Port 3123: EDIX — The Port That Got Reserved but Never Called

What Port 3123 Is

The IANA registry lists port 3123 as assigned to EDIX — an EDI Translation Protocol, registered for both TCP and UDP by William Randolph Roy. ¹

That's where the story stalls.

EDIX never became a real protocol in practice. It has no RFC, no open-source implementation, no documentation in common circulation. The assignment exists in the registry; the protocol does not meaningfully exist in the wild.

What EDI Actually Is

EDI — Electronic Data Interchange — is the standardized electronic exchange of business documents between companies: purchase orders, invoices, shipping notices, payment confirmations. ² The concept dates to the 1960s and today underpins an enormous share of global commerce. When a retailer's system automatically sends a purchase order to a supplier's system the moment inventory drops below threshold, and the supplier's system automatically confirms and schedules fulfillment — that's EDI.

It's unsexy infrastructure. It's also everywhere.

The two dominant EDI standards are ASC X12 (primarily North America, standardized 1979) and UN/EDIFACT (international, United Nations standard from 1987). Neither sends documents through port 3123. Modern EDI transmission runs over AS2, SFTP, OFTP, and HTTPS — standard transport protocols layered on top of the Internet's existing infrastructure.

Whatever EDIX intended to add to this landscape, it never added it.

The Registered Port Range

Port 3123 sits in the registered ports range: 1024 through 49151. ³

This range is where applications stake their claims. Unlike well-known ports (0-1023), which require IANA assignment and are reserved for established protocols like HTTP (80), SSH (22), and DNS (53), registered ports are open to any developer or organization willing to submit a request. IANA maintains the list, but usage is not strictly enforced. The result is a long registry of assignments — some thriving, some dormant, some like EDIX, where the name was registered but the protocol never shipped.

Security Notes

The SANS Internet Storm Center records regular scanning activity on port 3123. ⁴ This is typical of any registered port: automated scanners probe them looking for running services. Because EDIX never deployed, any active listener on port 3123 is almost certainly something else — an application that picked this port arbitrarily, a misconfiguration, or occasionally malware.

If you see unexpected activity on port 3123, investigate it. Don't assume it's harmless just because the official assignment is an obscure dormant protocol.

How to Check What's Listening

macOS / Linux:

lsof -i :3123

Windows:

netstat -aon | findstr :3123

Cross-platform (if netstat is available):

netstat -tulnp | grep 3123

These commands show you the process name and PID of anything bound to port 3123. If something is there, you'll know exactly what it is.

Related Ports

• Port 3122 — Unassigned
• Port 3124 — Unassigned
• Port 4000 / 4001 — Common ports for EDI gateway software