Network models are the basis of computer networks, so questions related to network models are often involved in interviews. Below are some frequently asked interview questions about network models and their corresponding answers.

(A complete set of Java information is attached at the end of the article and can be obtained at any time)

1.How many layers does the OSI (Open Systems Interconnection) model have? Please briefly describe the function of each layer.

Answer:

The OSI model has seven layers: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer.

Physical layer: Responsible for the transmission and reception of physical media, such as voltage, current, etc.

Data link layer: handles the transmission and reception of frames and is responsible for physical addresses and error detection.

Network layer: handles the routing and forwarding of data packets, and is responsible for logical addresses and IP addresses.

Transport layer: Provides end-to-end data transmission, such as TCP and UDP.

Session layer: manages the establishment and maintenance of sessions.

Presentation layer: Responsible for the format and encryption of data.

Application layer: Provides application program interfaces, such as HTTP, FTP, etc.

2. How many layers does the TCP/IP model have? How is it different from the OSI model?

Answer:

The TCP/IP model has four layers: network interface layer, network layer, transport layer and application layer.

Unlike the OSI model, the TCP/IP model merges the presentation layer and session layer into the application layer, and the data link layer and physical layer into the network interface layer. In this way, the TCP/IP model is more simplified and more suitable for the description of Internet protocols.

3. What are three-way handshake and four-way wave? What is their role in TCP connections?

Answer:

The three-way handshake is the process of establishing a TCP connection, including the client sending SYN to the server, the server responding SYN-ACK, and the client sending ACK to establish the connection.

Four waves are the process of closing a TCP connection, including the client sending a FIN to the server, the server responding with an ACK, and then the server sending a FIN to the client, and the client responding with an ACK, completing the closing of the connection.

4. What is the difference between TCP and UDP?

Answer:

TCP (Transmission Control Protocol) is connection-oriented, provides reliable data transmission and ensures the order of data. UDP (User Datagram Protocol) is connectionless-oriented, provides unreliable data transmission, and does not guarantee the order of data.

TCP performs a three-way handshake and four waves, while UDP does not need to establish and close the connection.

TCP has high overhead and is suitable for applications that require reliable transmission, such as Web browsing and file transfer. UDP is suitable for applications that require low latency, such as streaming media and video calls.

5. What are IP addresses and MAC addresses? What's the relationship between them?

Answer:

An IP address is a logical address used to identify a device on a network and is used to route packets across different networks. A MAC address is the physical address of a network adapter and is used to uniquely identify the device within a local network.

Relationship: IP addresses are usually used in higher-level network protocols, while MAC addresses are usually used in the data link layer for local network communications.

6. What is a subnet mask? How to calculate the length of subnet mask and number of hosts?

Answer:

A subnet mask is a method used to divide an IP address, indicating which bits are used for the network part and which bits are used for the host part. It is defined by setting bits in the network part to 1 and bits in the host part to 0.

The length of the subnet mask indicates how many bits are in the network portion and the remaining bits are for the host. The longer the subnet mask length, the fewer hosts and more networks.

7. What are HTTP and HTTPS? What's the difference between them?

Answer:

HTTP (Hypertext Transfer Protocol) is a protocol for transmitting data on the Web, in clear text.

HTTPS (Hypertext Transfer Security) is a secure version of HTTP that encrypts communication through SSL/TLS to protect data privacy and integrity.

Difference: HTTP data is transmitted in clear text and is easily eavesdropped and tampered with; HTTPS data is encrypted and has higher security.

8. What is DNS (Domain Name System)? What does it do?

Answer:

DNS is the Domain Name System, which is used to map human-readable domain names (such as www.example.com) to IP addresses so that computers can find the corresponding server.

The main function of DNS is to perform domain name resolution and convert domain names into IP addresses in order to locate and access servers on the Internet.

9. What are HTTP requests and HTTP responses? What are their common parts?

Answer:

An HTTP request is a message sent by the client to the server to request a specific resource. It usually includes the request method (GET, POST, etc.), URL, HTTP version, request header and request body.

An HTTP response is a message sent by the server to the client to respond to the request and return the resource. It usually includes status code, response headers and response body.

Common HTTP request methods include GET (obtain resources), POST (submit data), PUT (update resources), DELETE (delete resources), etc.

Common HTTP response status codes include 200 (success), 404 (not found), 500 (server internal error), etc.

10. What are Cookies and Sessions? What purpose are they used for?

Answer:

Cookies are small pieces of data sent by the server to the client and stored in the client's browser. It is commonly used to track a user's session information, save user preferences, and authenticate.

Session is a server-side mechanism used to track the user's session state. Typically, Session uses cookies to uniquely identify the user, but the actual data is stored on the server.

11. What is a Cross-Site Request Forgery (CSRF) attack? How to protect against it?

Answer:

A CSRF attack is an attack method that uses a user's logged-in identity to perform malicious operations without their knowledge. The attacker forges requests to allow users to perform actions under their permissions.

Methods to prevent CSRF attacks include checking the Referer header, using CSRF tokens, using the same origin policy and implementing double confirmation.

12. What is RESTful architecture? What are the RESTful principles?

Answer:

RESTful architecture is an architectural style for designing network applications, based on the HTTP protocol.

RESTful principles include resource identification, unified interface, state-independent, hierarchical system, on-demand code, etc.

13. What is TCP congestion control? What is its purpose?

Answer:

TCP congestion control is a mechanism for monitoring and managing congestion on the network to ensure reliable transmission of data.

The purpose is to prevent network congestion, maintain network performance, share network bandwidth fairly, and control the data transmission rate by adjusting the congestion window size.

14. What are HTTP proxy and reverse proxy? What's the difference?

Answer:

An HTTP proxy is an intermediary device between the client and the server that forwards HTTP requests and responses. Proxies are often used for caching, filtering, security, etc.

A reverse proxy is an intermediary device that sits between the server and the client and is used to receive client requests on behalf of the server and route them to the appropriate server. Reverse proxies are commonly used for load balancing and security.

15. What is UDP protocol? How is it different from TCP?

Answer:

UDP (User Datagram Protocol) is a connectionless-oriented transport layer protocol that provides unreliable data transmission. UDP does not establish a connection, has no congestion control, and is suitable for real-time communication.

Unlike TCP, UDP does not provide reliability, flow control, or congestion control, but it has lower latency and less overhead.

16. What are IPv4 and IPv6? What are their main differences?

Answer:

IPv4 (Internet Protocol version 4) and IPv6 (Internet Protocol version 6) are protocols used to identify a computer's location on the Internet.

The main difference is the address length. IPv4 uses 32-bit addresses, while IPv6 uses 128-bit addresses, providing more address space to cope with the problem of IPv4 address exhaustion.

17. What is HTTP/2? How is it different from HTTP/1.x?

Answer:

HTTP/2 is a new version of the HTTP protocol designed to improve performance. It differs from HTTP/1.x in that it introduces features such as multiplexing, header compression, and binary transmission, which reduce network delay.

HTTP/2 provides higher throughput and faster loading speeds by allowing multiple requests and responses to be transmitted simultaneously.

18. What is WebSocket? What is it used for?

Answer:

WebSocket is a protocol for enabling two-way communication, allowing full-duplex communication over a single connection.

Unlike HTTP, WebSocket connections can be initiated not only by the client, but also by the server. It is suitable for applications that require real-time communication, such as online chat, online games, etc.

19. What are HTTP status codes 204 and 304? What do they mean?

Answer:

HTTP status code 204 indicates success, but the response does not contain an entity body. Typically used to acknowledge receipt of a request without returning actual data.

HTTP status code 304 means Not Modified and is typically used with conditional requests. It tells the client that its cached copy is still valid and no need to re-download it.

20. What is HTTPS? Why is it more secure than HTTP?

Answer:

HTTPS is a secure version of HTTP that uses encryption to protect the privacy and integrity of data transmission. It is based on SSL/TLS protocol.

HTTPS is more secure than HTTP because it encrypts data, prevents man-in-the-middle attacks, provides authentication, and ensures communication security.

The questions cover a variety of network models and protocols, including transport layer protocols (TCP, UDP), network layer protocols (IPv4, IPv6), application layer protocols (HTTP, WebSocket), network security, and performance-related topics. Continue to improve your networking knowledge in preparation for interviews. If you have any other area-specific questions, please let me know as well and I'll try to help.