Shulou(Shulou.com)06/01 Report--

I. Transport layer

The role of the transport layer

The transport layer provides an end-to-end connection (the IP layer provides a point-to-point connection) to protect the data transmission of the application layer.

Transport layer protocol

TCP (Transmission Control Protocol) transmission control protocol. The protocol is a reliable and connection-oriented protocol, which can transmit a large amount of data stably and for a long time.

UDP (User Datagram Protocol) user Datagram protocol. The protocol is an unreliable and connectionless service. The transmission speed of the protocol is fast, but it is unstable and easy to lose packets. In general, it is mainly used for applications with low latency.

Application of TCP and UDP

-- Application of TCP:

FTP-- File transfer Protocol for uploading and downloading

Telnet-- is used for remote login. By connecting to this port of the target computer through l, you can remotely control and manage the target computer after verification.

SMTP-- simple Mail transfer Protocol, used to send mail

DNS-- domain name service, when the user enters the name of the website, DNS is responsible for resolving it to the IP address. The port number used in this process is 53.

HTTP-- hypertext transfer protocol, through HTTP to achieve the transmission of hypertext on the network.

-- Application of UDP:

TFTP-- trivial File transfer Protocol, port number is 69

NTP-- network time protocol, port number is 123,

RPC-- remote procedure call, port number is 111,

4.Port port number

16 bit are occupied in the message, so the range of port number is 0mm 65535.

-- well-known port: tcp 80, indicating the application-web

Tcp 23, which represents the application-telnet

-- Random port: the port range is above 1024.

2. Application layer

The role of the application layer

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

Application layer protocol

Common application layer protocols are: DNS, SMTP and POP3, HTTP and HTTPS, Telnet, FTP and TFTP

-- DNS:Domain Name System domain name system. It is used to complete the mapping between domain name and IP address. The port number is 53 of TCP or UDP.

SMTP:Simple Mail Transfer Protocol simple Mail transfer Protocol. Used to send and receive mail, port number 25.

-- POP3:Post Office Protocol v3 Post Office Protocol version 3. Used for the client to accept mail, port number 110.

HTTP:Hyper Text Transfer Protocol Hypertext transfer Protocol. Used to transmit data such as plain text, hypertext, audio and video used by Internet browsers. The port number is 80 of TCP.

-- HTTPS: secure Hypertext transfer Protocol, developed based on HTTP, provides encryption to ensure the privacy and integrity of messages. The port number is 443.

-FTP:File Transfer Protocol File transfer Protocol. The most widely used file transfer application, with port numbers TCP 21 and 20

-- TFTP:Trivial File Transfer Protocol simple File transfer Protocol, which is used to transfer trivial files with port number UDP 69.

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