Port 10022 — The Unassigned Port Where SSH Goes When It Gets Blocked

What Port 10022 Is

Port 10022 is unassigned. The Internet Assigned Numbers Authority (IANA) has not officially designated a service for this port. It exists in the registered port range (1024-49151)—the middle tier of TCP/UDP ports reserved for applications, not system services. ¹

This distinction matters. Ports below 1024 (0-1023) require administrative privileges to use. Ports above 49151 are dynamic and ephemeral—they're what your operating system hands out to temporary connections. The registered range is democratic territory. Your application can claim it if no one else has, and port 10022 is a port that nobody officially owns.

Where It Actually Lives

In practice, port 10022 is almost exclusively used as an alternative SSH port. ²³ The reason is simple: Port 22, the standard SSH port, is frequently blocked.

ISPs block it to reduce automated attacks on their own infrastructure. Corporate firewalls block it because they don't want their employees SSHing out to random servers. Hosting providers sometimes block it to prevent abuse. When port 22 is inaccessible, system administrators reach for 10022—not because there's a rule saying to, but because it's high enough to require admin privileges, well-documented enough to be recognized, and low enough to not conflict with ephemeral ranges. It's a pragmatic consensus that emerged from necessity.

You'll also see 10022 configured for SFTP servers (SSH File Transfer Protocol)—a file transfer service built on top of SSH that depends on port 22 by default and similarly rotates to 10022 when needed. ⁴

How to Check What's On It

You can check if anything is listening on port 10022 on your system:

On macOS or Linux:

# Check if anything is listening
lsof -i :10022

# Or with netstat:
netstat -an | grep 10022

# Or with ss (modern systems):
ss -tlnp | grep 10022

On Windows:

netstat -ano | findstr :10022

To check a remote server:

# From the Internet—often blocked if firewall is active
nc -zv example.com 10022

# Or with nmap (if you have it):
nmap -p 10022 example.com

If you see a connection, check what service is actually using it:

# On your own machine, see the process
lsof -i :10022

Why Unassigned Ports Matter

The port numbering system has roughly 65,000 addresses (0-65535). Only a few hundred are officially assigned—there aren't enough official assignments for the hundreds of thousands of applications that need network access. Unassigned ports like 10022 are the escape valve.

They're where innovation happens without waiting for bureaucracy. They're where workarounds become standards. Port 10022 exists because someone needed SSH on an unusual port, and the system said "sure, that's available, use it." Millions of SSH tunnels now flow through it. No RFC defined it. No committee assigned it. The Internet simply absorbed it into the fabric of how it actually works.

This is the difference between specification and practice. On paper, port 10022 means nothing. In reality, administrators worldwide know exactly what it is. The system's flexibility—its willingness to let you use any unassigned port—is part of why the Internet can adapt without breaking.