Port 3688: simple-push-s — A Name Without a Living Protocol

What Port 3688 Is

Port 3688 sits in the registered ports range (1024–49151). These ports are not assigned by IANA the way well-known ports below 1024 are, but they are registered — meaning someone filed a request, IANA reviewed it, and the port number was set aside for a named purpose.

For port 3688, that named purpose is simple-push-s: the secure variant of the simple-push protocol, registered in January 2003 by C. Enrique Ortiz.¹ Its sibling, plain simple-push (unencrypted), lives on port 3687.

What simple-push Was

In 2003, push notifications were an unsolved problem. Mobile devices were beginning to matter. Someone wanted a lightweight, standardized way to push messages to them over a network. simple-push was an attempt at that.

The protocol never became widely adopted. No major software ecosystem built on it. No RFC was published to define it formally. The registration in the IANA registry is essentially the only artifact that remains. The Internet moved on and invented push notifications several other times, better.²

This makes port 3688 something specific: a ghost port. It has an official name. It has no living occupant.

What's Actually on Port 3688 Today

Because the original protocol never deployed, nothing meaningful is standardized on this port. In practice, any software can use it — and some do. If you see traffic on port 3688, it is almost certainly an application that chose the port for its own reasons, not an implementation of simple-push-s.

To find out what's listening on port 3688 on your own machine:

macOS / Linux:

# Show what process is listening on port 3688
lsof -i :3688

# Or with ss (Linux):
ss -tlnp | grep 3688

Windows:

netstat -ano | findstr :3688
# Then look up the PID in Task Manager, or:
tasklist | findstr <PID>

If nothing is returned, nothing is listening. That's the normal state for this port on most machines.

Why Ghost Ports Matter

The registered port space contains thousands of entries like this — protocols that seemed like good ideas in 2003 (or 1995, or 2010) and then quietly faded. They occupy a slot in the registry but no meaningful slice of the actual Internet.

This isn't waste. The registry's purpose is partly historical: it records what was attempted, prevents accidental collisions, and gives network administrators a reference point when they see unexpected traffic. A port with a registered name is easier to investigate than pure mystery.

Port 3688 is quiet. If you see it active in a network scan, you now know: whatever is there did not inherit the name.