History of Internen:
ARPAnet (US military command network) - > TCP / IP (1970s) (packet switching technology in 1980s) (web technology in 1990s) (these three technologies are the three technologies that are the key symbols of the mature core of the Internet) - > ansnet - > Internet

Typical Internet services:

1,www(World Wide	Web)		web	Port: 80 (the channel through which network services or network programs transmit data) IP Determine the server accessed, and determine the service through the port)
	URL: Unified resource positioning
	URL Format:	agreement://Domain name or IP: port number / Web page path / Web page name
				http://www.163.com:80/123/234/345/index.html
2,FTP		File transfer protocol	Ports: 20, 21 (one for transmitting data commands and one for transmitting data files)
	
3,Email		E-mail
		agreement:	SMTP: 	Simple Mail Transfer Protocol	Port: 25 (sending)	
				POP3: 	Post office protocol generation 3		Port: 110 (receiving)
				IMAP: 	Interactive Mail Access Protocol	Port: 143 (receiving)	(You can insert pictures and multimedia information, pop3 (no)

Mailbox client:

Web client
 Advantages: simple and convenient
 Disadvantages: there is no real-time reminder of new mail, and the mail is saved on the other party's server

Client mailbox:( outlook，Foxmail)
Advantages: there are real-time reminders of new emails, and emails can be saved locally and on the server
 Disadvantages: it needs to be configured (manual configuration, arbitrary name, Chinese); pop3 Address and SMTP Address (go to the help of the official website)

Mobile email
 Advantages: carry with you
 Disadvantages: configuration required

printer:

The printer is connected to the network
 LCD screen - through the built-in system - setting IP that will do
 No LCD screen - with the help of connecting the computer - setting IP

Computer connection printer
 Start - devices and printers - add printers - add network printers - stop searching - the printer I need is not in the list - use TCP/IP Add printer to address or host name - fill in the printer just set IP(Pay attention to use WIFI If so, the computer and printer need to be in the same state, and the network is in 5 G Or both.4G)

Main Internet access methods:

Dial up networking
 advantage:
	Can I surf the Internet
	Use the telephone line to access the Internet (without rewiring)
Disadvantages:
	You can't call while surfing the Internet
 The transmission is voice signal rather than digital signal, which needs modulation and demodulation (the voice signal sent out is converted into digital signal through modem, and then converted into voice signal through modem when it reaches the place) (analog network)
Expensive:	4(Telephone (money)+4(Net money) = 8/hour
 Slow:	56Kbps = 7KB/s

ADSL(Asymmetric digital subscriber loop (a kind of dedicated line): ATM: Asynchronous transmission network)
advantage:
	The network speed is relatively fast (with protocol, generation 1 protocol: 8) Mbps，2 Proxy agreement: 24 Mbps)
	Using telephone line (no wiring), voice and digital signals are separated, and you can make calls while surfing the Internet
	The price is relatively reasonable (with monthly service)
Disadvantages:
	Use the telephone line, and the upper limit of network speed is low
	dynamic IP The address can only be used as a client to access the Internet, not as a server( IPv4 Have 2^32 An address, IPv6 Have 2^128 (address) (who accesses the Internet to whom) IP，There's no way to save now IP Yes, it's all monthly and annual, and it's not necessary to connect it)

FTTH(Optical fiber (home)
advantage:
	The upper limit of optical fiber is high (the thinner the optical fiber is, the faster the network speed is. There are single-mode optical fiber, multi-film optical fiber, and multi-mode core optical fiber can transmit multiple optical fiber signals) (the optical fiber is afraid of folding and cannot exceed 90)°，Broken (for welding)
Long transmission distance and high speed
 Price and ADSL agreement
 Disadvantages:
	dynamic IP address
	Rewiring of optical fiber (insufficient network speed) WIFI Agreement restrictions, can buy support WIFI6 Computers and routers (or wired)

fixed IP Optical fiber access
 advantage:
	fixed IP Address, you can build a server
 Disadvantages:
	expensive	4IP + 10Mbps = 2000~3000/month
		256IP + 200Mbps = 40 ten thousand/Year

Network protocols and standards (equivalent to defined standards and rules)
ISO (International Organization for Standardization) (WAN standard)
IEEE (American Society of electrical and Electronics Engineers)

Standard:
IEEE802.3 (wired network standard)
IEEE802.11 (wireless network standard)

Twisted pair:
(the line sequence of T568B and T568A is 1, 3; 2 and 6 are exchanged with each other) (the maximum length is 100m. If you want to extend it, you can add a switch in the middle, which has the function of restoring signal)

T568B:  
White orange	orange	White green	blue	White blue	green	White brown	Brown (line sequence)

T568A: 
White green	green	White orange	blue	White blue	orange	White brown	Brown

Through line: used to connect different network devices (Computer - switching) (Switching - routing)
	568B-568B

Cross line: it is used to connect the same kind of network equipment (computer computer) (routing) (computer routing. The enemy of the enemy is a friend. The computer uses a straight line for switching, and the switching also uses a straight line for routing, so it is considered that the computer and the router are one kind of equipment)
	568B-568A

Switch to switch:
Both through line and cross line can be used, because the switch has the function of wired sequence conversion, but generally through line is used

Full reverse line:
(it is connected to the console port and the management port of intelligent routing and switch. Only intelligent switch and intelligent router have this port, which is used for local connection management of intelligent routing and switch: reinstall the system and crack the password)

It cannot be recognized by the network card and cannot be extended. It is regarded as a local connection
 There are special console The line is flat and one end is flat console Mouth, one end is com Port (female port, the male port is inserted into others, and the female port is inserted). Later, desktop computers do not support it com Mouth, there it is com Oral rotation usb Mouth (now there are) console Oral rotation usb (mouth)

Common network devices:

Switch: Communication in the same logical network segment
 Router (enterprise router):
	Communication of different logical network segments
	(GE=Gbps，Gigabit, 100m FE)(WAN Connected to Wan, LAN Port connected to LAN, LAN (with switching function)

Logical network segment: (IP address network segment)
192.168.15.1 192.168.15.200
As long as the first three digits of the IP address are consistent, they are different IPs in the same logical network segment, and they can communicate through the switch; As long as any of the first three numbers is different, they are different logical network segments and need to communicate through routers

Physical segment:
Is the physical connection line in the same network segment

Characteristics of physical network segment:
In different physical network segments, different logical network segments need to be configured;
In the same physical network segment, you need to configure the same logical network segment.

If the two switches want to communicate without interference with each other, it can be solved by connecting the router in the middle (the computer is equipped with IP, and the router also needs to be equipped with IP. The IP address cannot overlap. Generally, the first IP address is allocated to the router; when the router connects the two switches, the first port is equipped with 15.1, and the second port is equipped with 15.2, it will report an error, and it must be equipped with other numbers between 0 and 255 different from 15)

LAN:
The network located in the same routing node is a local area network (if the network enters the maintenance scope of the operator, it will enter the wide area network. The network within its own maintenance scope and its own control node is a local area network)

Network topology:

Schematic diagram of physical connection (for work convenience)( viso	Yitu) (necessary software if the working environment is complex)

Star topology:
advantage:	Easy to implement
		Easy network expansion
		Easy troubleshooting
 Disadvantages:
		High pressure at central node
		High networking cost

Network topology:
	Each node is connected to at least two other nodes
	High reliability and networking cost