Port 1552: pciarray — A registered port that never found its purpose

Port 1552 is officially registered with IANA under the service name "pciarray" for both TCP and UDP.¹ And that's about all anyone can tell you with certainty.

What We Know (and Don't Know)

Status: Registered port (range 1024-49151)
Official name: pciarray
Protocols: TCP and UDP
What it does: Unknown

The IANA registry lists port 1552, but there's no RFC, no public documentation, and no widespread evidence of active use. The name suggests some connection to PCI (Peripheral Component Interconnect) arrays—possibly a protocol for managing or monitoring PCI devices over a network—but that's speculation.²

This port exists in the registry the same way a reserved parking spot exists: someone claimed it, but the car never showed up.

The Registered Port Range

Port 1552 lives in the registered port range (1024-49151). Unlike well-known ports (0-1023) which require IETF standards, registered ports can be claimed by anyone with a legitimate use case. You submit an application to IANA, provide a service name and description, and if approved, the port is yours.³

The problem: there's no requirement to actually use it. No mandate to publish documentation. No enforcement that the service ever launches.

So the registry fills with ports like 1552—names without services, reservations without occupants.

Why This Matters

Unassigned and obscure ports aren't just bureaucratic trivia. They matter because:

Security risk: Malware and trojans love obscure ports. If legitimate traffic rarely uses port 1552, malicious traffic can hide there more easily. Security databases have flagged port 1552 as associated with trojan activity in the past—not because pciarray is malicious, but because the port's obscurity made it attractive to attackers.⁴

Network monitoring: Administrators seeing traffic on port 1552 can't quickly determine if it's legitimate. Well-known ports are self-documenting. Obscure registered ports require investigation.

The namespace isn't infinite: There are only 65,535 possible ports. Thousands of them are registered to services that never materialized. Every ghost port like 1552 is one less port available for protocols that might actually need it.

How to Check What's Using Port 1552

If you see traffic on port 1552 or want to verify what's listening:

On Linux/Mac:

# See what's listening on port 1552
sudo lsof -i :1552

# Or using netstat
netstat -an | grep 1552

On Windows:

# Check listening ports
netstat -an | findstr 1552

# See which process is using it
netstat -aon | findstr 1552

If something is listening on port 1552, it's either:

• A rare implementation of the pciarray protocol (unlikely)
• A custom application that chose this port arbitrarily
• Malware using the port's obscurity as cover

The Port Registry's Ghosts

Port 1552 isn't unique. The IANA registry is full of ports like this—officially registered, technically claimed, practically invisible. They're the abandoned buildings of the Internet's addressing system: structures that exist on the map but serve no current purpose.

Some were registered with genuine intent that never materialized. Others were claimed defensively, holding space for a protocol that never launched. A few were used briefly in the 1990s and then forgotten as the services died.

They remain in the registry because port numbers, once assigned, are rarely reclaimed. The namespace slowly fills with ghosts.