The application layer provides an interface between software running on a computer and network itself.

There are various application layer protocols, majorly used ones are listed below :

HTTP

• Allows to access web page.
• 80 port number

TELNET

• Telnet is used for terminal emulation.
• Allows a user sitting on a remote machine to access the resource of another machine.
• 23 port number

FTP

• Allows you to transfer files fromone machine to another.
• Allows access to both directories and files.
• 20, 21 port number

TFTP

• Is stripped down version of FTP
• Has no directories browsing abilities
• Can only send and receive files
• Uses UDP for data transfer and hence faster but not reliable.
• 69 port number

SNMP

• Simple network management protocol
• Enable a central management of network.
• Using SNMP admin can watch the entire network
• SNMP works with TCP/IP
• It uses UDP for transportation of data
• E.g. Solarwind, whasup gold, HP openner.
• 161 port number

DHCP

• Dynamic host configuration protocol
• Dynamically assign IP address to host
• Works with DORA (Discover Offer Request Acknowledgement) process.
• 67,68 port number.

DNS

• Domain name service
• Resolves fully qualified domain name (FQDN) with IP address.
• Maintain database for IP address and hostname
• 53 port number