A port number is communication endpoint with a computer network. TCP stands for Transmission Control Protocol is the suite of communications protocols used for connecting web hosting servers and transmitting data over networks on the Internet. IANA (Internet Assigned Numbers Authority) has assigned specific numbers to these ports, one can access these ports by entering this assigned number in the address bar. This number should be typed after ‘domainname.com:’ in the address bar of browser. Following is the list of few most frequently used TCP ports. The range of port numbers is very large (0 to 65536) but only few of them are reserved for privileged services and designated as well-known ports which are classified in the range from 0 to 1080.
| Port No | Description |
| 1 | TCP Port Service Multiplexer (TCPMUX) |
| 5 | Remote Job Entry (RJE) |
| 7 | ECHO |
| 18 | Message Send Protocol (MSP) |
| 20 | FTP — Data |
| 21 | FTP — Control |
| 22 | SSH Remote Login Protocol |
| 23 | Telnet |
| 25 | Simple Mail Transfer Protocol (SMTP) |
| 29 | MSG ICP |
| 37 | Time |
| 42 | Host Name Server (Nameserv) |
| 43 | WhoIs |
| 49 | Login Host Protocol (Login) |
| 53 | Domain Name System (DNS) |
| 69 | Trivial File Transfer Protocol (TFTP) |
| 70 | Gopher Services |
| 79 | Finger |
| 80 | HTTP |
Rest of the well-known ports are given in the next post.