Network Address Translation (NAT)

Process of mapping or translating one IP address to a different IP address (or addresses) by modifying the network address information in the IP header of the network packets.

This method is used to map a single public (routable) IP address to one or more private (unroutable) IP addresses. This helps prevent the exhaustion of public IPv4 addresses.

Static NAT

  • NAT device is assigned a pool of public IP addresses
  • Private IP addresses are mapped to the public IP addresses
  • Used in situations that require servers to always be mapped to the same public IP address

Dynamic NAT

  • NAT device is assigned a pool of public IP addresses
  • Public IP addresses are used when they are needed by a host and then returned to the pool once they are no longer in use
  • Used in situations in which the public IP address does not need to be consistently mapped to the same private IP address

Port Address Translation

  • A single public IP is assigned to a network
  • All the devices on the network share a single IP address
  • The NAT device records the private IP address as well as the port - also called the source port address - used by the internal host to ensure that communication is sent back correctly
  • This is the most common type of NAT
  • Helps conserve the number of available IP addresses

Source NAT (SNAT)

  • Preserves the destination address and modifies the source address
  • Allows hosts on a private network to initiate a connection to hosts outside of the private network

Destination NAT (DNAT)

  • Preserves the source address and modifies the destination address
  • Allows a host (or multiple hosts) outside of the private network to connect to a host inside a private network