What is Network Address Translation?

In a calculator network, Network Address Translation (abbreviated as NAT), also known as network masking or IP masquerading, is a method of rewriting the source IP address or destination when an IP packet passes through a router or firewall. IP address technology. This technique is commonly used in private networks that have multiple hosts but access the Internet through only one public IP address. It is a convenient and widely used technology. Of course, NAT also complicates communication between hosts, leading to a reduction in communication efficiency.

The English full name of NAT is "NetworkAddressTranslation", which means "Network Address Translation" in Chinese. It is an IETF (Internet Engineering TaskForce, Internet Engineering Task Force) standard that allows an entire organization to appear on the Internet with a public IP (Internet Protocol) address. As the name suggests, it is a technology that translates internal private network addresses (IP addresses) into legitimate network IP addresses.
No NAT network, assuming that each access subnet requires a set of / 24 IPs, and can also be connected externally, at least external routes must be reserved or applied for 1000 external IP networks with NAT, and access to the subnet through NAT translation Private IP can be used. When connecting externally, the relationship between private IP and external IP is bound by routing. Modify the address on the transmitted IP packet, so only 255 external IPs can be used to meet the external connection needs of the internal access subnet
In the mid-1990s, NAT became popular as a solution to the shortage of IPv4 addresses to avoid the difficulty of retaining IP addresses. Network address translation is widely used in many countries. Therefore, NAT has become a standard feature of routers on home and small office network connections, because for them, the cost of applying for an independent IP address is higher than the benefits.
In a typical configuration, a local network uses a designated subnet of a private network (such as 192.168.xx or 10.xxx) and a router connected to this network. This router occupies a private address in the network address space (such as 192.168.0.1), and it also passes one or more
There are three types of NAT: Static NAT (StaticNAT), Dynamic Address NAT (PooledNAT), and Network Address Port Translation NAPT (Port-LevelNAT).
Among them, Network Address Port Translation NAPT (NetworkAddressPort Translation) maps internal addresses to different ports of an IP address of an external network. It can hide small and medium networks behind a legitimate IP address. NAPT is different from dynamic address NAT. It maps internal connections to a single 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 will always be completed before the packet is sent to the network. Packet spoofing is an example of SNAT.
(2) DestinationNAT (DNAT): Modify the destination address of the data packet. DestinationNAT is just the opposite of SNAT. It is the first destination address that changes data. For example, load balancing, port forwarding, and transparent proxying belong to DNAT.
The host under a NAT-capable router does not create a real IP address and cannot participate in some
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