Network Security, Firewalls, and VPNs, 3rd Edition

Using VPNs with Network Address Translation (NAT)

VPNs and network address translation (NAT) have historically suffered from some conflicts when used together. NAT is an Internet standard that allows you to use one set of IP addresses on your internal LAN and a second set of IP addresses for the Internet connection. A device (usually a router or firewall) stands between the two connections and provides NAT services, managing the translation of internal addresses to external addresses. This allows companies to use large numbers of unregistered internal addresses while needing only a fraction of that number of addresses on the Internet, thus conserving the addresses. This is similar to a company that may have hundreds of phones in a building ...