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?
ASA
Cisco PIX/ASA Site-to-Site IPsec VPN Configuration
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.