This document lists 20 common port numbers and their associated protocols, providing brief descriptions of each. It covers protocols for file transfer (FTP, SSH, Telnet), email (SMTP, POP2/3, IMAP), networking (DNS, BOOTP/DHCP, HTTP, SQL, SMB/CIFS, LDAP, NFS), and secure variants (HTTPS). The port numbers, protocol names and basic functions are provided for each entry.

1. 20 Common port
numbers
&
their purposes

2. Protocol: (FTP)
• Port number (20-21)
• FTP stands for File Transfer Protocol
• Protocol for transferring files over a
network. It supports both anonymous
and password-mediated access.

3. Protocol: (SSH)
• Port number (22)
• SSH stands for Secure Shell
• Its an encrypted remote access tool.
It supports file transfers and
encrypting other protocols.

4. Protocol: (Telnet)
• Port number (23)
• It’s seldom used today, although its
client program, telnet, can be a useful
network diagnostic tool.

5. Protocol: (SMTP)
• Port number (25)
• SMTP stands for Simple Mail
Transfer Protocol
• Main protocol for moving email on
the Internet. The sender initiates
SMTP transfers

6. Protocol: (DNS)
• Port number (42)
• DNS stands for Domain Name Service
• enables computers to look up an IP
address by providing a hostname, or
vice-versa.

7. Protocol: (BOOTP, DHCP)
• Port number (67)
• BOOTP stands for Bootstrap Protocol
• DHCP stands for Dynamic Host
Configuration Protocol
• Both enable a computer on a local network
to help automatically configure other
computers to use a network.

8. Protocol (HTTP)
• Port number(80)
• HTTP stands for Hypertext Transfer
Protocol
• HTTP is the basis of the World Wide
Web

9. Protocol: (POP2 and POP3)
• Port number (109–110)
• POP stands for Post Office Protocol
• It enables a recipient to initiate an
email transfer, it’s often used as the
last leg in email delivery, from a
server to the recipient.

10. Protocol: (SQL)
• Port number (118)
• SQL stands for Structured Query
Language
• Its a network-enabled database interface
language. If you run an SQL server on
your network, client computers can access
and modify that database.

11. Protocol: (SMB/CIFS)
• Port number (137–139)
• SMB stands for Server Message Block
• CIFS stands for Common Internet File
System
• protocols for file and printer sharing, and
Samba implements these protocols in
Linux.

12. Protocol: (IMAP)
• Port number (143, 200)
• IMAP stands for Internet Message Access
Protocol
• Its another recipient-initiated email
transfer protocol, similar to POP. IMAP
makes it easier for recipients to
permanently store and manage email on
the server computer, though.

13. Protocol: (LDAP)
• Port number (389)
• LDAP stands for Lightweight Directory
Access Protocol
• A network protocol for accessing
directories, which in this context are a
type of database.

14. Protocol: (HTTPS)
• Port number (443)
• This protocol is a secure (encrypted)
variant of HTTP.

15. Protocol: (NFS)
• Port number (2049)
• NFS stands form Network File System
• A protocol, and a server of the same name,
for file sharing between Unix and Unix-
like OSs