Port 437: comscm — The Ghost in the Registry

Port 437 sits in the well-known port range (0-1023), officially assigned by IANA to a service called "comscm"—Communication Server Control Message. Both TCP and UDP. Contact: Jim Teague.¹

That's where the story ends. Or rather, where it never really began.

The Protocol That Left No Trail

Search for comscm. Search for Jim Teague. Search for Communication Server Control Message. You'll find almost nothing. No RFC defining the protocol. No documentation explaining what it does. No historical record of what problem it solved or what systems used it.

Just a name in the IANA registry, assigned decades ago, with no explanation.

This is genuinely strange. Most well-known ports have RFCs, documentation, mailing list discussions—some kind of paper trail. Port 437 has none of that. It's a registered address with almost no one home.

The Second Life: Network Quality Analyzers

Years later, network equipment vendors started using port 437 for something else entirely: Network Quality Analyzer (NQA) tools.² These are monitoring applications that watch network performance in real-time—bandwidth usage, latency, packet loss. They talk to routers and switches, usually over SNMP, and use port 437 for their control communications.

Whether this is related to the original "comscm" protocol or just vendors repurposing an obscure assigned port is unclear. The connection between Communication Server Control Message and network quality analysis isn't obvious, but it's plausible they're related—both involve servers and control messages.

What This Port Teaches Us

Port 437 is a reminder that the Internet's nervous system has dark corners. Not every port has a rich story. Not every protocol left documentation. Some assignments were made in the early days, when the Internet was smaller and less formal, and the reasons are lost to time.

The well-known port range (0-1023) is supposed to be the prestigious neighborhood—ports assigned by IANA for important, well-documented services. Port 437 got a spot on that block, but almost no one remembers why.

Security Considerations

Because port 437 is obscure and poorly documented, it's sometimes flagged by security tools as suspicious. Some malware has used it opportunistically—precisely because it's not commonly monitored.³

If you see traffic on port 437:

• Check if you're running network monitoring tools (NQA, similar applications)
• If not, investigate what's listening
• Restrict access with firewalls or ACLs
• Use authentication (SSH, HTTPS) if the service requires external access

How to Check What's Using Port 437

Linux/macOS:

sudo lsof -i :437
sudo netstat -tulpn | grep :437

Windows:

netstat -ano | findstr :437

If something's listening and you don't recognize it, investigate.

Related Ports

• Port 161/162 (SNMP): Network monitoring and management (what NQA tools often use alongside 437)
• Port 514 (Syslog): System logging, another network monitoring protocol
• Port 199 (SMUX): SNMP Unix Multiplexer, related to network management