v6 vs gif

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

The machine at work that was routing v6 developed a bad spot on its
disk.  As a matter of convenience (what I had on a disk at ready hand),
I tried to set up 4.0 to do the same job.

But it doesn't work.  It involves a gif v6-in-v4 tunnel.  I had to add
a "create" (the former OS was pre-cloners), but then the next thing I
ran into was:

# ifconfig gif0 create
-> works fine

# ifconfig gif0 tunnel (our v4 address) (our peer's v4 address)
-> works fine

# ifconfig gif0 inet6 (our v6 address) (our peer's v6 address)
ifconfig: SIOCAIFADDR: Invalid argument

I had a look at gif(4) and didn't see any reason to think this
shouldn't work.  Explicitly including "ifconfig gif0 up" before the
attempt to set the v6 addresses doesn't help; the only apparent
difference it makes is that gif0 acquires a link-local v6 address.
"route -n flush -inet6" doesn't help either.

My first suspicion was that the kernel didn't have v6 support, but
every up interface has a link-local v6 address, which kills that theory.

Is this pilot error of some sort, something I should be doing
differently under 4.0?  Or is gif busted?  Or what?  (I can give full
details, but would rather not include real addresses on an archived
list.)

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