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Understanding critical network ports is essential for maintaining secure and efficient IT infrastructure. Below are some of the most important ports and their functions:
1️⃣ FTP (File Transfer Protocol) – TCP/21
📂 Purpose: Facilitates file transfers between clients and servers.
2️⃣ SSH (Secure Shell) – TCP/22
🔒 Purpose: Provides a secure, encrypted channel for remote login and command execution.
3️⃣ Telnet – TCP/23
🖥️ Purpose: Enables remote login and command execution, but lacks encryption, making it less secure.
4️⃣ SMTP (Simple Mail Transfer Protocol) – TCP/25
📧 Purpose: Handles email transmission between clients and mail servers, as well as between mail servers.
5️⃣ DNS (Domain Name System) – UDP/TCP/53
🌐 Purpose: Resolves human-readable domain names into IP addresses and vice versa.
6️⃣ DHCP Server – UDP/67
📡 Purpose: Assigns IP addresses and network configuration parameters to DHCP clients.
7️⃣ DHCP Client – UDP/68
📲 Purpose: Allows client machines to obtain IP address leases and network settings from a DHCP server.
You Should Know:
1. FTP (TCP/21)
FTP is widely used for transferring files between systems. However, it is not secure by default. Use SFTP (SSH File Transfer Protocol) for encrypted file transfers.
– Command to start FTP server on Linux:
sudo systemctl start vsftpd
– Command to connect to an FTP server:
ftp <server-ip>
2. SSH (TCP/22)
SSH is the go-to protocol for secure remote access. Always disable root login and use key-based authentication for better security.
– Command to generate SSH keys:
ssh-keygen -t rsa -b 4096
– Command to copy SSH key to a remote server:
ssh-copy-id user@remote-server
3. Telnet (TCP/23)
Telnet is outdated and insecure. Replace it with SSH wherever possible.
– Command to test a port using Telnet:
telnet <server-ip> <port>
4. SMTP (TCP/25)
SMTP is used for sending emails. Ensure your SMTP server is properly configured to prevent email spoofing.
– Command to test SMTP server:
telnet <smtp-server> 25
5. DNS (UDP/TCP 53)
DNS is critical for resolving domain names. Use tools like `dig` or `nslookup` to troubleshoot DNS issues.
– Command to query DNS records:
dig example.com
– Command to flush DNS cache on Windows:
ipconfig /flushdns
6. DHCP Server (UDP/67) and Client (UDP/68)
DHCP automates IP address assignment. Ensure your DHCP server is secure to prevent rogue DHCP attacks.
– Command to release and renew DHCP lease on Windows:
ipconfig /release ipconfig /renew
– Command to restart DHCP service on Linux:
sudo systemctl restart isc-dhcp-server
What Undercode Say:
Understanding and managing network ports is crucial for IT professionals. Always prioritize security by disabling unused ports, using encrypted protocols, and regularly auditing your network configurations. Tools like `nmap` can help you scan and monitor open ports:
nmap -p 1-1000 <target-ip>
For Windows, use the `netstat` command to check active connections:
netstat -an
Additionally, consider implementing firewalls (e.g., `iptables` on Linux or Windows Firewall) to restrict access to critical ports.
### **Expected Output:**
- Secure your network by disabling Telnet and using SSH.
- Regularly audit open ports using tools like `nmap` or
netstat. - Use encrypted protocols like SFTP and HTTPS whenever possible.
- Monitor DHCP and DNS configurations to prevent unauthorized access.
By following these steps, you can ensure a secure and efficient IT infrastructure.
References:
Reported By: Shaifali Shaifali – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
