NAT Configuration Primer

One of the things we'll remember about 2015 is that it was the year ARIN finally ran out of public IPv4 space. Yet despite the depletion, IPv4 is still the dominant addressing mechanism running on the vast majority of organizations today. And in many cases, few are in any big hurry to migrate over to IPv6. The reason that most IT professionals ignored the doomsday cries regarding IPv4 exhaustion is that many companies relied on Network Address Translation (NAT) to significantly reduce the number of public IP addresses they required.

In fact, these days, it's not uncommon for small companies to operate with a single public IPv4 address. And if your company is larger and requires connectivity/redundancy using external BGP peering, then an IPv4 subnet that has 254 usable addresses will work just fine. This provides 254 publically addressable IP addresses -- plenty of addresses to operate a decent sized, publically accessible data center and thousands of employees. NAT is the key to limiting the need to have public addresses assigned to all internal devices in a 1-to-1 ratio.

In this guide, we'll explain how NAT works and walk you through the two NAT configuration options: static NAT translation and Port Address Translation.

(Image: TonisPan/iStockphoto with modification)