My VPN over dial backup is not working when my Cable/DSL fails. I pull out the WAN link and verify the connection status, it states I have an M-Estab. VPN session on the Device Status page. When the WAN link is up I see Q-Estab. under VPN Status.
You need to configure the VPN router at the host site with two VPN connections, one for the Wan Ethernet and one for the Async Network Interface. Also, on your client RF550VPN, when creating the VPN connection, the network interface should be set to AUTO.