Port 420 is officially assigned to SMPTE (Society of Motion Picture and Television Engineers) for both TCP and UDP.1 It sits in the well-known ports range (0-1023), which means IANA allocated it for a specific purpose. But here's the strange part: nobody seems to be using it.
What Is SMPTE?
The Society of Motion Picture and Television Engineers is the organization that builds the standards for how video moves across networks.2 Every broadcast you watch, every streaming platform you use, every frame that travels from camera to screen—SMPTE probably wrote the specification for how that happens.
SMPTE ST 2110, their modern standard for professional media over IP networks, uses RTP (Real-time Transport Protocol) over UDP.3 It doesn't use port 420. The organization has moved on.
The Well-Known Ports Range
Ports 0-1023 are the well-known ports, assigned by IANA for system-level services.4 These are the ports that require root privileges to bind on Unix systems. They're supposed to be important. They're supposed to be used.
Port 420 has the official assignment. It has the IANA registration. But it appears to be a placeholder, a reserved seat at a table where nobody sits.
Security Note
Port 420 has been associated with malware activity in the past.5 Trojans have used this port for command and control communications, likely because it's assigned but rarely monitored. An empty port is an opportunity.
If you see unexpected traffic on port 420, investigate it. Legitimate SMPTE traffic on this port is rare enough that any activity should raise questions.
How to Check What's Listening
On Linux or macOS:
On Windows:
If something is listening on port 420 and you don't recognize it, find out what it is.
Why This Port Matters
Port 420 represents something important about the port system: official assignments don't guarantee usage. IANA can designate a port, an organization can register it, and then the world can move on without it.
The well-known ports range is finite. There are only 1,024 of them. Port 420 is taking up space that could potentially be used for something else, but port number reclamation is rare. Once assigned, ports tend to stay assigned, even when nobody's home.
The Modern Reality
Modern SMPTE protocols like ST 2110 use dynamically negotiated ports for RTP streams, not a fixed well-known port.3 The video broadcasting industry moved to managed IP networks with sophisticated session negotiation. They don't need port 420 anymore.
But the port remains registered. An artifact. A placeholder. The empty chair at the table.
Frequently Asked Questions
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