Port 1509 was officially assigned to robcad-lm (Robcad License Manager), the licensing component for Robcad—a robotics simulation and automation software package that later became part of Siemens' Tecnomatix suite.1
What Robcad Was
Robcad was (and is, under Siemens) a workcell design and simulation tool. Engineers used it to virtually design, simulate, and validate automated manufacturing processes—spot welding robots, arc welding, laser cutting, painting systems, material handling. You could build a complete digital twin of a factory floor before installing a single robot.2
The kind of software where a single license cost tens of thousands of dollars.
The License Manager
Before cloud licensing and subscription models, enterprise software used dedicated license servers. When you launched Robcad, it checked port 1509 to verify:
- Did you actually pay for this seat?
- Are there available licenses?
- Is the license still valid?
No connection to port 1509? The software wouldn't run. IT departments maintained these license servers like infrastructure—because they were infrastructure.
What Port 1509 Carries (Or Carried)
Port 1509 operates over both TCP and UDP:
- TCP 1509: Connection-oriented license verification, where the client software establishes a persistent connection to verify licensing status
- UDP 1509: Connectionless license checks, typically for faster heartbeat-style verification
This is a registered port (1024-49151), meaning Robcad Ltd. formally requested this assignment from IANA for their license manager. It's not a well-known port like HTTP (80) or SSH (22), but it's officially documented.3
Current Status
Robcad still exists as part of Siemens Digital Industries Software. Whether modern versions still use port 1509 for licensing is unclear—most enterprise software has moved to cloud-based licensing systems that don't require dedicated ports.
The port registration remains, a artifact of how industrial software licensing worked in the 1990s and 2000s.
Security Note
Port 1509 has been historically associated with malware—trojans have used it to communicate.4 This doesn't mean the port itself is dangerous. It means malicious actors sometimes squat on registered ports because they're less likely to be blocked than random high ports. If you see unexpected traffic on 1509 and you're not running Robcad licensing software, investigate.
Checking Port 1509
To see if anything is listening on port 1509 on your system:
Linux/macOS:
Windows:
If something is listening and you're not running Robcad or Siemens Tecnomatix software, that's worth investigating.
Why Unassigned (and Assigned) Ports Matter
Port 1509 represents a specific era in enterprise software: before SaaS, before cloud licensing, when every major application had its own license server running on its own registered port. Network administrators had to open these ports. Firewalls had to allow them. License servers had to stay online or production stopped.
The registered port range (1024-49151) exists for exactly this purpose—giving applications stable, documented port assignments so they don't conflict with each other or with well-known services.
Most of these ports are quiet now. The software either moved to the cloud or disappeared entirely. But the registrations remain—a kind of archaeological record of what software once needed to function.
Related Ports
Other license manager ports in the registered range:
- Port 27000-27009: FlexNet Publisher (formerly FLEXlm), used by hundreds of CAD, engineering, and design applications
- Port 1947: Sentinel License Manager (formerly Sentinel RMS)
- Port 5093: Sentinel Keys Server
All serving the same purpose: verifying that the software running on your machine was actually paid for.
Frequently Asked Questions
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