Tunneling ipv6 over gif

["Steven M. Bellovin" <smb%bellovin.org@localhost>]

I'm trying to set up a tunnel from a NetBSD machine to a Cisco router.
The goal is to carry v6 traffic.  Ultimately, the NetBSD machine will
be a router; for the moment, though, I'm just trying to get the
point-to-point stuff working.  

Following gif(4), I've done

        ifconfig gif0 create
        ifconfig gif0 myV4addr theirV4addr up
        ifconfig gif0 tunnel inet6 myV6addr theirV6addr

Ifconfig shows that correctly, though it doesn't show anything in the
v6 routing table for the v6 addresses.

The man page says

        route add E 0

next.  That -- or, more precisely,

        route add -inet6 anything 0

fails because 0 is invalid.

I've done a bunch of other additions to get something into the routing
table, such as

        route add -inet6 default theirV6addr

followed by the suggested

        route change -inet6 default -ifp gif0

but tcpdump shows nothing going out over the Ethernet.  Instead, I see
oerror going up (via 'netstat -I gif0 N').  ping6 doesn't see any
errors, though, and an examination of the code paths in if_gif.c and
in6_gif.c doesn't show any obvious (or even plausible) cause of the
errors.

Suggestions?