ping (network diagnostic tool):
Ping is a command under Windows, Unix and Linux systems. Ping also belongs to a communication protocol and is part of the TCP/IP protocol. Use the "ping" command to check whether the network is connected, which can help us analyze and determine network failures .
The principle is this: use the uniqueness of the IP address of the machine on the network to send a data packet to the target IP address , and then ask the other party to return a data packet of the same size to determine whether the two network machines are connected and what is the delay .
Ping is to test the network by sending a test packet to a website to see if the other website responds and count the response time. ping, the network is connected.
Intranet, extranet, routing:
The number of external network IPs is limited, and the internal network IPs are allocated through routing.
Extranet (Internet)
intranet. Please take a look at the picture below: In fact, many times our computers are not directly connected to the Internet (external network). In the figure below, you can see that there is a router (layer 1), a switch (layer 2), and then your own computer.
The intranet starts from below the router, and the IPs are all IPs starting with 192. It can be seen from the picture that the computer is connected to the external network only after the switch and the router. Why has to be this way? In fact, the external network IP is relatively tense, and the popularity of the current computer makes the external network IP not enough at all. The generation of the intranet is to solve this problem!
Extranet. A network that can access the Internet without a router or switch can be directly accessed by the outside world. No need to go through any equipment, directly connect to the computer.
Ordinary people can't have an external IP, because it is too wasteful for a person to use an external IP. So we all go to the Internet through the intranet. The external network IP is generally used for companies, schools and other institutions. What are the external IPs? In fact, the IP other than the internal network IP is the external network IP. It's that simple.
The difference between a router and a cat:
Cat: Modem, through which the computer can dial up the Internet.
Router: The role of the router is to enable several computers to access the Internet at the same time with one network cable, which plays a role in distribution. The top is connected to the cat, and the bottom is connected to the computer.
The ports are different:
(1) 4 ports are the most common wireless routers, and there are obvious antennas as identification signs;
(2) There are two ports for cats: one is connected to the telephone line, the other is connected to the RJ-45 port (network cable);
The connection is different:
(1) The cat is connected to the telephone line and (router or computer);
(2) The router connects the cat and the computer through wired or wifi
Distinguish switches, routers, and cats:
The cat, equivalent to translation, translates a data protocol into another data protocol; the function is to convert the signal of the telephone line into a digital signal, transmit it to the computer, and then convert the digital signal of the computer into a telephone signal and transmit it, thereby The realization of the computer through it and the telephone line to the Internet.
Routers generally have one port: RJ-45, but one is connected to the external network and the other is connected to the local area network; it is a network device. It can enable multiple computers connected to it to access the Internet at the same time (100M bandwidth, the sum of multiple computers reaches 100M, which will affect each other).
Switch: is a network device. It can make multiple computers connected to it form a local area network, and if there is a proxy server, it can also realize the function of surfing the Internet at the same time. It does not have the router's function of automatically identifying the sending and arriving addresses of data packets, but it has a higher transmission speed than the HUB, because it can transmit data packets to all computers connected to it at the same time, and all computers share its bandwidth rate. That is, the bandwidth of 100M, no matter how many computers are connected, the bandwidth of each computer reaches 100M in theory.
https://jingyan.baidu.com/article/046a7b3e15eb73f9c37fa96f.html
DNS：
DNS (Domain Name System, Domain Name System), a distributed database on the Internet that maps domain names and IP addresses to each other , enables users to access the Internet more conveniently without having to remember IP strings that can be directly read by machines. The process of obtaining the IP address corresponding to the host name through the host name is called domain name resolution (or host name resolution).
Each IP address can have a hostname consisting of one or more strings separated by decimal points. With a hostname, instead of memorizing the IP address of each IP device, just remember a relatively intuitive and meaningful hostname. This is what the DNS protocol is supposed to accomplish.
Telephone line->cat->network cable->router->network cable->switch->computer