Teste VPN Konfiguration
openvpn --config /etc/openvpn/tun0.conf --verb 6
First you need to enable proxy_ndp:
sysctl -w net.ipv6.conf.all.proxy_ndp=1 (and add the corresponding line un /etc/sysctl.conf).
The the correct commands are:
ip neigh add proxy 2a00:d880:6:f2:80::1000 dev eth0 ip neigh add proxy 2a00:d880:6:f2:80::1001 dev eth0
assuming that eth0 is the name of your non-OpenVPN network device. This means that this host should serve a a NDP proxy on devcie eth0: it should say "yes it's me" when someone is asking for "2a00:d880:6:f2:80::1000" on the dev0 link; this mean that this host will receive the packets for 2a00:d880:6:f2:80::1000 coming from the eth0 link; you do not need to tell him on which interface is the real 2a00:d880:6:f2:80::1000, the IPv6 routing table will take care to route the correct to the suitable destination. And do not forget to enable IPv6 IP forwarding:
sysctl -w net.ipv6.conf.all.forwarding=1