UCSD tunnel behing NAT and Firewall setting ?

Hi there I know that VPN can be done behind firewall NAT (from the client side) Can the IPIP be made (from the gateway side) behind a Firewall (that allow any traffic outbound) and a NAT ? Untill few month ago my gateway sited on the DMZ and it worked But i had changed the DMZ to point another IP and it seems that the IPIP still work .. I wonder if it is a router problem or the IPIP can pass thru like a VPN can pass Thanks For any Info ronen- 4Z4ZQ http://www.ronen.org Ronen Pinchooks (4Z4ZQ) WebSite<http://www.ronen.org/> ronen.org (Ronen Pinchooks (4Z4ZQ) WebSite) is hosted by domainavenue.com www.ronen.org