Port 784 lives in the well-known ports range (0-1023), the space managed by the Internet Assigned Numbers Authority (IANA) for standardized services. But unlike its neighbors, port 784 has no official assignment. The registry lists it as unassigned—available, waiting, unused by any permanent protocol.
Except it wasn't always unused.
The Experimental Years
In 2021 and 2022, port 784 UDP had a purpose. The early drafts of DNS-over-QUIC (DoQ)—a protocol designed to encrypt DNS queries using the QUIC transport protocol—specified port 784 for experimentation.12
Researchers scanned the IPv4 address space looking for DoQ resolvers on port 784, testing whether this new approach to DNS privacy could work at scale.3 Engineers ran servers on 784, clients connected to it, and for a brief period, this unassigned port carried the future of encrypted DNS.
Then the working group moved on. Draft-02 of the DNS-over-QUIC specification shifted experimentation to port 8853, and the final standard (RFC 9250) settled on port 853—already assigned to DNS-over-TLS since 2016.4
Port 784 was left behind.
What This Port Represents
Port 784 sits in the well-known range because that space was created when the Internet was smaller and IANA could reasonably assign every important service a number below 1024. These ports require root/administrator privileges to bind on Unix-like systems—a security measure from a different era.
Being unassigned doesn't mean unused. Developers use unassigned ports for testing all the time. A port number is just a 16-bit integer that lets multiple services share the same IP address. If you're running a temporary service and need a port, you can pick any number that isn't already in use on your system.
Port 784 is one of many such numbers—officially unclaimed, occasionally borrowed, always available.
Why Unassigned Ports Matter
The Internet has 65,535 ports per protocol (TCP and UDP). IANA manages assignments for 0-49151. The rest are ephemeral—your computer assigns them randomly when you open a connection.
Unassigned ports in the well-known range are increasingly rare. There's ongoing discussion about whether IANA should stop assigning new well-known ports entirely, since modern operating systems and containerization have reduced the need for globally standardized port numbers.5
Port 784 represents the space between—not important enough for permanent assignment, but available when someone needs to try something new.
Checking What's Listening
If you want to see whether anything is using port 784 on your system:
On Linux or macOS:
On Windows:
If nothing returns, the port is available. If something appears, you'll see the process ID and name of whatever claimed it.
The Honest Truth
Port 784 is unassigned. It has no official protocol, no RFC defining its purpose, no permanent home in the infrastructure of the Internet.
But for a while, it mattered. Engineers used it to test whether DNS could be faster and more private. They ran experiments, collected data, and moved on when they found a better port number.
That's how the Internet evolves. Not every experiment needs a permanent address. Sometimes a port is just a place to try something—and that's enough.
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