Port 537 sits in the well-known ports range with an official IANA assignment, but it tells a story about the gap between registry names and deployed reality.
What Runs on Port 537
Port 537 is assigned to NMSP (Networked Media Streaming Protocol).1 But if you encounter traffic on this port in the wild, you're almost certainly seeing something else: Cisco's Network Mobility Services Protocol—a proprietary system for managing wireless networks.
The two protocols share an acronym but serve completely different purposes.
The Cisco Reality
In practice, NMSP on port 537 is Cisco's Network Mobility Services Protocol—the communication channel between their Mobility Services Engine (MSE) and Wireless LAN Controllers (WLC).2
What it does:
- Tracks the location of wireless devices across enterprise networks
- Manages context-aware services (knowing where clients are and what they're doing)
- Handles wireless intrusion prevention system (wIPS) data
- Supports hyperlocation features for precise device positioning
- Exchanges probe data and RSSI (signal strength) information
How it works: The protocol runs over TCP and uses TLS encryption.3 Wireless controllers connect to one or more Mobility Services Engines, sending bidirectional requests and responses about client locations, access point status, and network events.
This isn't a protocol you'll see on the public Internet. It lives inside enterprise wireless infrastructure—the invisible nervous system tracking devices as they roam between access points.
The Registry Mystery
The IANA registry lists port 537 as "Networked Media Streaming Protocol."1 This name suggests something designed to stream media content across networks—video, audio, real-time content delivery.
But there's no publicly documented RFC for such a protocol. No widespread deployment. No open standard. The registered name and the deployed reality don't match.
What likely happened: either the original protocol never gained traction and Cisco repurposed the port, or the registry name is a misunderstanding of what NMSP actually means in practice.
Security Considerations
If you're running Cisco wireless infrastructure:
- NMSP requires proper TLS configuration between controllers and MSEs
- The protocol carries sensitive location data about network clients
- Firewalls should restrict port 537 to trusted management networks only
- Misconfigured NMSP connections can expose wireless network topology
If you're not running Cisco equipment and see port 537 traffic, investigate—it's not a common protocol and shouldn't appear on general-purpose systems.
How to Check What's Using Port 537
On Linux/macOS:
On Windows:
Most systems won't have anything listening on port 537 unless you're running Cisco wireless management infrastructure.
The Well-Known Ports Range
Port 537 sits in the well-known ports range (0-1023), assigned and managed by IANA.4 These ports are reserved for system services and protocols that need consistent, recognized port numbers across the Internet.
Being in this range means port 537 was considered important enough to deserve a permanent assignment. But importance in the registry doesn't always translate to widespread use—and sometimes the protocol that gets deployed isn't the one the registry describes.
Why This Port Matters
Port 537 is a reminder that the port number system isn't just about technical specifications—it's about the gap between intention and reality.
The registry says one thing. The network does another. And somewhere in that gap is the actual work getting done: wireless controllers tracking devices, location services finding clients, enterprise networks managing mobility.
The name in the registry is "Networked Media Streaming Protocol." The traffic on the wire is Cisco tracking your phone as it moves between conference rooms. Both are NMSP. Neither is wrong. They're just different truths about the same number.
Frequently Asked Questions About Port 537
آیا دا پاڼه ګټوره وه؟