Port 606 is officially assigned to the Cray Unified Resource Manager (URM)—a service that managed computing resources on Cray supercomputers running the UNICOS operating system.12
Unless you work with legacy Cray systems, you will almost certainly never encounter traffic on this port.
What Is the Cray Unified Resource Manager?
The Unified Resource Manager was part of Cray Research's infrastructure for managing supercomputer resources—scheduling jobs, allocating processors, managing memory across massive parallel systems.3
This was infrastructure for machines that cost millions of dollars, filled entire rooms, and required liquid cooling. The kind of computers where people submitted batch jobs and waited. Where computational time was measured in billing units. Where "resource management" meant something very different than spinning up a container.
Port 606 was assigned in the well-known port range (0-1023), which tells you something about when this service was created. IANA doesn't hand out well-known ports anymore except in rare cases. Port 606 comes from an era when you could still get a two or three-digit port number for your specialized protocol.
Why This Port Still Exists
Port 606 remains officially assigned because IANA doesn't typically revoke port assignments. The registry is append-only. Once a port is claimed, it stays claimed—even if the service that used it has been extinct for decades.
This creates ghost ports. Addresses that still technically belong to software that barely runs anymore.
What Range This Port Belongs To
Port 606 is in the well-known port range (0-1023). These ports are assigned by IANA for standardized services. They require root or administrator privileges to bind to on most operating systems—a security measure to prevent unprivileged programs from impersonating system services.
Most well-known ports were assigned in the 1980s and 1990s, during the era when the Internet was smaller and you could still maintain a canonical list of every important network service.
How to Check What's Listening on Port 606
On Linux or macOS:
Or using netstat:
On Windows:
If you find something listening on port 606, it's either:
- An actual legacy Cray system (unlikely unless you work in a national lab or supercomputing center)
- Software that repurposed the port for something else
- Malware (port 606 has been used by trojans in the past, precisely because it's usually unmonitored)4
Why Unassigned and Obscure Ports Matter
The port registry contains thousands of assignments like this—services that made sense in 1985, protocols for hardware that no longer exists, software that died with the companies that made it.
These ports still matter because:
They create security blind spots. Nobody monitors port 606. If malware uses it, it might go unnoticed longer than traffic on port 80 or 443.
They represent history. Every assigned port is a bookmark in the history of networking. Port 606 marks the era when supercomputers were rare, expensive, and required their own specialized resource management protocols.
They're technically still reserved. You shouldn't use port 606 for your own service, even though the thing it was assigned to barely exists anymore. The Internet runs on conventions, and "don't squat on assigned ports" is one of them.
The Honest Reality
You will never need to configure port 606. You will never need to open it in your firewall. You will never see legitimate traffic on it unless you maintain a museum of computing history.
But it's still there in the registry, a small monument to the machines that came before cloud computing, before distributed systems fit in Docker containers, back when "resource management" meant something you needed a dedicated protocol for.
Port 606 is a ghost. And the Internet is full of them.
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