I have a Cisco 1921 router with VPN configured on it, at the moment, Internet Modem (ISP modem) is in bridge mode. Problem happens when Public IP changes since this branch doesn't have a static IP. I have tried DDNS (DynDNS) but it didn't work, explored many forums for DDNS issue but nothing helped.. I am now thinking to use ISP modem in routing mode because DDNS works absolutely fine with this modem. My question is: where would the NAT stand, since ISP modem can also do NATTING and what other settings would I need in order to configure VPN on cisco router? Do I need to disable it on ISP modem? Will I need Port-forwarding on ISP modem?