What Port 3670 Is
Port 3670 sits in the registered port range — numbers 1024 through 49151 that IANA tracks on behalf of services, companies, and protocols that formally claimed them.
IANA's registry lists port 3670 as assigned to "smile" — described as a TCP/UDP interface, registered in 2003.1 Both TCP and UDP are listed.
That's essentially all the official record says.
The SMILE Protocol
No RFC was ever published for SMILE. No technical specification appears in any standards body's archive. The registration exists — you can find it in the IANA service names and port numbers registry — but it represents a protocol that never made it into public documentation, open-source implementations, or widespread use.
This isn't unusual. The registered port range has thousands of entries from companies that filed a port assignment for internal tools, proprietary systems, or products that were never widely deployed. IANA records the claim; the Internet doesn't have to care.
VideoReQuest, a legacy video-on-demand system, has also been documented using port 3670 in some network configurations — another low-profile use that never became standard.2
What This Means in Practice
If you see traffic on port 3670 on your network, it's almost certainly not SMILE. It's more likely:
- An application that picked the port arbitrarily
- A developer using it for a local service during testing
- Malware or unauthorized software — which sometimes gravitates toward registered-but-obscure ports because firewalls may leave them open
An unrecognized open port deserves investigation regardless of what IANA says lives there.
How to Check What's Listening
On Linux or macOS:
On Windows:
Match the PID from the output against Task Manager or Get-Process to identify the owning application.
Why Unassigned-in-Practice Ports Matter
The registered port range was designed to prevent collisions — two services shouldn't unknowingly claim the same port. But the registration system relies on voluntary compliance. Nothing technically stops an application from using port 3670 for something else entirely.
Ports like 3670 occupy a gray zone: officially claimed, functionally open. They're a reminder that the port registry is a coordination mechanism, not enforcement. The Internet runs on cooperation, and occasionally on benign neglect.
Related Ports
- 3669 — Unassigned
- 3671 — Unassigned
- 3389 — RDP (Remote Desktop Protocol), a heavily monitored neighbor in this general range
Frequently Asked Questions
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