I plan to set up VPN connections through dial-up as a backup. This is meant to be between an RF660 and an RF550. Only the RF550 will be incorporated with a backup link. I don't want to increase the number of IPSec connections. How can I do this?

You only need to create one connection.

You must use FQDN and DDNS when you setup your VPN tunnel.

On the RF550VPN, you must use DDNS. When you configure the VPN tunnel, you need to set the interface to Auto.

On the RF660VPN, you must configure the VPN using FQDN based on a DDNS name.