With a vanilla 4.5.0.19 install i also use an openvpn vpn (see my related Feature Request Make IPv6 payload work in openvpn).
My network provider (KPN in The Netherlands) has recently changed to IPv6 only with CLAT i need a few workarounds before i’m able to use my VPN:
- When setting up the VPN usually a host route is created for the IP address of the host on the other side of the tunnel. This fails, probably because the default gateway has a device but no gateway address. Because the default gateway is moved to the VPN the VPN tries to route it’s traffic into itself which obviously doesn’t work. My workaround is to create this route myself before starting the VPN
- Because openvpn somehow doesn’t use the IPv6 configuration pushed to it, the default gateway for IPv6 keeps routing to the mobile data connection. My workaround is to remove this default gateway.
- Because the CLAT traffic is actually just IPv6 traffic where IPv4 addresses are embedded inside IPv6 prefixes just removing the IPv6 default gateway breaks the tunnel connectivity. My workaround is to add a route for 64::/16 to the gateway that was used by the default gateway.
With these workarounds in place my VPN works as expected.