Port 10515 — The Unassigned Door

What This Port Is

Port 10515 is an unassigned registered port. It doesn't appear in the IANA Service Name and Transport Protocol Port Number Registry—no RFC defined it, no standards body blessed it. Yet it exists, and things listen on it anyway. ¹

The Port Ranges Explained

The Internet divides ports into three worlds:

Well-known ports (0-1023): Reserved for the big players. HTTP, HTTPS, SSH, DNS—the foundation protocols. You need IANA approval to claim one here.

Registered ports (1024-49151): The middle ground. IANA maintains a registry of services here, but the registry is not exhaustive. This is where port 10515 lives—in the registered range, but never actually registered.

Dynamic/ephemeral ports (49152-65535): The free-for-all. Temporary ports that applications request on-the-fly. No one owns these.

Port 10515 occupies an interesting position: officially unclaimed, but practically used.

Observed Uses

Port 10515 appears most frequently in rsyslog configurations, the system logging daemon that runs on Linux and Unix machines. ² Rsyslog uses it as one of several UDP syslog input ports (alongside 10514 and 10516). Why this particular port? No official reason. It's simply chosen—a quiet place to listen for machine logs.

Organizations also use it for log aggregation and centralized syslog collection, particularly when integrating with tools like Logstash or Splunk. Since it carries no official mandate, teams are free to adopt it or ignore it without conflict. ³

How to Check What's Listening

If you suspect port 10515 is in use on your machine:

# Linux/macOS - see what's listening on 10515
sudo netstat -tlnp | grep 10515
# or with modern tools
sudo ss -tlnp | grep 10515

# See if a specific service is bound to it
sudo lsof -i :10515

On macOS specifically:

lsof -i :10515

If nothing is running, the port is silent. If rsyslog is there, you'll see it.

Why Unassigned Ports Matter

IANA could theoretically assign every port from 1024 to 49151. They don't. The unassigned ones are where the actual Internet lives—not the standardized protocols, but the particular choices organizations make for their particular problems.

When you see port 10515, you're not looking at a decision from a standards body. You're looking at a local choice that became convention. It's decentralized governance: the opposite of top-down design. No one has authority over port 10515, which means everyone has equal claim to it, which means the first to claim it wins by simple convention.

This is how the Internet actually works at the edges. The standards give you the structure. The unassigned ports give you the freedom.