Port 3256: Compaq RPM Agent — A Registered Port in Quiet Retirement

What Port 3256 Is

Port 3256 is a registered port — the middle tier of the port number hierarchy, spanning 1024 through 49151. Registered ports are claimed with IANA for specific purposes, distinguishing them from the well-known ports below 1024 (which carry the Internet's core protocols) and the ephemeral ports above 49151 (which OSes hand out dynamically for outgoing connections).

IANA records port 3256 as assigned to cpqrpm-agent — the Compaq Remote Program Monitor agent — on both TCP and UDP.¹

The Compaq RPM Agent

RPM (Remote Program Monitor) was part of Compaq's server management stack, the kind of out-of-band monitoring infrastructure that large enterprises relied on to keep track of hardware health across server fleets. When HP acquired Compaq in 2002, these tools were absorbed into HP's own management portfolio and eventually deprecated.

The protocol never had significant documentation outside of Compaq's internal systems. Today, it has no meaningful deployment footprint. You will not encounter this service in the wild unless you are running very old HP/Compaq server infrastructure — and even then, it is unlikely to be listening on this port.

The W32.HLLW.Dax Footnote

In 2002, a worm called W32.HLLW.Dax targeted Windows systems with remote access capabilities and used port 3256 as part of its communication.² It is a historical artifact — a piece of malware written for the exact era when Compaq was still a company. Modern antivirus signatures catch it instantly. It is not a current threat.

It is worth noting: port 3256 appearing in traffic is almost always more interesting as an anomaly than as an expected service.

How to Check What's Listening on This Port

If you see port 3256 active on a system and want to know what's using it:

On Linux or macOS:

sudo ss -tlnp | grep 3256
# or
sudo lsof -i :3256

On Windows:

netstat -ano | findstr :3256
# Then look up the PID:
tasklist | findstr <PID>

If something is listening on 3256 and you don't recognize it, treat that as worth investigating. The legitimate use case for this port is narrow, old, and rare.

Why Unassigned-Adjacent Ports Matter

Port 3256 illustrates something true about the registered port range generally: most of it is sparsely used legacy territory. IANA has assigned hundreds of ports to services that no longer exist, or to vendor-specific protocols that never saw broad adoption. The registered range is a graveyard of 1990s and early 2000s enterprise software.

That matters for security. An attacker looking to run a service on a port that won't trigger immediate suspicion often reaches for obscure registered ports. A port that "should" have a legitimate owner but has no active deployment in your environment is a reasonable place to hide something.

Monitor what's listening. Unused registered ports are not inherently dangerous, but unexpected activity on them is worth a second look.