Port 20009 has no official assignment from the Internet Assigned Numbers Authority (IANA). It sits in the registered port range (1024-49151), which exists specifically so that applications can register stable port numbers and avoid conflicts. And yet, this port remains unassigned.1
That hasn't stopped anyone from using it.
What the Registered Range Means
Ports 1024-49151 are called registered ports. Unlike well-known ports (0-1023), which require root privileges to bind and carry foundational Internet protocols, registered ports are available for any application that wants a stable, globally recognized port number.2
The idea is simple: if you're building software that needs a specific port, you register it with IANA. They review your request, check for conflicts, and grant you a number. Now your application has a home that won't collide with someone else's software.3
Port 20009 is registered with IANA in the sense that it exists in the registered range. But nobody has formally claimed it. The registry shows no assignment, no protocol, no official owner.
Unofficial Use: Parallels Remote Application Server
In practice, port 20009 is used by Parallels Remote Application Server (RAS) for Client Manager gateway communication. Specifically:4
- TCP/UDP 20009: Used between the Publishing Agent and the Gateway when Client Manager is enabled
- Clients connect through a router or firewall on port 20009, which forwards to the RAS Gateway server
- The related product 2X RAS Terminal also uses UDP 20009 for the same purpose
This is not a small application. Parallels RAS is enterprise software for remote desktop infrastructure. It's used in corporate environments, deployed across networks, configured in firewalls. And it runs on an unregistered port.
Why This Happens
There are 48,128 ports in the registered range. IANA has assigned a fraction of them. The rest sit empty, waiting for someone to file the paperwork.
But filing the paperwork takes time. It requires documentation, technical review, IETF or IESG approval depending on the process.3 It's easier to pick an unused number and ship your software.
The risk is collision. If two applications independently choose port 20009, they'll conflict when installed on the same system. But in practice, the registered range is so large and so sparsely populated that conflicts are rare. Most applications pick a number, check that it's not widely used, and move on.
This creates an informal secondary system: thousands of unassigned ports in active use, documented only in vendor knowledge bases and firewall configuration guides.
How to Check What's Listening
If you need to know what's using port 20009 on your system:
Linux/macOS:
Windows:
These commands show active connections and listening services on the port. If nothing appears, the port is unused on your system.
Why Unassigned Ports Matter
Port 20009 represents a choice in Internet architecture. The registered port range exists to create order, to prevent chaos, to ensure that applications don't step on each other.
But order requires participation. It requires developers to register their ports, to follow the process, to believe that coordination matters more than convenience.
Most of the registered range remains unassigned. Not because there aren't enough applications to fill it, but because the informal system works well enough that the formal system feels optional.
Port 20009 is unassigned. But it's not unused. It's evidence that the Internet runs on a mix of official architecture and unofficial agreement, and somehow, that's been enough.
Related Ports
- 20008: Also unassigned, numerically adjacent
- 20010: Also unassigned, numerically adjacent
- 1024-49151: The full registered port range
Frequently Asked Questions
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