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Computer Networks
Knowledge Summary
Network Classification
| Type | English | Range |
|---|---|---|
| Local Area Network | LAN | Hundreds to thousands of meters |
| Metropolitan Area Network | MAN | A city |
| Wide Area Network | WAN | A country or the whole world |
OSI Seven-Layer Model
From top to bottom: Application Layer, Presentation Layer, Session Layer, Transport Layer, Network Layer, Data Link Layer, Physical Layer
TCP/IP Four-Layer Model
| Layer | Corresponding OSI Layers | Common Protocols |
|---|---|---|
| Application Layer | Application + Presentation + Session | HTTP, FTP, DNS, SMTP |
| Transport Layer | Transport Layer | TCP, UDP |
| Network Layer | Network Layer | IP, ICMP |
| Network Interface Layer | Data Link + Physical | Ethernet |
IP Addresses
- IPv4: 32 bits, such as
192.168.1.1 - IPv6: 128 bits
- Subnet mask: used to distinguish the network part from the host part
Frequently Tested Knowledge Points
- TCP: connection-oriented, reliable transmission (three-way handshake, four-way termination)
- UDP: connectionless, unreliable but faster
- DNS: resolves domain names into IP addresses
- HTTP: HyperText Transfer Protocol, default port 80
- HTTPS: HTTP + SSL/TLS encryption, default port 443