If you are hosting your web applications on Managed/Shared Server, then you don’t have to worry about it.
However, for VPS or dedicated you must consider doing all it takes to secure your server.
Having unwanted ports opened is a bad idea and attacker can take advantage of it in many ways.
Here are online FREE tools, which will help you to find out what all ports are opened so you can review and block them if not needed.
Note: if you’re running a port scan on your website DNS and if that is behind the proxy like Cloud Flare or SUCURI then it may not give you the accurate information.
You must use the actual server IP.
Liste of Port Scanner
Port Scan by MX ToolBox
MX Toolbox attempt to test 15 common ports with a timeout of 3 seconds and give you the results whether it’s opened or filtered.
TCP Port Scan with Nmap
Pentest Tools check opened ports using NMAP on the targeted host. You can choose to detect OS, service version.
It will give you the results of opened port and option to save the scan details in PDF format.
Online Port Scanner
This tool is a personal project of Javier Yanez, available to use in free to scan the ports against IPV4 or IPV6 address.
Port Scan by T1 Shopper
Scan the individual or range ports listening on server IP. This is useful if you just want to scan the targeted ports.
Port Scanner by Hacker Target
Perform a quick scan with most common six ports (FTP, SSH, SMTP, HTTP, HTTPS, RDP) with hosted NMAP port scanner.
Scan for around 1000 frequently used ports with NMAP or specify the custom ports against your domain or IP.
Port Scanner by DNS Tools
Quickly scan for some of the standard ports like FTP, SMTP, DNS, Finger, POP3, SFTP, RPC, IRC, IMAP, VNC, etc.
I hope above tools help to find the opened ports on your domain or IP. You may use a firewall to allow the ports you need and configure to deny all.