Port 803 sits in the well-known port range (0-1023) but has never been assigned an official service. It's been empty for decades.
What This Port Is
Port 803 is part of the well-known port range (ports 0-1023), which is controlled by IANA (Internet Assigned Numbers Authority). Ports in this range are supposed to be assigned to specific protocols and services that need universal recognition—things like HTTP on port 80 or SSH on port 22.
But not every number in this range has been claimed. Port 803 is one of the gaps.
The ports around it got assigned: port 800 runs MDBS daemon, port 802 carries Modbus Application Protocol Secure. But ports 803 through 809 remain unassigned.1
Unofficial Use: Mac OS X RPC Services
Port 803 occasionally appears in Mac OS X systems as part of RPC-based services. The range from 600-1023 has historically been used by macOS for services like NetInfo, though these are mostly for local use and not standardized across the Internet.2
This isn't an official assignment—just Apple using an available number for internal purposes.
Why Unassigned Ports Matter
The well-known port range isn't infinite. There are only 1024 numbers, and hundreds are already taken. The empty ones—like 803—represent future possibility. Maybe a new protocol will need a permanent home. Maybe not.
These gaps also serve as a reminder: not every door needs to be open. An unassigned port is just a number. It doesn't carry traffic, doesn't run a service, doesn't answer when knocked upon. It's there if needed.
Checking What's Using Port 803
Even though port 803 has no official assignment, something on your system might be using it. Here's how to check:
On Linux or macOS:
On Windows:
If nothing returns, the port is closed—which is what you'd expect for an unassigned port.
The Empty Spaces
The well-known port range is full of these gaps. Port 803 has been sitting empty while the Internet grew around it. The ports on either side carry real traffic, serve real purposes, connect real systems. Port 803 just waits.
Not every number needs a purpose. Sometimes the gaps are as important as what fills them.
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