1.3 Network Basics and Protocols

Network Foundations and Protocols

1. Network overview

• Definition and function of network: Explain that a computer network is a system in which multiple computers and devices are connected together to realize data exchange and resource sharing through communication links.
• Network Topology: Introduces network topologies, such as star, bus, ring, and mesh, as well as the characteristics and applicable scenarios of each topology.
• Network protocol: Explain that network protocols are the rules and conventions for data transmission and communication in the network to ensure the reliability and accuracy of data.

2. OSI model and TCP/IP model

• OSI model: A detailed introduction to the OSI (Open Systems Interconnection) model, including the seven-layer layered structure (physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer), and the functions of each layer and agreement.
• TCP/IP Model: Explains the TCP/IP (Transmission Control Protocol/Internet Protocol) model, including the four-layer hierarchy (network interface layer, network layer, transport layer, and application layer), and compares it to the OSI model.

3. IP address and subnet mask

• IP Address: Introduces the definition and classification of IP addresses, including the format and representation of IPv4 and IPv6 addresses.
• Subnet mask: Explain the function and principle of the subnet mask, which is used to divide the network and host parts of the IP address.
• IP Address Assignment: Explains how IP addresses are assigned, including manual configuration and Dynamic Host Configuration Protocol (DHCP).

4. Network equipment and data transmission

• Network Devices: Describes common network devices such as switches, routers, gateways, firewalls, and network adapters, and their roles and functions in a network.
• Data transmission: Explain the transmission process of data in the network, including the encapsulation, sending and receiving of data frames, as well as the forwarding and routing of data between different network devices.

5. Common network protocols

• TCP and UDP: Compare the characteristics and application scenarios of TCP (Transmission Control Protocol) and UDP (User Datagram Protocol), and their different transmission methods above the application layer.
• HTTP and HTTPS: Explain the difference and use of HTTP (Hypertext Transfer Protocol) and HTTPS (Hypertext Transfer Protocol Secure Sockets Layer), and the security of HTTPS in network communication.

6. Internet Security

• Network attack and defense: introduces common network attack methods, such as DDoS (distributed denial of service attack), DNS hijacking, ARP spoofing, etc., as well as defense measures and security strategies.
• Firewalls and Intrusion Detection Systems: Explain the role and principles of firewalls and intrusion detection systems (IDS), which are used to protect networks from malicious attacks and unauthorized access.

7. Wireless network

• Wireless network overview: introduces the basic principles and classifications of wireless networks, including Wi-Fi (wireless local area network), Bluetooth and mobile communication networks, etc.
• Wireless Network Security: Explains the security challenges of wireless networks, and common wireless security protocols such as WEP, WPA, and WPA2.

Through the study of this chapter, readers will understand the basic concepts and principles of the network, as well as common network protocols and security mechanisms, laying a solid foundation for the in-depth study and practice of subsequent chapters.

network overview

Computer network is an indispensable infrastructure in modern information society. It connects multiple computers and devices to realize data transmission and communication. The role of the network is far more than connecting computers. It carries the development of many fields such as the Internet, cloud computing, and the Internet of Things. In operation and maintenance, the network is the basis for the stable operation of the system and the key to data transmission and application interaction.

Network topology

Network topology refers to the physical or logical structure that connects the various nodes in a computer network. Different network topologies have different effects on data transmission, communication between nodes and system reliability. Common network topologies include:

1. Star topology: centered on a central node (switch or hub) to which all other nodes are directly connected. This topology is simple and easy to manage, but the failure of the central node will lead to the paralysis of the entire network.
2. Bus topology: All nodes are connected to the same transmission line, and the transmission medium is shared between nodes. Bus-type topologies are less expensive, but signal conflicts and performance issues can occur when there are many nodes.
3. Ring topology: Each node is connected to two adjacent nodes to form a ring structure. In ring topology, data is transmitted cyclically on the ring, but when one connection fails, the entire ring will be interrupted.
4. Mesh topology: each node is directly connected to other nodes to form a fully connected structure. Mesh topologies are highly redundant and fault-tolerant, but costly and difficult to manage.

Different topologies can be selected according to actual needs. For example, small local area networks often use star or bus topology, while large-scale Internet usually uses mesh topology to provide higher reliability and fault tolerance.

Network protocol

In a computer network, in order to achieve reliable data transmission and communication, certain rules and conventions need to be followed, and these rules and conventions are called network protocols. The network protocol defines the data encapsulation format, transmission mode, error detection and correction mechanism, etc., to ensure that the data can be transmitted correctly and efficiently. Common network protocols are:

1. TCP/IP protocol: is the most commonly used protocol suite on the Internet, including Transmission Control Protocol (TCP) and Internet Protocol (IP). TCP is responsible for the reliable transmission of data, while IP is responsible for the routing and addressing of data packets.
2. HTTP protocol: Hypertext Transfer Protocol, used to transmit data between web browsers and web servers, is the basic protocol of web communication.
3. DNS protocol: domain name system protocol, which is used to resolve domain names into IP addresses, so as to realize the conversion of host names to IP addresses.
4. DHCP protocol: Dynamic Host Configuration Protocol, used to automatically assign IP addresses and other network configuration information, simplifying the configuration process of network devices.

The continuous development and improvement of network protocols enables computer networks to operate more efficiently and reliably, providing users with a better network experience.

Through a deep understanding of network concepts and protocols, O&M personnel can better grasp the basic principles and functions of the network, and thus perform network management and troubleshooting more efficiently. At the same time, as the core infrastructure of the modern information society, the importance and role of the network cannot be ignored. Operation and maintenance personnel need to continuously learn and update network knowledge to adapt to the ever-changing network environment and needs.

OSI model

The OSI (Open Systems Interconnection) model is a reference model for communication protocols in computer networks. It divides the network communication process into seven different layers, and each layer is responsible for specific functions and tasks. By defining specific protocols and specifications at each layer, the OSI model enables interoperability between different devices and systems.

1. Physical Layer : This layer is the bottom layer of the network and is mainly responsible for the physical transmission of data, including data transmission media, electrical characteristics, and interface specifications.
2. Data Link Layer (Data Link Layer) : This layer is responsible for assembling data frames transmitted by the physical layer into data packets, and performing addressing and error detection of physical addresses (MAC addresses).
3. Network Layer (Network Layer) : The network layer is responsible for the routing and forwarding of data packets, uses IP addresses to identify devices in the network, and selects the appropriate path to send data packets to their destinations.
4. Transport Layer (Transport Layer) : The transport layer provides end-to-end data transmission services, including reliable transmission (such as TCP) and connectionless transmission (such as UDP).
5. Session Layer (Session Layer) : This layer is responsible for establishing, managing, and terminating session connections between applications, as well as implementing data synchronization and checkpoint functions.
6. Presentation Layer : The presentation layer is responsible for data format conversion, encryption and decryption, and data compression to ensure that the application can correctly interpret the received data.
7. Application Layer (Application Layer) : The application layer is the layer where users interact directly with applications, including various applications and services, such as email, file transfer, web browser, etc.

TCP/IP model

The TCP/IP (Transmission Control Protocol/Internet Protocol) model is a more commonly used network model in practical applications. It divides the network communication process into four levels, and the corresponding relationship with the OSI model is as follows:

• Network interface layer (corresponding to the physical layer and data link layer of the OSI model): responsible for the connection between physical devices and the transmission of data frames, and realizes physical addressing and error detection.
• Network layer (corresponding to the network layer of the OSI model): responsible for IP address allocation and routing selection, and realizing the transmission of data packets in the network.
• Transport layer (corresponding to the transport layer of the OSI model): Provides end-to-end reliable or connectionless transport, including TCP and UDP protocols.
• Application layer (corresponding to the session, presentation and application layers of the OSI model): includes various applications and services, and realizes the interaction between users and network services.

Compared with the OSI model, the TCP/IP model combines the functions of the presentation layer and the session layer into the application layer, simplifies the structure of the network protocol, and is more in line with the needs of practical applications. Therefore, in practical applications, the TCP/IP model is widely used, especially in the Internet.

An in-depth understanding of the OSI model and TCP/IP model will help O&M personnel better understand the principles and mechanisms of network communication, and improve the capabilities of network troubleshooting and network optimization. At the same time, understanding the corresponding relationship between these two models will help to better understand and apply modern network technology.

IP address

1. Definition and classification

An IP address is a set of numbers used to identify and locate devices on a computer network, uniquely identifying each device on the network. There are two versions of IP addresses: IPv4 (Internet Protocol version 4) and IPv6 (Internet Protocol version 6).

• IPv4 address: It consists of 32 binary digits, usually represented by four decimal numbers, and the value range of each number is 0-255, for example: 192.168.0.1.
• IPv6 address: It consists of 128 binary digits, usually represented by eight groups of four-digit hexadecimal numbers, and each group of numbers is separated by colons, for example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334.

2. Classification of IP addresses

IPv4 addresses can be divided into the following categories according to their network part and host part:

• Class A address: used for large networks, the network part occupies 8 bits, and the host part occupies 24 bits.
• Class B address: used for medium-scale networks, the network part occupies 16 bits, and the host part occupies 16 bits.
• Class C address: used for small networks, the network part occupies 24 bits, and the host part occupies 8 bits.
• Class D address: used for multicast, the network part occupies the first 4 bits, and the last 28 bits are used for multicast addresses.
• Class E addresses: Reserved addresses for experiments and research.

subnet mask

1. Function and principle

A subnet mask is used to divide the network and host portions of an IP address. It is a 32-bit binary number, which is bitwise ANDed with the IP address to divide the IP address into a network address and a host address.

In the subnet mask, the network part is represented by 1, and the host part is represented by 0. For example, for the IP address 192.168.0.1 and the subnet mask 255.255.255.0, the network address is 192.168.0.0 and the host address is 0.0.0.1 through bitwise AND operation.

2. The format of the subnet mask

The subnet mask is usually indicated with the IP address, using a slash followed by a number to indicate the length of the network prefix. For example, 192.168.0.1/24, where 24 represents the length of the network part, that is, the first 24 bits of the subnet mask are 1, and the last 8 bits are 0.

IP address assignment

1. Manual configuration

Manual configuration is the most common method of IP address assignment, where administrators manually assign unique IP addresses to each device. This method is suitable for small-scale network and specific device configuration, but it is not practical for large-scale network management.

2. Dynamic Host Configuration Protocol (DHCP)

DHCP is an automatic IP address allocation method. The DHCP server automatically assigns IP addresses and other network configuration information to devices in the network, such as subnet mask, gateway, and DNS server.

The advantage of DHCP is that it simplifies the management and configuration of IP addresses and reduces the possibility of conflicts and duplicate assignments. It is suitable for large-scale networks and dynamic device connection situations.

A deep understanding of the concepts and principles of IP addresses and subnet masks is very important for understanding the address planning and configuration of computer networks. Grasp the different ways of IP address allocation, which is helpful for effective management and maintenance of devices in the network

Internet equipment

1. switch

A switch is a common networking device used to connect multiple computers and other network devices in a local area network (LAN). It can forward data packets according to the MAC address of the device, realize direct communication between devices, and improve network transmission efficiency and speed.

2. Router

A router is a device used to connect different networks. It can forward data packets according to IP addresses to realize communication between different networks. Routers play a vital role in the internet, helping packets of data find the correct path to their destination.

3. Gateway

A gateway is a device or computer that connects different networks and acts as an entry or exit into a network, transferring data from one network to another. Gateways are usually used to connect local area networks and wide area networks to realize communication between local networks and external networks.

4. Firewall

A firewall is a device used to protect network security. It can monitor and control network traffic, and prevent unsafe data packets from entering the network, thereby preventing malicious attacks and illegal access.

5. Network Adapter

A network adapter is a hardware device used to connect a computer to a network. It is responsible for converting data generated or received by the computer into a format suitable for transmission on the network, enabling the computer to communicate with the network.

data transmission

The transmission of data in a computer network is a complex process involving the cooperative work of multiple network devices and protocols. The main process includes:

1. Data frame encapsulation

Data frame is the basic unit of data transmission in the network. When sending data, the data is encapsulated into a data frame, including fields such as destination MAC address, source MAC address, data and checksum.

2. Data sending

The sender sends the encapsulated data frame to the network, and finds the corresponding receiver device according to the target MAC address.

3. Data reception

After receiving the data frame, the receiving device identifies whether it is its own data according to the target MAC address, and extracts the data for processing.

4. Data forwarding and routing

If data needs to be transmitted across multiple network devices, the router will search the routing table according to the destination IP address to determine the forwarding path of the data.

5. Data transfer completed

After a series of forwarding and routing, the data is finally transmitted to the destination, and the receiving device decapsulates the data, and performs corresponding processing and response.

Understanding the functions and functions of network devices, as well as the data transmission process in the network, helps us understand the working principle of computer networks and the mechanism of data communication. At the same time, this also provides the basic knowledge for network troubleshooting and network performance optimization.

Common Network Protocols

1. TCP (Transmission Control Protocol) and UDP (User Datagram Protocol)

TCP and UDP are two common transport layer protocols used to transmit data in computer networks. They differ in functionality and usage scenarios:

• TCP (Transmission Control Protocol): TCP is a connection-oriented protocol that establishes a connection before data transmission to ensure the reliability and sequence of data transmission. TCP uses confirmation mechanism and retransmission mechanism to ensure the accurate transmission of data, which is suitable for applications that require reliable transmission, such as web browsing, email and file transmission.
• UDP (User Datagram Protocol): UDP is a connectionless protocol that sends data packets directly without establishing a connection, so the transmission speed is faster. However, UDP does not guarantee the reliability and sequence of data, and is suitable for applications that require high transmission speed but low data accuracy, such as audio and video transmission.

2. HTTP (Hypertext Transfer Protocol) and HTTPS (Hypertext Transfer Protocol Secure Sockets Layer)

HTTP and HTTPS are two commonly used application layer protocols for transmitting hypertext and web page information in the network. They differ in terms of security:

• HTTP (Hypertext Transfer Protocol): HTTP is a stateless protocol that transmits data in plain text and has poor security. HTTP is fine for general web browsing and resource fetching, but not for transferring sensitive information such as passwords and personal data.
• HTTPS (Hypertext Transfer Protocol Secure Sockets Layer): HTTPS adds security on the basis of HTTP, and encrypts data through the SSL/TLS encryption protocol to ensure the security and privacy of data during transmission. HTTPS is suitable for websites that need to protect sensitive information, such as e-commerce, online payments, and user logins.

By understanding the characteristics and applicable scenarios of TCP and UDP, as well as the difference and security between HTTP and HTTPS, we can choose the appropriate protocol according to the application requirements to ensure the security and efficiency of data transmission in the network. At the same time, understanding these protocols will also help us better troubleshoot and optimize network performance.

cyber security

1. Cyber ​​attack and defense

A cyber attack is any malicious act against computer networks and systems aimed at disrupting, altering, stealing or denying service. Common cyber attacks include:

• DDoS (Distributed Denial of Service Attack): The attacker sends a large number of requests to the target server by controlling multiple computers, causing the server resources to be exhausted and the service to be unavailable.
• DNS hijacking: Attackers tamper with DNS resolution results, direct user domain name requests to malicious websites, implement phishing attacks or hijack user information.
• ARP spoofing: An attacker forges an ARP response on the local network to trick other computers into sending data to the wrong MAC address, thereby stealing data or conducting a man-in-the-middle attack.

To defend against these cyber attacks, the following security measures and strategies can be adopted:

• Use a firewall: Configure a firewall to restrict network traffic, allowing only authorized packets to pass through, thereby preventing unauthorized access and attacks.
• Strengthen network authentication: Use authentication and access control mechanisms to ensure that only authorized users can access sensitive data and resources.
• Implement data encryption: use encryption protocols such as SSL/TLS to protect the security of data during transmission and prevent data from being stolen or tampered with.

2. Firewall and Intrusion Detection System

A firewall is a network security device used to monitor and control network traffic to prevent unauthorized access and attacks. The firewall can filter data packets according to predefined rules and policies to protect the network from malicious attacks.

Intrusion Detection System (IDS) is a security device used to monitor abnormal behavior and attack attempts in the network. IDS can monitor network traffic in real time, identify and report potential security threats, and help detect and respond to network attacks early.

The combination of firewall and intrusion detection system can effectively improve network security and prevent various network attacks. The firewall is responsible for blocking packets that do not comply with the rules, while the intrusion detection system is responsible for discovering potential attacks. Through comprehensive application of these security measures, the network can be protected from malicious attacks and ensure the stability and security of the network.

wireless network

1. Wireless Network Overview

A wireless network is a network that transmits data through wireless signals, and is widely used in fields such as mobile communications, Internet access, and the Internet of Things. Common wireless networks include:

• Wi-Fi (Wireless Local Area Network): Wi-Fi is a wireless local area network technology based on the IEEE 802.11 standard that provides high-speed wireless Internet access.
• Bluetooth: Bluetooth is a short-range wireless communication technology commonly used for data transmission and connection between devices.
• Mobile communication network: A mobile communication network is a wireless network that provides mobile telephony and data communication services, including different mobile communication standards such as 2G, 3G, 4G, and 5G.

The advantage of wireless network is that it can provide convenient mobility and flexibility, so that users can realize data transmission and communication without physical connection. However, wireless networks also face some challenges, such as signal interference, data security, and network capacity limitations.

2. Wireless network security

The security of wireless networks has always been an important issue, because wireless signals are easily eavesdropped and interfered. To protect the security of wireless networks, common wireless security protocols include:

• WEP (Wired Equivalent Privacy): WEP was an early wireless security protocol, but is now deprecated due to its vulnerabilities and vulnerabilities.
• WPA (Wi-Fi Protected Access): WPA is an improved version of WEP, which provides stronger data encryption and authentication mechanisms and enhances the security of wireless networks.
• WPA2: WPA2 is currently the most commonly used wireless security protocol, using the AES (Advanced Encryption Standard) encryption algorithm to provide higher security and protection levels.

Although WPA2 is relatively secure, it is not absolutely secure. In order to further strengthen the security of the wireless network, other measures can also be taken, such as hiding the network name (SSID), enabling MAC address filtering, using a virtual private network (VPN), and so on.

Generally speaking, the security of wireless networks needs to comprehensively consider various measures such as physical security, encryption protocol, authentication mechanism and network monitoring to ensure the security and confidentiality of wireless communication and data transmission.