By the early-to-mid 1990s, network architects and engineers began to realize that the number of potential addresses provided by the IPv4 standard would not last nearly as long as was once thought. In May 1994, RFC 1631, The IP Network Address Translator (NAT), was released by authors Kjeld Borch Egevang and Paul Francis. This Request for Comment (RFC) introduced a mechanism that allowed for the reuse of private IP addresses, defined in RFC 1918, to combat the rapidly disappearing public IP address space. 

Today, we take NAT for granted, but when this RFC was released in 1994, it was a considerable revelation. Even though RFC 1631 acknowledges that the authors were not the first to conceive the idea of using private addressing space that anyone could use and then simply translate it into real-world routable addressing, it was a thought that very few people had the foresight to envision at the time. 

While many network administrators and engineers may have first learned to configure network address translation via NAT and the newer version PAT (Port Address Translation) on routers, it is predominantly a firewall function. As such, we will see in this whitepaper the real power of the Cisco ASA and its ability to combine variations of NAT and PAT in advanced configurations. 

Continue reading to learn more about Cisco ASA NAT and PAT.