Port 250: Unassigned — The Empty Chair in the Well-Known Range

Port 250 is nobody's door.

It sits in the well-known ports range (0-1023), the most carefully controlled addresses in the Internet's numbering system. These are the ports that require IETF Review or IESG Approval to assign. The ports where SMTP lives (25), where SSH answers (22), where HTTPS flows (443).

And port 250? Empty. Unassigned. Waiting.

What "Unassigned" Means

The Internet Assigned Numbers Authority (IANA) maintains the official registry of port assignments. According to RFC 6335, ports exist in three states:

• Assigned — A protocol owns this door
• Reserved — IANA is holding this for special purposes (or it was once assigned and returned)
• Unassigned — Available for assignment if someone asks

Port 250 is unassigned. It has never been claimed. When RFC 6335 was written, approximately 76% of well-known ports were assigned.¹ Port 250 is part of the remaining 24%.

The Well-Known Range

Ports 0-1023 are called system ports or well-known ports. On most operating systems, only root processes can bind to them. They're the foundation layer—the ports where essential Internet services are expected to live.²

Getting a well-known port assigned requires proving that ports from the User range (1024-49151) and Dynamic range (49152-65535) are unsuitable. The bar is high. The approval process is strict.

Yet port 250 remains unclaimed. Not because someone tried and failed, but because nobody tried.

What Might Be Listening

Since port 250 has no official assignment, what runs on it depends entirely on the local system. Some possibilities:

• Custom application someone configured to use port 250
• Testing or development service running on a non-standard port
• Nothing at all (most common)

Port scanners sometimes report port 250 as "unassigned" or "unknown." That's accurate. There is no protocol you should expect to find there.

How to Check What's Listening

On Unix-like systems (Linux, macOS):

# See what's listening on port 250
sudo lsof -i :250

# Or using netstat
sudo netstat -tuln | grep :250

# Or using ss (modern replacement for netstat)
sudo ss -tuln | grep :250

On Windows:

# See what's listening on port 250
netstat -ano | findstr :250

If nothing returns, nothing is listening. That's the expected state for port 250.

Why Unassigned Ports Matter

Unassigned ports are the gaps in the addressing system. They're reminders that not every number needs a purpose. The Internet has 65,535 ports per protocol (TCP and UDP). Many will never be assigned.

Port 250 sits in the most coveted range—the well-known ports—and remains empty. It's a pocket of silence in the most carefully controlled namespace on the Internet.

Someone could request it tomorrow. IANA could assign it next year. Or it could remain unassigned forever.

For now, port 250 is an empty chair at a crowded table. Reserved for something important enough to justify occupying well-known space, but that something hasn't arrived yet.