The 3 styles of NAT

By | July 6, 2013

Dynamic NAT

Dynamic NAT is a one to one NAT, however you setup an IP pool of NAT’d IPs so when devices cross networks it will NAT them to the pool created.  It can also work in conjunction with DNS to assist with overlapping address ranges.  This is the least common form of NAT.

NAT Overload

The most common form of NAT.  Many clients behind a router or firewall will NAT when going through the router to one main IP.  The router uses the source port to keep track of the source host.  This form of NAT is commonly called PAT (Port Address Translation).  This information gets held in a NAT Table that can be viewed on the layer 3 device.  If a source port is already being used the router/firewall will just increment the port and give the source host the next available one.

Static NAT

This is a one to one translation.  You NAT an internal address to a public address.  The same applies to the public IP, it will always NAT to the same internal address.  These IPs do not need to be assigned to an outside interface, they simply exist as NATs that get used when the router needs them.  You can also use ports with static NATs so the same public address can NAT to different internal IPs based on the port number.  This allows your email and web servers to share one public IP and traffic get routed properly based on the port it is using.