> NetBSD/i386 based.
>
> My experience in tunnels is limited to ipv6/gif tunnels

my experience of ipv6/gif tunnels is (while it's short experience) that
they Just Works (TM) :)

i just read man, asked few questions on netbsd-users, did what i wanted
and it works.

> What kind of tunnel is better for this case?
>

gif. remember you can tunnel ipv4 over ipv4 too.

with ipv4 only use vtun - similar functionality but with excryption and
compression.

unfortunately NetBSD tun device doesn't work with IPv6, so vtun does not
too.