Port 3331: Unassigned — Quietly Claimed by Oracle Key Manager

What Port 3331 Is

Port 3331 is unassigned. The Internet Assigned Numbers Authority (IANA) maintains the official registry of port-to-service mappings, and 3331 has no entry.¹ No vendor has filed a claim. No RFC governs it.

That doesn't mean it's unused.

The Range It Lives In

Port 3331 sits in the registered port range (1024–49151). This range exists as a middle ground between the well-known ports (0–1023), which are tightly controlled and require elevated privileges to open, and the ephemeral ports (49152–65535), which operating systems hand out temporarily for outbound connections.

Registered ports are available to any software vendor or developer who formally registers with IANA. The idea is orderly coexistence: pick a number, file the paperwork, and everyone knows what lives where. Some vendors skip the paperwork.

What Actually Uses Port 3331

Oracle Key Manager uses port 3331 for its OKM CA (Certificate Authority) service, without an official IANA registration.² Oracle Key Manager is enterprise storage encryption infrastructure — it manages the encryption keys that protect data on tape drives and storage arrays in large data centers.

The port appears in three traffic patterns within an OKM cluster:

• Manager to KMA: The management console connects to Key Management Appliances on port 3331
• Agent to KMA: Tape drives and storage agents authenticate to KMAs on port 3331
• KMA to KMA: Appliances in a cluster communicate with each other on port 3331

Its neighbors tell the story: port 3332 handles certificates, 3333 handles management, 3334 handles agents, 3335 handles discovery, 3336 handles replication. Oracle quietly planted a cluster of ports here.

Security note: Port 3331 has historically appeared in trojan horse port lists. No specific, currently active malware family is prominently associated with it today, but its unassigned status makes it an attractive choice for software that wants to blend in. If you see unexpected traffic on 3331 and you're not running Oracle Key Manager, that's worth investigating.

How to Check What's Listening on Port 3331

On Linux or macOS:

# Show the process listening on port 3331
ss -tlnp | grep 3331

# Or with lsof
lsof -i :3331

On Windows:

# Show listening ports with process IDs
netstat -ano | findstr :3331

# Then look up the PID
tasklist /fi "pid eq <PID>"

Why Unassigned Ports Matter

The port registry only works when people use it. When vendors deploy on unregistered ports, conflicts become possible — two applications assuming they own the same number. The registered range has over 48,000 slots. There's no good reason not to file the paperwork.

Port 3331's story is a small illustration of how the Internet actually works versus how it was designed to work: governance by convention, not enforcement. IANA can list a port as unassigned, but it can't stop Oracle from using it.