8 common application layer protocols: 1. DNS domain name system; 2. FTP file transfer protocol; 3. Telnet remote terminal protocol; 4. HTTP hypertext transfer protocol; 5. SMTP email protocol; 6 , POP3 mail reading protocol; 7. SNMP simple network management protocol; 8. TFTP simple file transfer protocol.
The operating environment of this tutorial: Windows 10 system, Dell G3 computer.
The application layer protocol defines how application processes running on different end systems transfer messages to each other.
Commonly used protocols at the application layer
1. DNS: Domain Name System
DNS is used by the Internet A naming system that converts human-friendly machine names into IP addresses.
Currently top-level domain name TLDs are divided into three categories: national top-level domain names nTLDs; general top-level domain names gTLDs; infrastructure domain names
Domain name servers are divided into four types: root domain name servers; top-level domain name servers ;Local domain name server; authority domain name server.
2. FTP: File Transfer Protocol
FTP is the most widely used file transfer protocol on the Internet. FTP provides interactive access, allows customers to specify file types and formats, and allows files to have access rights. FTP is different from TCP.
3. Telnet: Remote Terminal Protocol
Telnet is a simple remote terminal protocol, which is also the official standard of the Internet. Also known as the terminal emulation protocol.
4. HTTP: Hypertext Transfer Protocol
HTTP is a transaction-oriented application layer protocol. It is an important foundation for the reliable exchange of files on the World Wide Web. http uses connection-oriented TCP as the transport layer protocol to ensure reliable transmission of data.
5. SMTP: Email Protocol
is the Simple Mail Transfer Protocol. SMTP specifies how information should be exchanged between two SMTP processes that communicate with each other. There are three stages of SMTP communication: connection establishment, email transmission, and connection release.
6. POP3: Mail Reading Protocol
POP3 (Post Office Protocol 3) protocol is usually used to receive emails.
7. SNMP: Simple Network Management Protocol
SNMP consists of three parts: SNMP itself, management information structure SMI and management information MIB.
SNMP defines the packet format exchanged between management stations and agents. SMI defines general rules for naming object types and encoding objects and object values. MIB creates named objects in managed entities and specifies types.
8. TFTP: Simple File Transfer Protocol
TFTP is one of the TCP/IP protocol suites used for simple file transfer between the client and the server. Protocol that provides uncomplicated and inexpensive file transfer services. The port number is 69.
TFTP is a simple protocol for transferring files. It is implemented based on the UDP protocol, but we are not sure that some TFTP protocols are based on other transmission protocols. This protocol is designed for small file transfers. Therefore it does not have many of the features of the usual FTP, it can only get or write files from the file server, it cannot list directories, it does not authenticate, and it transfers 8-bit data. There are three modes in transmission: netascii, which is an 8-bit ASCII code form, and the other is octet, which is an 8-bit source data type; the last mail is no longer supported, and it returns the returned data directly to the user. Not saved as a file.
Features:
Data messages are all 512 bytes (the last time can be ≤512Bytes)
Data messages Numbered by serial number, starting from 1
Supports ASCII code and binary transmission (FTP also supports)
Can read and write files
First part is simple
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