I have an ASUS N66U
I have configured the WAN interface to use a VPN Client to connect to a 3rd party VPN Server, so that all NAT LAN connected device traffic is routed through the 3rd party VPN server.
But if the 3rd party VPN server goes down, or the connection is otherwise lost or broken, the Asus N66U will route directly from the WAN connection using e.g. my ISP.
How can I stop my Asus N66U from routing any traffic on the WAN port if the VPN connection is down?
At the very least you will need to allow it to route VPN traffic on that port, otherwise your VPN connection won’t work and/or won’t be re-established.
I want it to drop all connections if it is not on the vpn.
It can never be on the VPN if the outer, encrypted VPN packets are not allowed on the connection. I mention it because it is one of the more complex bits to handle about your requirement, depending on if you always connect to the same IP via VPN or need to connect to a dynamic peer, possibly one you need to look up via DNS first.