What is TCP/IP?

     . Transmission Control Protocol/Internet Protocol is the basic communication protocol of the internet.
     . Specifies how data is exchanged over internet by providing end-to-end communication.
     . Handles how data should be broken into packets, addressed, transmitted, routed and received at destination.
     . Each of the two protocols have different functionality.


     . IP Address identifies a device on a computer.
     . This IP address alone is not sufficient to transfer data as computer can run multiple applications.
     . So, IP identifies computer, Port identifies application/service running on computer.
     . Port number is a 16 bit integer ranging from 0 to 65535.
     . Port Numbers are standardized by IANA and they are present in header section of packet which is being transmitted.
     . By these port numbers, the purpose of packet is known. Example:Web, email etc.

 Different TCP/IP ports:

ProtocolPort NumberUsed for:
File Transfer Protocol (FTP)20/21FTP control is handled on port 21 and data is transfered on port 20
Secure Shell (SSH)22To manage network devices securely
Telnet23To manage network devices securely, but it is not as secure as SSH
Simple Mail Transfer Protocol (SMTP)25To transfer email to server
Domain Name System (DNS)53To translate domain names into IP addresses
Dynamic Host Configuration Protocol (DHCP)67/68To assign dynamic IPs in a network
Hyper Text Transfer Protocol (HTTP)80Web browsers
Post Office Protocol (POP)110To retrieve mail from servers
Internet Mail Access Protocol (IMAP)143Retrieves mail from servers, advanced version of POP
Hyper Text Transfer Protocol over SSL (HTTPS)443HTTP in conjunction with SSL
File Transfer Protocol over SSL (FTPS)989FTP in conjunction with SSL