Port 3483: SlimProto — The Squeezebox's Knock

What This Port Does

Port 3483 sits in the registered port range (1024–49151). These ports are administered by IANA, which maintains an official registry of assigned services. Port 3483 currently has no formal IANA assignment — but it has a well-documented life anyway.

For roughly two decades, port 3483 belonged to the Squeezebox ecosystem. It served two roles simultaneously, split by protocol:

• UDP 3483 — The Slim Devices Discovery Protocol. When a Squeezebox player powers on, it broadcasts a UDP packet asking the local network "is there a media server here?" The server, if present, replies. No manual configuration needed.
• TCP 3483 — The SlimProto protocol. Once a player finds its server, it opens a persistent TCP connection on this port. From that point forward, all playback control flows through it: play, pause, skip, volume, status updates, stream handshakes.¹

The same port number, two transports, two jobs. Discovery over UDP, then control over TCP.

The Squeezebox Ecosystem

Slim Devices was a California company that built networked music players starting around 2001 — years before Sonos, years before AirPlay. Their first product, the SliMP3, streamed MP3s over a wired network. Their software, originally called SlimServer and later Squeezebox Server, ran on a home computer and served music to the players.

Logitech acquired Slim Devices in 2006, rebranded the hardware as Squeezebox, and discontinued the product line in 2012. But the server software survived — it was open-sourced and continued as Logitech Media Server, then handed off to the community as Lyrion Music Server, which still maintains it today.²

The SlimProto protocol never got an RFC. It was developed in-house, documented on the project wiki, and implemented by a devoted community of audio enthusiasts. Port 3483 was simply the port they chose — and it stuck.

Who Still Uses This Port

More people than you'd expect. The Squeezebox hardware is discontinued but not dead. Thousands of players still run on home networks. And Squeezelite — a software player that implements SlimProto — keeps the protocol alive on any machine that can run it.³ Home Assistant has a native SlimProto integration.⁴

If you see port 3483 open on a home network, someone is probably running Lyrion Music Server (or its predecessors) and playing music through it.

What Range This Port Belongs To

Registered ports (1024–49151) require IANA registration, but enforcement is limited. Any application can bind to any port — the registry is a coordination mechanism, not an access control list. The result: ports accumulate unofficial uses, especially in the home networking and media streaming space, where open-source software picks ports informally and the names stick through community convention rather than official process.

Port 3483 is a clean example of this. The IANA registry shows it unassigned. The rest of the world knows it as Squeezebox.

How to Check What's Listening on This Port

On macOS or Linux:

# Check if anything is bound to port 3483
lsof -i :3483

# Or using ss (Linux)
ss -tulnp | grep 3483

On Windows:

netstat -ano | findstr :3483

If you see Lyrion Music Server (or its predecessors — "squeezebox server", "logitechmediaserver") in the results, that's expected. If you see something unexpected, that's worth investigating.