Policy Routing Using Linux®

Standard NAT Defined

The traditional definition of NAT is contained in the very term itself. Network Address Translation is the act of changing an address from one to another within the packet. While this change is usually of the source address, there is no restriction. This address changing function is essentially a router function when you consider the mechanisms. Any router, due to its very nature as an intermediary between networks, may perform the NAT function.

The early history of IPv4 networking did not need to consider this type of routing function very often. Occasionally the subject would come up, but those discussions usually were centered within fairly convoluted reasoning. The IPv4 address space does contain over 4 billion addresses ...