Network security rookie learning information basics

Preface: The Basics chapter contains explanations of some common terms and some basic principles of network security.
1. Domain name: domain name (English: Domain Name), also known as network domain, is the name of a computer or computer group on the Internet composed of a series of names separated by dots, used to locate the computer during data transmission Logo (sometimes also referred to as geographic location). (Explanation from Baidu Encyclopedia)
In fact, the domain name can be understood as a simple name. Under normal circumstances, when I visit a website, I need to pass the public IP of the website (what is the public IP will be mentioned later), but because the IP is too difficult to remember, so people thought of giving it an alias, so it appeared Up the domain name. Since the domain name is for the entire network, the domain name cannot be taken casually like a name, and it needs to be specified by a special organization. For example, if you own the domain name, then others cannot use it (of course, the domain name must be charged, usually for rent, of course, you may not have seen it before buying it). After you rent the domain name, you need to bind it with the server. That is, after entering the domain name later, it will automatically access the public IP you bound.
2. IP: IP is the abbreviation of Internet Protocol (Internet Protocol), which is the network layer protocol in the TCP/IP system. The purpose of designing IP is to improve the scalability of the network: one is to solve the Internet problem and realize the interconnection and intercommunication of large-scale and heterogeneous networks; the other is to divide the coupling relationship between the top-level network application and the bottom-level network technology to facilitate the two Independent development. According to the end-to-end design principle, IP only provides a connectionless, unreliable, best-effort datagram transmission service for the host. (Explanation from Baidu Encyclopedia, just look at it. This explanation is not the point)
IP is divided into public IP and intranet IP (LAN IP). The public IP is your IP on the entire network, and the internal IP refers to the local area network. This thing is more complicated to explain. Remember that the public network is external and the internal network is internal. You will understand it later. Here I found an article, you can learn about it through https://blog.csdn.net/roshy/article/details/91986023
3. DNS: The Domain Name System (Service) Protocol (DNS) is a distributed network directory service, which is mainly used for the mutual conversion of domain names and IP addresses, and to control the sending of e-mails on the Internet. (Explanation from Baidu Encyclopedia)
As for the purpose of DNS, please refer to the figure below.


As shown in the figure, Ping Baidu through DNS in different places, the resolved servers are different.