IPv6-over-IPv4: "RTNETLINK answers: No route to host"-Error

Hello,

I'm trying to setup a 6to4-tunnel provided by sixxs.net on my
gentoo-Linux-box (Kernel 2.6.8.1)
When I follow the instructions found here:

http://forums.gentoo.org/viewtopic.php?p=1449382

I get the following error:

# ip tunnel add sixxs mode sit local 132.187.247.3 remote 212.224.0.188
# ip link set sixxs up
# ip link set mtu 1280 dev sixxs
# ip tunnel change sixxs ttl 64
# ip -6 addr add 2001:6f8:900:ff::2 dev sixxs
# ip -6 ro add default via 2001:6f8:900:ff::1 dev sixxs
RTNETLINK answers: No route to host

I checked every possible thing, but something still must be wrong. I can set
up a tunnel when I boot into winXP, so protocol 41 is routed.

Anyone any idea?

Greets
Thorsten