Hi Yves,

similar to what's stated on https://wiki.strongswan.org/issues/1008
I've had to add this:
-(snip)-
# cat /etc/strongswan.d/proxyndp.updown
case $PLUTO_VERB in
        OUTDEV=$(ip -6 r get ${PLUTO_PEER_CLIENT%????}|sed -ne 's,^.*dev \(\S\+\) .*,\1,p')
        up-client-v6)
        ip -6 neigh add proxy ${PLUTO_PEER_CLIENT%????} dev ${OUTDEV:-eth0}
        ;;
        down-client-v6)
        ip -6 neigh delete proxy ${PLUTO_PEER_CLIENT%????} dev ${OUTDEV:-eth0}
        ;;
esac
#
-(snip)-
to make my IPv6 work correctly inside my tunnels. I've enhanced the named
script from the bug slightly so that also allow for more than just an eth0
interface.

It would be nice if the Debian package could ship that by default until
upstream has included this or an equivalent fix to the issue.

Cheers,
Kilian