NAT Technology and Proxy Server

Network Address translation NAT:

Our host in the private network has been assigned to the local IP address, we now want to communicate with the host on the Internet, what can we do?

The simplest way is to try to apply for some global IP addresses. But this is not easy, because the global IPv4 address is not much left. Currently the most used method is to use network address translation.

Network address translation requires the installation of NAT software on a router with a private network connected to the Internet. The router that installs the NAT software is called the NAT router, and it has at least one valid external global IP address. This allows all hosts using local addresses to communicate with the outside world by translating their local addresses into global IP addresses at the NAT router to be able to link to the Internet.

Let's look at an example:

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The NAT router receives an IP datagram from host a from inside the private network to Host B on the Internet: the source IP address is 192.168.0.3, and the destination IP address is 213.18.2.4. The NAT router converts the IP datagram's source IP address 192.168.0.3 to a new IP address (that is, the NAT router's global IP address) 172.38.1.5, and forwards it. Therefore, Host B receives the datagram, assuming that the IP address of a is 172.38.1.5. When B sends an answer to a, the destination IP address of the IP datagram is the IP address of the NAT router 172.38.1.5. B does not know the private address of a 192.168.0.3. In fact, even if you know it, you cannot use it because routers on the Internet do not forward IP datagrams with destination addresses that are private network local IP addresses. When the NAT router router receives the IP datagram from Host B on the internet, it also has to convert the IP address once. With the NAT address translation table, the old destination IP address 172.38.1.5 on the IP datagram can be converted to the new destination IP address 192.168.0.3 (host a true local IP address).

Proxy Server:

The proxy server function is the proxy network user to obtain the network information. The image says, it is the intermediary of the network information. In general, when we use a Web browser to link to other Internet sites directly to obtain information, we need to send out a request signal to get the answer, and then the other party to the information sent back in bit mode.

The proxy server is a server between the browser and the Web server, and with it, the browser is not directly to the Web server to retrieve the Web page but to make a request to the proxy server, the request signal will be sent to the proxy server first, The information needed by the proxy server to retrieve the browser and send it to your browser. Moreover, most proxy servers have buffering capabilities, like a large cache, which has a lot of storage space, and it constantly stores the newly acquired data on its native memory, if the browser is forcing the data to be present on its native test memory and is up-to-date, Then he does not re-fetch the data from the Web server and directly transmits the data on the memory to the user's browser, which can significantly improve the speed and efficiency of the browser.

NAT Technology and Proxy Server