Port 236 has never been assigned to any service. It's not unassigned in the sense of "available for anyone to request." It's reserved—held back by IANA for nearly four decades.
What Reserved Means
The Internet Assigned Numbers Authority (IANA) manages port numbers in three states:
- Assigned — Currently allocated to a specific service
- Unassigned — Available for assignment upon request
- Reserved — Not available for regular assignment; held for special purposes1
Port 236 falls into that third category. It's part of a block (ports 225-241) that was marked "Reserved" in RFC 1060 back in 1986 and remains that way today.2
The Well-Known Port Range
Port 236 sits in the System Ports range (0-1023), also called Well-Known Ports. These are the ports that require IETF Review or IESG Approval to assign—the most carefully guarded range in the port number space.3
This range contains the essential protocols of the Internet: HTTP (80), HTTPS (443), DNS (53), SSH (22), SMTP (25). Ports here are for protocols that matter, protocols that will be around for decades.
Why Reserve Ports?
Reserved ports exist as breathing room. They're held at the edges of ranges or in specific blocks to allow the port number system to expand or adapt in the future. Port 236's block (225-241) sits in a transitional zone—after the densely-packed lower ports and before the more sparsely-assigned higher ranges.
RFC 6335 notes that reserved values may be used "to extend these ranges or the overall port number space in the future."1 Port 236 is potential energy—a placeholder for a protocol that doesn't exist yet but might need to.
No Unofficial Uses
Unlike some unassigned ports that get picked up by applications looking for an unused number, port 236 shows no widespread unofficial usage. It's quiet. Truly unused. If something's listening here on your system, it's either a mistake or something very unusual.
How to Check What's on Port 236
On Linux and Unix systems, you can check if anything is listening on port 236:
Using ss (modern, recommended):
Using netstat (deprecated but still common):
Using lsof (shows all open files and network connections):
On Windows:
If nothing's listening, you'll see no output. That's the expected state for port 236.4
The 38-Year Question
Port 236 has been reserved since 1986. The World Wide Web didn't exist yet. The Internet had maybe 5,000 connected hosts. The entire ARPANET was smaller than a single modern data center.
And here's port 236, still reserved, still waiting.
Why? We don't know. IANA doesn't publish the reasoning behind specific reservations. Maybe this block was held for protocols that were being discussed but never materialized. Maybe it's structural—a buffer zone in the port number space. Maybe it's just bureaucratic inertia.
Whatever the reason, port 236 sits empty. A door with no room behind it. A number in the registry with nothing attached.
Related Ports
Port 236 sits in the middle of the reserved block:
- Port 224 — masqdialer (assigned)
- Ports 225-241 — Reserved block (including 236)
- Port 242 — direct (assigned)
The reserved block is surrounded by assigned services, but the block itself remains untouched.
Frequently Asked Questions
The Honest Truth
Port 236 is a placeholder. A port number with no purpose. It's been sitting in the registry for 38 years, never used, never assigned, quietly reserved.
There's something oddly beautiful about that. The Internet is built on protocols and services that flow through specific ports, carrying the traffic of billions of people. And here's port 236—silent, empty, waiting for a protocol important enough to break the seal on this reserved range.
Maybe that protocol will come. Maybe it won't. Either way, port 236 will be here, holding space in the registry, a door that's never been opened.
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