Port 10226 — Unassigned, Claimed by Azure

The Port Range

Port 10226 exists in the registered ports range (1024–49151), defined by RFC 6335 and managed by IANA. These are the ports anyone can request an official assignment for. They don't require superuser privileges. Most will never be officially assigned. Many are used anyway. ¹

The Unofficial Use

Port 10226 is used by StackExchange.Redis, a popular .NET client library for Redis, when connecting to Azure Redis Cache instances. The library reserves a range: ports 10221–10231. These are cluster communication ports in Azure's Redis implementation. If your Azure Redis Cache scales up and your VNET firewall hasn't explicitly allowed this range, connections fail. ²

Users don't pick 10226. The library does. The port became real because Microsoft designed it that way.

How to Check

Check what's listening on port 10226:

Linux:

netstat -pan | grep 10226
lsof -i :10226

Windows:

netstat -bano | findstr 10226

macOS:

lsof -i :10226

Why This Matters

The registered port range exists to prevent chaos: without structure, every program would pick random numbers and collide. But structure creates empty spaces. Port 10226 is structurally valid and available—ready to be assigned if someone applies to IANA, or ready to be used unofficially if the need is immediate enough.

Azure didn't ask permission. They needed the range, their client library needed it, and they used it. The system accommodates both: official assignments and pragmatic reality.

This is how the Internet actually works: between the lines of specification, in the space between governance and necessity.