IPv4 Address Exhaustion and the Workaround Options

Without sufficient global IPv4 address space, hosts are forced to work with mechanisms that provide the capability for an internal (private) IP address space to be translated to a smaller or single externally routable IP address space. Network Address Translation (NAT) enables multiple devices to use local private addresses (RFC 1918) within an enterprise while sharing one or more global IPv4 addresses for external communications. Although NAT has to some extent delayed the exhaustion of IPv4 address space for the short term, it complicates general application bidirectional communication. These workarounds have resulted in the following:

• Establishing gateways, firewalls, and applications that require specialized code to deal with the presence of NAT/PATs (for example, NAT transparency using UDP)

• Mapping of standard ports to nonstandard ports (port forwarding)