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2025-02-02 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Network Security >
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Shulou(Shulou.com)06/01 Report--
I. Classification of practical applications in the network
Chunked data streams: FTP, TFTP, inventory updates
No need for direct human interaction
Bandwidth is important, but not a critical factor
Interactive data flow: inventory query, database update
Human-computer interaction
Response time
Factual application data stream: VoIP video
Human interaction
End-to-end delay is critical
II. Network topology classification
At present, they are all star-shaped in practice, and the first two are only theoretical concepts.
The picture above is an extended star. Advantages: no center, distributed. High availability to avoid network paralysis caused by a single point of failure.
Third, OSI seven-layer model
◆ understands the flow of end-to-end data transmission
Hierarchical advantages: 1. Promote standardization and allow suppliers to develop independently.
2. Each layer is independent, and the network operation is divided into low complex thinking units.
3. Good flexibility. Changes in one layer will not affect other layers.
4. each layer communicates up and down the adjacent layer through an interface.
4. TCP\ IP protocol stack
◆ data transmission is encapsulated from top to bottom, and then unencapsulated when received by the peer.
◆ indicates the last agreement. Layer Transport layer: Port number; layer Network layer: TCP UDP; layer Network access layer: IP (0800)
◆ PDU (protocol data unit) each layer uses its own layer protocol to communicate with each other's corresponding layer.
The information exchanged by the protocols of each layer at the peer layer is called the protocol data unit.
Upper layer-message
Transport layer-segment
Network layer-packet
Data Link layer-frame
Physical layer-bit
◆ Application layer Overview: http https
◆ transport layer
● TCP encapsulation format
● common port number: FTP TCP21 file transfer protocol for uploading and downloading
Telnet TCP23
SMTP TCP25 simple Mail transfer Protocol
DNS 53 domain name protocol, which resolves the website name into an IP address, which is usually UDP when the TCP server is synchronized
TFTP UDP69 simple File transfer Protocol
SNMP UDP161; RIP UDP520
NTP UDP123 Network time Protocol
RPC UDP111 remote procedure call
◆ UDP encapsulation format
◆ Network layer Overview: IP
● IP header format IP protocol number 6-> TCP;IP protocol number 17-> UDP
● ICMP protocol
Hierarchical understanding: classified by encapsulation: if understood as 4 layers encapsulated on top of IP
Classified by service object: three-tier service is three-tier ICMP and IP service, so it is three-tier.
◎ ICMP checks whether the network is unblocked. It can be divided into two categories: 1 poor multiple messages and 2 informational messages.
For example, ping belongs to information messages. Trace route is an error message.
Differences in the network layer transport layer (problems encountered in the interview): the transport layer provides logical communication for processes running on different hosts; network layer protocols provide logical communication for different hosts
Communication between processes in the transport layer, and communication between end-to-end IP in the network layer.
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