Port 3595 — Unassigned

What Range This Port Belongs To

Port 3595 is a registered port — part of the range from 1024 to 49151 that IANA maintains as a public registry. Unlike the well-known ports below 1024 (which require root privileges on Unix systems and carry decades of history), registered ports are available to any application developer who files a request with IANA.

IANA lists port 3595 as unassigned for both TCP and UDP.¹ No application has claimed it. No RFC defines it. No standard says what should run here.

Any Known Unofficial Uses

Nothing notable. Port 3595 doesn't appear in threat intelligence databases as a common malware channel, isn't associated with a popular application that chose it informally, and has no documented history of widespread use.

One distraction worth clearing up: the Cisco SNS-3595 is a physical server appliance whose model number happens to be 3595. It doesn't use port 3595. The model number and the port number are unrelated.²

How to Check What's Listening on This Port

If you're seeing traffic on port 3595 on your system, it's something local to your environment. To find out what:

On Linux or macOS:

sudo ss -tlnp | grep 3595
# or
sudo lsof -i :3595

On Windows:

netstat -ano | findstr :3595
# Then look up the PID:
tasklist | findstr <PID>

The process name will tell you what claimed the port. It's almost certainly a legitimate application that needed a port and picked this one — or your OS assigned it dynamically as an ephemeral port before the proper ephemeral range starts at 49152.

Why Unassigned Ports Matter

The registered port range contains roughly 48,000 slots. Most are empty. This emptiness isn't wasted space — it's the buffer that lets new protocols find a home, lets applications stake out territory without trampling each other, and lets the port system scale as new services emerge.

The assignment process is intentionally low-friction. A developer submits a request, IANA reviews it, and a port gets reserved. The cost of not doing this is coordination chaos: two unrelated applications claiming the same port, firewalls blocking legitimate traffic because a port became associated with malware, protocols that can't be deployed because their preferred port was already taken informally by something else.

Port 3595's empty status means the Internet hasn't needed it yet. Or the application that uses it never bothered to register.