Network Translator

Network Address and Port Address Translator

NAT

Network Address Translator

• Mapping one set of IP addresses (usually private) to another set of IP addresses (usually public).
• Used for
  • Reuse IP address: Share a small pool of IP addresses with a large number of hosts
  • Security: internal network is invisible to the outside

PAT

Port Address Translator

• Translate transport identifiers
  • TCP and UDP port numbers, ICMP query identifiers

Example

Here is an example that shows how NAT and PAT works: