NAT stands for network address translation. It's a way to map multiple local private addresses to a public one before transferring the information. Organizations that want multiple devices to employ a single IP address use NAT, as do most home routers.
NAT can be used in different scenarios, sometimes to protect portions of your network from the Internet, sometimes to save the IPv4 address space, and in smaller networks is also used to share a single Internet connection with a single routable IP allocated.
It enables private IP networks that use unregistered IP addresses to connect to the Internet. NAT operates on a router, usually connecting two networks together, and translates the private (not globally unique) addresses in the internal network into legal addresses, before packets are forwarded to another network.
NAT is a very important aspect of firewall security. It conserves the number of public addresses used within an organization, and it allows for stricter control of access to resources on both sides of the firewall.
NAT conserves the number of globally valid IP addresses a company needs and -- in combination with Classless Inter-Domain Routing (CIDR) -- has done a lot to extend the useful life of IPv4 as a result. NAT is described in general terms in IETF RFC 1631.
Network Address Translation (NAT) technology is a workaround to extend the lifetime of IPv4 addresses. NAT allows organizations to extend their addresses to more devices by using private IPv4 address space, and APNIC recognises this is an operational reality for many network operators due to IPv4 exhaustion.
By translating multiple private addresses carried in IPv4 headers into one unique public address, NAT allows multiple intranet users to access the Internet using only one public address, effectively mitigating public IPv4 address exhaustion.
Network Address Translation (NAT) converts local ip to global ip. Routing is the process to route the data packet from one network to the other.