Port 1584: Unassigned — Claimed by Squid Proxies

Port 1584 sits in the registered port range (1024-49151) but has no official service assigned by IANA. Despite this, it's been claimed through common use by Squid proxy cache servers.

What Lives Here

Squid Proxy Cache is the most common resident of port 1584. Squid is a widely-deployed web caching and proxy application that helps speed up web browsing by storing frequently-accessed content. When Squid needs to communicate between web servers and proxy servers, port 1584 is often where that conversation happens.¹

This wasn't officially blessed by IANA. Squid just started using it, and the practice stuck.

The Registered Range

Port 1584 belongs to the registered ports range (1024-49151). These ports can be registered with IANA for specific services, but registration isn't mandatory. Anyone can use them, which is both a feature and a problem.

This range exists between the well-known ports (0-1023) that require root privileges and the ephemeral ports (49152-65535) that operating systems assign randomly. It's the middle ground where most network applications live.

Why Unassigned Ports Matter

Not every port needs an owner. The Internet has 65,535 ports per protocol (TCP and UDP), and most of them sit empty, waiting. Unassigned ports serve as:

• Space for experimentation — Developers can test new protocols without paperwork
• Flexibility — Applications can grab a port number without waiting for IANA approval
• Room to grow — The Internet needs space for services that don't exist yet

But this flexibility creates ambiguity. Port 1584 might be running Squid on one server and something entirely different on another. There's no guarantee.

Security Considerations

Any port can be misused, but unassigned ports carry extra risk because there's no standard for what should be running on them. If you see traffic on port 1584, you need to verify what's actually using it.

To check what's listening on port 1584:

# On Linux/macOS
sudo lsof -i :1584
sudo netstat -tulpn | grep 1584

# On Windows
netstat -ano | findstr :1584

If you're not running Squid and you see activity on this port, investigate. It could be legitimate software that chose this port arbitrarily, or it could be something you don't want on your network.

How This Port Gets Used

TCP port 1584 uses the Transmission Control Protocol, which guarantees ordered, reliable delivery. This matches Squid's needs—proxy communications require reliability.

UDP port 1584 can also be used with the User Datagram Protocol, though this is less common for Squid. UDP trades reliability for speed, which doesn't fit most proxy use cases.

Related Ports

Other ports commonly associated with web proxies and caching:

• Port 3128 — Squid's default HTTP proxy port
• Port 8080 — Common alternative HTTP proxy port
• Port 8443 — HTTPS proxy alternative