Network address translation

Network address translation (NAT) modifies IP address information in packet headers as traffic passes through a router or gateway, allowing multiple devices to share addresses or connecting networks that use different address spaces.

Port address translation: A form of NAT that distinguishes connections by translating transport-layer port numbers as well as IP addresses. This common form lets many private devices share one public IPv4 address.
Internet Protocol: The network-layer protocol that carries datagrams between hosts using logical addresses. NAT operates on the source and destination addresses that IP uses for forwarding.
Home router: A device that connects a home network to an external network and often provides routing, firewall, and wireless functions. Home routers commonly let many household devices share one public IPv4 address.
IPv6: The sixth version of the Internet Protocol, using 128-bit addresses. Its vast address space reduces the need to share public addresses through NAT.
Connection tracking: A firewall function that records active network flows and their state. NAT uses flow state to map returning packets to the originating internal host.
IPv4: The fourth version of the Internet Protocol, using 32-bit addresses. Its limited address space helped drive widespread address sharing through NAT.
Carrier-grade NAT: A provider-side system that shares public IPv4 addresses among customers using address and port translation. It extends address sharing beyond the customer's own gateway.
Firewall (computing): A system that controls network traffic according to security rules. Firewalls enforce access policy; address translation alone does not provide equivalent protection.
IP packet: A unit of data carried by the Internet Protocol, with a header containing source and destination addresses. NAT changes address fields in these headers while packets cross a gateway.
Private network: A network using addresses that are not globally routed across the public Internet. NAT commonly translates private addresses into globally reachable addresses.

Linked from 12 pages