Port 3541: VoiSpeed — A Registered Port the Internet Forgot

What Port 3541 Is

Port 3541 sits in the registered ports range (1024–49151). IANA assigned it in July 2002 to VoiSpeed, a VoIP PBX (Private Branch Exchange) software product from an Italian company. The port serves as the web management interface for VOIspeed servers — administrators reach the control panel by browsing to http://[server-ip]:3541/services.cgi.

So this port is not technically unassigned. It is claimed. It just happens to be claimed by software most people have never heard of.

What VOIspeed Is

VOIspeed is a SIP-based PBX platform, primarily deployed in Italian businesses. Like most PBX systems, it needs a management interface reachable over the network. Port 3541 is that interface — TCP for web access, UDP for remote login sessions. ¹

It is not widely deployed globally, which is why nearly every port database describes port 3541 as "unassigned" or "unknown." The IANA registration exists. The product exists. The overlap with the broader Internet is minimal.

What the Registered Ports Range Means

The registered ports range (1024–49151) requires an application with IANA for assignment. The process is supposed to prevent two different applications from unknowingly claiming the same port. In practice:

• Registrations are often filed and then abandoned as products evolve
• Many products use ports without ever registering them
• Many registered ports become orphans when companies fold or protocols change

Port 3541 is a mild example of this: registered, actively used by one product, essentially invisible to the rest of the Internet.

How to Check What Is Listening on This Port

If you see activity on port 3541 and you are not running VOIspeed, something else is using it. Check with:

# Linux/macOS
sudo ss -tlnp | grep 3541
sudo lsof -i :3541

# Windows
netstat -ano | findstr :3541

The output will show the process ID. Cross-reference with your process list to identify what opened the port.

Should You Be Concerned?

If port 3541 is open on a machine and you did not deliberately configure VOIspeed or another application to use it, investigate. Any open port is a potential attack surface. An unexpected listener on an obscure registered port warrants a look.