Linux Small knowledge translation-port and port number

This time, say "ports" and "Port numbers".

Usually hear people say "open port 80th", in order to secure "do not open redundant ports" and so on. So, what are the ports or port numbers here?

First, the "port" is a concept used on TCP or UDP and is often likened to "windows". Also, the port number is likened to the window number.

For example, when sending money to the post Office, not every window can be remitted, only a specific window can handle the remittance business. Therefore, each window will be numbered.

The port number is similar to the above, for example, when the Web server accepts traffic over HTTP, it communicates through port 80th of the Web server.

Similarly, Smpt uses port 25th to communicate, and SSH uses port 22nd to communicate. So the port as a "window of communication" to consider also good.

In addition, the client communicates with the port. However, the port number on the server is basically fixed, and the client's ports are basically changed every time they communicate.

Although the port number of the server is fixed, in fact, as long as the configuration, you can also use other port number to communicate. However, "Some servers use port 25th to accept HTTP requests, and some servers use port 80th to accept HTTP requests",

Then each server uses the port number will appear very messy, without regularity, will naturally bring chaos. As a result, the port number on the server is set to a certain extent. These specified port numbers are referred to as "well known ports".

Almost all servers use "well known ports" to communicate. The previously mentioned "SSH service uses port 22nd, port 80th for HTTP Service" is well known ports.

Well known ports  0-1023registered ports  1024x768-49151  Dynamicand49152-65535

Well known ports is managed by "internet Assigned Numbers Authority (IANA)" this organization. The IANA organization, in addition to managing the well known ports, is also focused on standardizing IP addresses and domain names.