What This Port Is
Port 3542 is registered with IANA as hacl-monitor, short for High Availability Cluster Monitor. The registration dates to July 2002, during the era when HP-UX clusters dominated enterprise Unix computing.
The service was designed to monitor the health of nodes in an HA cluster — systems where two or more servers mirror each other so that if one fails, another takes over automatically. The monitor component would check whether cluster members were alive and responding, coordinating with other hacl-* services on nearby ports (5300 for heartbeat, 5301 for general services, 5302 for configuration).
Both TCP and UDP are listed for this port in the IANA registry.1
Why You Probably Won't See It
The hacl family of ports was tied to HP's proprietary clustering stack, primarily used on HP-UX. That ecosystem has largely been retired in favor of Linux-based HA solutions like Pacemaker, Corosync, and cloud-native redundancy. If you scan a modern network and find traffic on port 3542, it is almost certainly not hacl-monitor.
This is the gap between registered and deployed. IANA registrations don't expire. A port can be claimed in 2002 for software that's no longer widely installed and stay registered indefinitely. Port 3542 is a quiet corner of the registry — technically occupied, practically vacant.
What Range This Port Belongs To
Port 3542 sits in the registered ports range (1024–49151). This range is managed by IANA and intended for services that have formally applied for an assignment. Unlike the well-known ports below 1024, registered ports don't require elevated privileges to bind on most operating systems — any process can listen here.
The practical implication: if you find something listening on 3542 on your system, it's not hacl-monitor from 2002. It's whatever software decided to use this port, registered assignment notwithstanding.
How to Check What's Listening
To see if anything is using port 3542 on your machine:
Linux / macOS:
Windows:
If these commands return nothing, the port is idle. If something appears, the process name or PID will tell you what claimed it.
האם דף זה היה מועיל?