18 Essential Network Ports: A Must-Know Guide for Secure and Efficient IT Operations

Understanding key network ports is crucial for IT professionals, network engineers, and cybersecurity teams. Here are some essential ones:

FTP (File Transfer Protocol) – TCP/21: Used for transferring files between clients and servers.
SSH (Secure Shell) – TCP/22: Provides a secure channel for remote login and command execution.
Telnet – TCP/23: Offers unencrypted, text-based remote login (Use SSH instead for security).
SMTP (Simple Mail Transfer Protocol) – TCP/25: Handles email sending between clients and mail servers.
DNS (Domain Name System) – UDP/TCP/53: Resolves domain names to IP addresses and vice versa.
DHCP Server – UDP/67: Assigns IP addresses and network configurations to clients.
DHCP Client – UDP/68: Allows client devices to receive IP addresses from the DHCP server.

Mastering these ports is key to managing networks effectively and ensuring security.

You Should Know:

1. FTP (File Transfer Protocol) – TCP/21

Command to start an FTP server on Linux:
```
sudo systemctl start vsftpd
```
Command to connect to an FTP server:
```
ftp <server-ip>
```

2. SSH (Secure Shell) – TCP/22

Command to connect to a remote server via SSH:
```
ssh username@<server-ip>
```
Generate SSH keys:
```
ssh-keygen -t rsa -b 4096
```

3. Telnet – TCP/23

Command to test connectivity to a port using Telnet:
```
telnet <server-ip> <port>
```

4. SMTP (Simple Mail Transfer Protocol) – TCP/25

Test SMTP server using Telnet:
```
telnet <smtp-server> 25
```

5. DNS (Domain Name System) – UDP/TCP/53

Query DNS using dig:
```
dig example.com
```
Flush DNS cache on Windows:
```
ipconfig /flushdns
```

6. DHCP Server – UDP/67

Restart DHCP service on Linux:
```
sudo systemctl restart isc-dhcp-server
```

7. DHCP Client – UDP/68

Release and renew IP address on Windows:
```
ipconfig /release
ipconfig /renew
```

What Undercode Say:

Understanding and managing network ports is fundamental for IT and cybersecurity professionals. By mastering these ports, you can ensure secure and efficient network operations. Practice the commands and steps provided to strengthen your skills in network administration and security. For further reading, check out resources like Cisco’s Guide to Network Ports or NIST’s Cybersecurity Framework.