Port 3432: OSDCP — A Registered Ghost

What Port 3432 Is

Port 3432 sits in the registered ports range — numbers 1024 through 49151, managed by IANA. Unlike well-known ports (0–1023), registered ports don't require special OS privileges to open. Unlike ephemeral ports (49152–65535), they're meant to have stable, documented uses.

In theory, port 3432 has one: osdcp, listed in the IANA registry as "Secure Device Protocol," registered in March 2002.¹

In practice, this registration is a ghost.

The osdcp Registration

The IANA entry records the service name as osdcp, describes it as "Secure Device Protocol," and lists an individual registrant from 2002. Both TCP and UDP are assigned.

That's where the documentation ends. There's no published RFC for osdcp. No open-source implementation. No vendor documentation. No security research. The protocol may have been used in a private product that never shipped, or shipped and never gained traction, or quietly disappeared. Whatever it was, it left no footprint.

This is not unusual. The registered ports range contains hundreds of entries in the same condition — a name, a date, and silence.

What You Might Actually Find on Port 3432

If you see traffic on port 3432, it's almost certainly not osdcp. More likely candidates:

• Custom application ports — Developers sometimes pick ports in this range arbitrarily when they need a local service and want to avoid conflicts with common ports.
• Database instances — PostgreSQL's default port is 5432, and administrators running multiple instances sometimes use nearby numbers. Port 3432 occasionally appears in this context, though there's nothing official about it.
• Development tooling — Various local dev servers, proxies, and debugging tools use ports in the 3000–4000 range.

If you're seeing port 3432 open on a system you manage and you didn't put it there, that's worth investigating.

How to Check What's Listening

On Linux or macOS:

# Show which process has port 3432 open
ss -tlnp sport = :3432

# Or with lsof
lsof -i :3432

On Windows:

netstat -ano | findstr :3432

The process ID in the output will tell you what's actually using it.

Why Unassigned (and Vestigial) Ports Matter

The registered ports range exists so applications don't stomp on each other. If every developer picked port 8080, nothing would work. IANA registration is supposed to be a coordination mechanism — claim your port, publish your protocol, and other implementers know what they're building against.

When registrations go dark like osdcp did, they create small ambiguities. The port isn't free for others to register, but it's also not actively defended. In practice, nothing stops someone from running whatever they want on 3432 — IANA registration has no enforcement mechanism. It's a social contract, not a technical lock.

Most of the registered range works fine this way. A few hundred ghost entries are a small price for the coordination the system provides.