A port number is a logical address of each application (way to identify a specific process) or process that uses a network or the Internet to communicate. A port number is used to uniquely identify network-based applications.
Port numbers consist of 16-bit numbers, and these numbers are assigned automatically by the Operating System, manually by the user.
Internet Assigned Numbers Authority (IANA) assigns port numbers.
Here is the list of most common port numbers in networking:
| Port Number | Usage |
|---|---|
| 20 | File Transfer Protocol (FTP) Data Transfer |
| 21 | File Transfer Protocol (FTP) Command Control |
| 22 | Secure Shell (SSH) |
| 23 | Telnet - Remote login service, unencrypted text messages |
| 25 | Simple Mail Transfer Protocol (SMTP) E-mail Routing |
| 53 | Domain Name System (DNS) service |
| 80 | Hypertext Transfer Protocol (HTTP) used in World Wide Web |
| 110 | Post Office Protocol (POP3) used by e-mail clients to retrieve e-mail from a server |
| 119 | Network News Transfer Protocol (NNTP) |
| 123 | Network Time Protocol (NTP) |
| 143 | Internet Message Access Protocol (IMAP) Management of Digital Mail |
| 161 | Simple Network Management Protocol (SNMP) |
| 194 | Internet Relay Chat (IRC) |
| 443 | HTTP Secure (HTTPS) HTTP over TLS/SSL |
For me, the most common port numbers are 80, 443, 20, 21, 22, 23, 25, 67, and 53. If you are working in a computer-related technical field, then you should memorize all these basic networking protocols.
If you are working in Windows based Active Directory then, you should remember all these important port numbers.
| Port Number | Usage |
|---|---|
| 135 | RPC ( Remote Procedure Call) |
| 389 | LDAP |
| 636 | LDAP SSL |
| 3268 | Global Catalog LDAP |
| 3269 | Global Catalog LDAP SSL |
| 53 | Domain Name System (DNS) service |
| 88 | Kerberos |
| 445 | SMB |
Well, Most of the port numbers are mainly used in TCP and UDP-based networks. The highest TCP port number is (2^16 - 1) or 65,535.
To check your port numbers you have to open the command prompt and press (Window + R) and type “netstat -a” on Command Prompt and hit the Enter button. It'll show your active TCP connections. You'll see the port number just after the IP address. There is a colon : that will separate the IP address and port number.
For Example: If the command shows 192.168.0.1:80 then 192.168.0.1 is your IP address and 80 is your port number.
The IP address is a 32-bit address that uniquely identifies any machine over the Internet, while the Port number is the address of the service within the System.
If we combine the IP address and port number then we call it Socket. Socket is the combination of the Port number and IP address, which is used to identify machines and the services within the machine. It works internally and externally and works as a gateway.
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