Check Open Ports on Windows

What open ports are

An open port is a TCP or UDP port that a program is using to accept traffic. There are 65,535 of them in three ranges:

1. Well-known ports (0-1023) for common services such as FTP (21), SSH (22) and HTTP (80).
2. Registered ports (1024-49151) assigned to products and vendors.
3. Dynamic ports (49152-65535) for short, private connections.

Why check

• Malware can use open ports to talk to its controller.
• A port that is open by mistake can let attackers in.
• Needless services use system resources.
• A port clash is a common cause of "app will not start" problems.

netstat

Open Command Prompt and run:

netstat -an

Look in the Local Address column. The number after the colon is the port. LISTENING means the port waits for connections.

To see which program uses the port, add -ob in an Administrator prompt:

netstat -ano

The last column is the process ID. Match it in Task Manager under Details.

PowerShell

Open PowerShell and run:

Get-NetTCPConnection -State Listen

The column LocalPort shows the port and OwningProcess the process ID.

Nmap

Nmap is a free port scanner.

1. Download and install it from the official Nmap site.

   

2. Open Command Prompt and scan your own machine:

nmap localhost

Add -p 1-65535 to check all ports.

Close a port you do not need

Stop the program or service that uses it. Or block the port in Windows Defender Firewall with an inbound rule.

Quick recap

• netstat -ano and Get-NetTCPConnection show listening ports.
• Match the process ID in Task Manager.
• Close ports you do not need.