What is Network Address Translation

What is Network Address Translation?

Network address translation (abbreviated as NAT), also called network masking or IP masking, is a technology that rewrites the source IP address or destination IP address of IP packets when they pass through a router or firewall. This technique is commonly used in private networks that have multiple hosts but only access the Internet through a public IP address.

NAT classification

There are three types of NAT: static NAT (StaticNAT), dynamic address NAT (PooledNAT), network address port translation NAPT (Port-LevelNAT) ).

Among them, Network Address Port Translation NAPT maps the internal address to a different port of an IP address on the external network. It can hide small and medium-sized networks behind a legitimate IP address. NAPT is different from dynamic address NAT. It maps internal connections to a separate IP address in the external network and adds a port number selected by the NAT device to the address.

NAPT is the most commonly used conversion method, and it is also mainly used in HomeGW. It also contains two conversion methods: SNAT and DNAT.

(1) Source NAT (SourceNAT, SNAT): Modify the source address of the data packet. Source NAT changes the source address of the first packet. It is always done before the packet is sent to the network. Packet masquerading is an example of SNAT.

(2) Destination NAT (DestinationNAT, DNAT): Modify the destination address of the data packet. DestinationNAT is just the opposite of SNAT. It changes the destination address of the first data, such as load balancing, port forwarding and transparent proxy, which belong to DNAT.

NAT usage examples

1. Load balancing: Destination address translation NAT can redirect connections from some servers to other randomly selected servers.

2. Failure termination: Destination address translation NAT can be used to provide high reliability services. If a system has a critical server accessed through a router, if the router detects that the server is down, it can use Destination Address Translation (NAT) to transparently transfer the connection to a backup server.

3. Transparent proxy: NAT can redirect HTTP connections to the Internet to a designated HTTP proxy server to cache data and filter requests. Some Internet service providers use this technique to reduce bandwidth usage without having their customers configure their browsers to support proxy connections.

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