Port 3301: Unassigned — SAP's Quiet Squatter

What Port 3301 Is

Port 3301 has no officially assigned service. The Internet Assigned Numbers Authority (IANA) — the body that manages port assignments — lists it as unassigned in the registered ports range (1024-49151).¹

That range sits between the well-known ports (0-1023, reserved for foundational protocols like HTTP and SSH) and the ephemeral ports (49152-65535, used temporarily by client software). Registered ports are meant to be claimed by applications that register with IANA. Port 3301 never was.

The De Facto Use: SAP Gateways

In practice, port 3301 is associated with SAP enterprise software.

SAP uses a consistent port-numbering convention for its gateway services: ports 3300 through 3399, where the last two digits encode the system instance number. Port 3300 is the gateway for system instance 00. Port 3301 is sapgw01 — the gateway for system instance 01. Port 3302 is system instance 02, and so on.²

On Linux and UNIX systems running SAP, administrators are instructed to add this line to /etc/services:

sapgw01  3301/tcp  # SAP Gateway for system instance 01

This is not an IANA registration — it's a convention that SAP documents internally and propagates through its installation guides. Millions of enterprise deployments follow it. The port isn't officially SAP's, but in practice, if you see 3301 open on a corporate server, SAP is the overwhelmingly likely explanation.

Security Notes

Because port 3301 is unassigned, any service you find there is operating outside formal standards. In SAP environments, the gateway service running on this port handles RFC (Remote Function Call) connections — the protocol SAP uses for inter-system communication. Exposed SAP gateway ports have historically been targets for attackers looking to exploit RFC vulnerabilities, so they should be firewalled and not exposed to untrusted networks.³

Port scanners and security tools occasionally flag 3301 as anomalous simply because nothing is supposed to be there officially. In an SAP environment, that's expected. Elsewhere, it warrants investigation.

How to Check What's Listening

Linux/macOS:

# Show what process is using port 3301
ss -tlnp | grep 3301

# Or with lsof
lsof -i :3301

# Or with netstat
netstat -tlnp | grep 3301

Windows:

netstat -ano | findstr :3301

The process name or PID in the output will tell you what application claimed the port.

The Number 3301

There is one other famous 3301 on the Internet: Cicada 3301, the cryptographic mystery that began on 4chan in January 2012 and sent solvers hunting QR codes taped to lampposts in Paris, Seoul, Warsaw, and Miami — following a trail of prime numbers, steganography, and encrypted books written in runes.⁴

The two 3301s share nothing except the number. One is an unregistered network port used by enterprise software. The other is one of the strangest unsolved puzzles the Internet has ever produced. If you came here looking for the latter: wrong door.