In most cases, a branch office uses a static outside IP address to connects to a main office by configuring a site-to-site IPsec VPN between two Cisco ASA firewalls with static IP address on both end, But what if one of the remote ASA firewalls has a dynamic IP address?
The Site-to-Site IPsec VPNs were used to connect two distant LANs together over the Internet. Private addresses were used on the LAN that means without tunneling the two LANs would be unable to communicate with each other.
How to stretch your network behind firewall to Windows Azure and setting up a Site to Site VPN using RRAS.
You may planning to stretch your datacenter network to Windows Azure by setting up a Site to Site VPN where the VMs up in Azure are effectively connected to the Enterprise Datacenter. The Site to Site VPN just extends the datacenter to allow for VMs to be created in the cloud With VMs both on-premise and up in Azure.
You’ve probably read guidance requiring you to have two network adapters, one for internet facing traffic and the other for internal facing traffic. You may have also read that you must assign a static public IP address on the Internet facing network adapter as you cannot NAT the traffic.