Port Scan for Mac

$ brew install nmap
$ nmap -sV example.com

What it’s for

Every network service listens on a numbered port: websites on 443, SSH on 22. Port Scan tries a range of ports on a host and reports which ones accept a connection. Scan only hosts you own or have permission to test.

Use it when

• You set up a server and want to see what it exposes.
• A service doesn’t work, and you want to know whether its port is open at all.
• You want to check that a firewall blocks what it should.

Reading the result

The summary beside the table counts each state and lists the open ports.

What you might see

• Everything filtered, on a device in your home. macOS may be blocking the scan. Netutilus needs Local Network access, in System Settings › Privacy & Security › Local Network. A hint appears when this looks likely.
• Every UDP port Open|Filtered. Normal for a host on the internet: many networks suppress the replies that would show a port closed. A note under the summary says so.
• An open port you didn’t expect. See what the Software column says, then stop that service or block the port.

Options worth knowing

• Ports takes ranges and lists, such as 22,80,443,8000-8100.
• Detect services reads what each open port says about itself, after the scan.
• Also UDP probes ten common UDP services, each with a request in its own protocol.
• Right-click an open port to open it in your browser, or to check its certificate in SSL Certificate.

Related

• Ports, what they are.
• LAN Scanner finds the devices on your network, and checks the services of each.