A port is used to recognize a specific service which is being executed in a computer. To recognize a port and to send packets, 16 bit numbers known as port numbers are used. A port number along with IP address serves as a destination for packets to be sent.
Here are some important port numbers:
- 20, 21: For FTP (File transfer protocol)
- 22: For SSH (Secure Shell)
- 23: For remote login (Telnet)
- 25: For SMTP (Simple mail transfer protocol)
- 53: For DNS (Domain Name System)
- 80: For World Wide Web
- 110: For POP3 (Post office protocol)
- 143: For IMAP (Internet Message Access Protocol)
- 194: For IRC (Internet relay chat)
- 443: For HTTPS (HTTP secure)
- 532: For Usenet newsgroups
DNS (Domain Name System): Domain name system is used to translate domain name to its corresponding IP address. It is used to simplify the access of a IP address. For a person, it is easier to remember a domain name than an IP address. However, browsers and other internet tools use IP address for various tasks. DNS is used for translating a domain name and then its sends IP address to the browsers and other tools as per the requirements.