Port 315 sits in the well-known ports range (0-1023), officially assigned by IANA to a protocol called DPSI. It's documented. It's reserved. And it's almost invisible.
What Port 315 Is Assigned To
According to IANA, port 315 is assigned to DPSI (Distributed Process System Interface) on both TCP and UDP.1 DPSI is described as a protocol that enables communication and data sharing between distributed processes within a network—a way for applications on different systems to talk to each other.2
That's what the registry says. But here's the honest truth: there's almost no documentation about DPSI's origins, no specification to read, no RFC to study, and very little evidence of it being used in modern networks.
The Well-Known Ports Range
Port 315 belongs to the System Ports (also called Well-Known Ports), which span from 0 to 1023.3 These ports are assigned by IANA through formal procedures—"IETF Review" or "IESG Approval"—and are meant to be reserved for services that matter enough to occupy this privileged space.
Getting a well-known port isn't trivial. You need documentation, a real use case, and formal approval. Port 315 was assigned to DPSI through this process, which means someone, somewhere, thought this protocol was important enough to reserve it.
The Mystery
Here's what we don't know about DPSI:
- Who created it
- When it was created
- What organization developed it
- Whether it was ever widely deployed
- If anyone still uses it today
The protocol appears in firewall signatures and network security tools,4 suggesting it's recognized by the infrastructure that watches network traffic. But finding actual software that uses port 315 for DPSI? That's another story.
Why This Matters
Port 315 represents something important about how the Internet maintains its infrastructure: we keep records of things that may no longer exist in practice.
The IANA registry is careful. It doesn't delete assignments lightly. Port 315 remains reserved for DPSI, even if DPSI itself has faded into obscurity or was never widely adopted. This creates a kind of archaeological record—a list of protocols that were planned, implemented, or hoped for, but didn't necessarily survive into the present.
It's honest bookkeeping. Better to reserve the port and keep it documented than to let it become a free-for-all where conflicting services might claim the same number.
Checking What's Actually Listening
If you want to see what's actually using port 315 on your system:
On Linux or macOS:
On Windows:
Chances are, you'll find nothing. Port 315 is registered, but rarely occupied.
The Bigger Picture
The Internet's port system includes thousands of assignments like this—protocols registered decades ago, services that sounded important at the time, standards that never quite became standard.
Port 315 is a reminder that the Internet is built on layers of history. Some layers are active, carrying billions of packets every second. Others are quiet, their purpose forgotten or fulfilled long ago.
This port exists. It's documented. It's reserved. But whether anyone is actually using it for DPSI? That's an open question.
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