Answer 

If the VPN dial-out end has a dynamic IP and dial-in end has a static IP, then you can build the LAN-to-LAN VPN normally and no special settings are required.

If the VPN dial-out end has a static IP and dial-in end has a dynamic IP, you need set up a DDNS (Dynamic DNS) account for the dial-in end, then the VPN dial-out end can build a LAN-to-LAN VPN by using the DDNS name.

Note: Vigor routers support DDNS. Once you have registered with a DDNS providers then go to “Applications>>Dynamic DNS Setup” to configure it in Vigor router.

A couple of DDNS providers are: www.dyndns.com & www.changeip.com but there are many more available.