Network basic Learning of Linux Operation and maintenance

Network1.5

Transport layer:

The role of the transport layer:

The IP layer provides point-to-point connectivity

The transport layer provides end-to-end connectivity

Transport layer protocols:

TCP:

-Transmission control protocol;-reliable, connection-oriented protocol;-- low transmission efficiency

UDP:

-- user Datagram protocol;-- unreliable, connectionless services;-- High transmission efficiency

How the TCP protocol works:

Encapsulation format of TCP

TCP handshake and disconnect: three-way handshake, four disconnect

Flow control mechanism of TCP:-- sliding window;-- congestion control

Error control of TCP: (three):-- checksum;-- confirm;-- timeout

Timer for TCP:

Retransmission timer: in order to control lost data segments

Stick to the timer: to prevent zero window deadlock

Keep alive timer: prevent long idle time between two TCP connections

Time waiting timer: used during the termination of the connection. When the last ack is sent, the connection is not closed immediately, but wait for a period of time to ensure that duplicate FIN segments can be received.

Application of TCP:

FTP-port number 21muri-file transfer protocol for uploading and downloading

Telnet-- port number 23-used for remote login. By connecting to this port of the target computer, the management computer can be controlled remotely after verification.

SMTP-- port number 25muri-simple Mail transfer Protocol for sending mail

DNS-- port number 53Murray-Domain name service. When users enter the name of the website, DNS is responsible for resolving them to IP addresses.

HTTP-- port number 80muri-hypertext transfer protocol to realize the transmission of hypertext on the network

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How the UDP protocol works:

Encapsulation format of UDP:

Application of UDP:

TFTP-- port number 69Pak-trivial file transfer protocol

DNS-- port number 53muri-domain name service

NTP-- port number 123mura-network time protocol

RPC-- port number 111Mui-remote process control

Flow and error Control of UDP

-- UDP has no flow control mechanism

-- UDP provides error control only by checksum

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Application layer

The role of the application layer

Work with applications to exchange application-specific data using the basic network

Common application layer protocols:

DNS,SMTP,pop3,HTTP,HTTPS,Telnet,FTP,TFTP

DNS: domain name system

-- used to complete the mapping between domain names and IP addresses

-- Port number is TCP or UDP53