Port 560 sits in the well-known ports range (0-1023), officially assigned to rmonitor (remote monitor daemon). It's a number that exists more in registries than in actual networks—a reserved address for a protocol the Internet largely forgot.
What rmonitor Was
The rmonitor protocol was designed for lightweight remote system monitoring. The idea was simple: a monitoring client would send queries to remote hosts over port 560, and those hosts would respond with status data—system load, uptime, service availability.1
It used UDP for speed, operating on a request-response pattern. Quick checks, minimal overhead, no connection management. For its time, it made sense.
What Range Port 560 Belongs To
Port 560 is in the well-known ports range (0-1023), also called system ports. These are assigned by IANA and historically required root/administrator privileges to bind to. They're reserved for standard network services—or at least services that were standard when they were assigned.2
The well-known range is where protocols go to live forever, whether they're still used or not.
Why You Don't See It Anymore
The world moved on. Modern monitoring systems like Nagios, Prometheus, Zabbix, and countless cloud-based solutions do what rmonitor did, but better. They offer encryption, authentication, detailed metrics, alerting, visualization—everything rmonitor couldn't provide.
UDP port 560 might technically be listening somewhere, but it's not what administrators reach for when they need to monitor systems. The protocol exists in the registry, but not really in practice.
How to Check What's Listening
If you're curious whether anything is actually using port 560 on your system:
On Linux/macOS:
On Windows:
Most of the time, you'll find nothing. Port 560 is assigned, but silent.
Why Unassigned—Or Unused—Ports Matter
The IANA port registry isn't just a list of what's currently popular. It's a permanent record of assignments. Once a port is assigned to a service, that assignment tends to stick, even if the service fades into obscurity.
This matters because:
- Conflict avoidance: Even obsolete assignments prevent new services from claiming the same number and causing confusion
- Historical compatibility: Ancient systems might still expect rmonitor on 560—rare, but possible
- Registry integrity: The system works because assignments are stable and predictable
Port 560 holds its place not because rmonitor is thriving, but because the Internet remembers. Numbers, once assigned, are harder to take back than to leave reserved.
The Honest Truth
Port 560 is a ghost. Officially assigned, rarely used, quietly persistent. It's a reminder that the Internet's infrastructure carries the weight of its history—protocols that mattered once, numbers that still belong to them, and the long tail of obsolescence that never quite disappears.
If you see port 560 listening on a modern system, you're either looking at something very old, or something pretending to be.
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