Application Layer Protocols

Application Layer Protocols

The application layer may be a layer within the Open Systems Interconnection (OSI) seven-layer model and within the TCP/IP protocol suite. It consists of protocols that target process-to-process communication across Associate in Nursing information science network and provides a firm communication interface and end-user services.

FTP (File Transfer Protocol)

  • FTP is File Transfer Protocol.
  • It used to exchange files on the internet.
  • To enable the data transfer FTP uses TCP/IP, FTP is most commonly used to upload and download files from the internet.
  • FTP can be invoked from the command prompt or some graphical user interface.
  • FTP also allows to update (delete, rename, move, and copy) files at a server.
  • It uses a reserved port no 21.


  • Dynamic Host Configuration Protocol (DHCP) is used assigning IP addresses to computers in a network.
  • The IP addresses are assigned dynamically.
  • Certainly, using DHCP, the computer will have a different IP address every time it is connected to the network.
  • In some cases the IP address may change even when the computer is in network.
  • This means that DHCP leases out the IP address to the computer for sometime.
  • Clear advantage of DHCP is that the software can be used to manage IP address rather than the administrator.


  • The Hypertext Transfer Protocol (HTTP) is used to access the data on WWW(World Wide Web).
  • The functions of HTTP are the combination of FTP (File Transfer Protocol) and SMTP (Simple Mail Transfer Protocol).
  • HTTP is similar to FTP, because it uses only one TCP connection (data is transferred between Client and Sever).
  • In SMTP, the messages are stored and then forwarded to the destination, but the HTTP messages are delivered immediately.
  • HTTP uses the services of TCP on well-known port 80.


  • It is an application layer protocol, which can be used on the internet or LAN(Local Area Network).
  • It provides a bi-directional interactive text oriented communication service by using virtual terminal connection.
  • Telnet is basically a client server protocol, which is based on a reliable connection- oriented transport.
  • It uses a port number 23, to establish the connection with TCP (Transmission Control Protocol).

SMTP (Simple Mail Transport Protocol)

  • It is an internet standard for e-mail Transmission.
  • SMTP connections are secured with SSL (Secure Socket Layer).
  • In SMTP, the messages are stored and then forwarded to the destination.
  • SMTP uses a port number 25 of TCP.

CCNA Application Layer


The Trivial File Transfer Protocol (TFTP) is the stripped-down, stock version of FTP, but it’s the protocol of choice if you know exactly what you want and where to find it. It’s a technology for transferring files between network devices, and is a simplified version of FTP


tftp [ options... ] [host [port]] [-c command]


It stands for network file system.It allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. This enables system administrators to consolidate resources onto centralized servers on the network.


service nfs start


It stands for Simple Mail Transfer Protocol.It is a part of TCP/IP protocol.Using a process called “store and forward,” SMTP moves your email on and across networks. It works closely with something called the Mail Transfer Agent (MTA) to send your communication to the right computer and email inbox.


MAIL FROM:<[email protected]?


It stands for Line Printer Daemon.It is designed for printer sharing.It is the part that receives and processes the request. A “daemon” is a server or agent.


lpd [ -d ] [ -l ] [ -D DebugOutputFile]

 X window:

It defines a protocol for the writing of graphical user interface–based client/server applications. The idea is to allow a program, called a client, to run on one computer. It is primarily used in networks of interconnected mainframes.


Run xdm in runlevel 5


It stands for Simple Network Management Protocol.It gathers data by polling the devices on
the network from a management station at fixed or random intervals, requiring
them to disclose certain information.It is a way that servers can share information about their current state, and also a channel through which an administer can modify pre-defined values.

snmpget -mALL -v1 -cpublic snmp_agent_Ip_address sysName.0


It stands for Domain Name Service.Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name might translate to


ipconfig /flushdns


It stands for Dynamic Host Configuration Protocol (DHCP).It gives IP addresses to hosts.There is a lot of information a DHCP server can provide to a host when the host is registering for an IP address with the DHCP server.


clear ip dhcp binding {address | * }

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