.e. the 
client would assign an address from the prefix supplied by the router, add 
suitable prefixes to its routing table (typically a default route) and 
everything would be fine.

Now I see the following:

client has in rc.conf:

ip6mode=autohost
rtsold=YES
rtsold_flags="vlan1"

router has in rc.conf:

ip6mode=router
rtadvd=YES
rtadvd_flags="vlan1"

There is (currently) no rtadvd.conf, but that shouldn't be necessary.

Watching the traffic on the wire I see the router solicitation go out, I see 
the router advertisment arrive at the client. I also see that it contains the 
correct local prefix. But no address assignment is done. 

I have several other boxes (or rather Xen VMs) configured as "ip6mode=autohost" 
in the same way. They assign v6 addresses just fine. The only difference that I 
can see is that in that case the upstream router is a Cisco... This would seem 
to suggest that the problem is in the router end. But I fail to see what it is, 
as the RA arrives nicely at the client, with the correct (AFAIK) contents.

What am I doing wrong?

Regards,

Johan Ihrén