Port 1017 — Unassigned Well-Known Port

What This Port Is

Port 1017 belongs to the well-known port range (0-1023), where IANA reserves numbers for standardized, system-critical services that form the backbone of Internet communication. Port 22 is SSH. Port 80 is HTTP. Port 443 is HTTPS. But 1017 is not assigned to anything official. ¹

The Gap

Every well-known port is either assigned (to a service documented in the IANA registry) or unassigned (reserved but awaiting formal assignment). Port 1017 is unassigned. It sits in a locked cabinet with the label removed. This matters because software developers know: these ports are sacred. Don't use them without permission. ²

What Actually Uses It

On macOS and some Unix systems, RPC services (Remote Procedure Call) sometimes claim port 1017 for network communication. Specifically, NetInfo, the directory service used in older versions of Mac OS X, relied on RPC and would use available unassigned ports including 1017. Portmap, the RPC registry service, may also direct traffic here. ³

But this is not official. No RFC defines port 1017. No standard says NetInfo must use it. It just happens to be available when the system looks for a port to use.

How to Check What's Using It

To see if anything is listening on port 1017:

# On macOS/Linux:
sudo lsof -i :1017

# Or using netstat:
netstat -tuln | grep 1017

# Check RPC services specifically:
rpcinfo -p localhost

If you see traffic on port 1017, it's almost certainly an RPC service or legacy macOS component. It won't be something you installed intentionally.

Why Unassigned Ports Matter

This is the port system's paradox: IANA reserves the well-known range to prevent chaos, yet services still need ports. So they use the unassigned ones. Port 1017 represents a small piece of that necessary chaos—a space held in reserve that gets borrowed when needed, without ever becoming official.

The well-known range exists to create order. Unassigned ports like 1017 prove that perfect order is impossible. And that's exactly why they exist.