Port 3611: Six Degrees — A Name Without a Network

What Port 3611 Is

Port 3611 sits in the registered ports range (1024-49151) — the space where applications claim a number by asking IANA to record their name alongside it. It's a voluntary registry, not a technical lock, but it's how the Internet tries to prevent two different applications from stepping on each other.

According to the IANA Service Name and Transport Protocol Port Number Registry, port 3611 is assigned to "six-degrees" — registered by Zach Nies in September 2002 for both TCP and UDP.¹

The Story Behind the Name

September 2002 was an interesting moment. Friendster launched in 2003. MySpace in 2003. Facebook in 2004. Someone in 2002 was building a social networking application — something about connecting people through the mathematical idea that any two humans are separated by at most six steps of acquaintance — and they registered a port for it.

The application never became notable enough to leave a documentation trail. No RFC was filed. No protocol specification survives in searchable form. The port number is still in the registry, but the software it was reserved for has no presence on the modern Internet.

It's a fossil. Proof that someone was thinking about social graphs and peer-to-peer human connection before those ideas had obvious names.

What You're Likely Seeing

If port 3611 appears in your logs or firewall output, it is almost certainly not the Six Degrees application from 2002. More likely candidates:

• A custom internal application that picked a port without checking the registry
• Scanning traffic probing for open ports (automated scanners cover wide ranges)
• A misconfigured or obscure third-party tool

There is no modern, widely-distributed software known to use port 3611 by default.

How to Check What's Listening

On Linux or macOS:

# Show what process is listening on port 3611
ss -tlnp | grep 3611

# Or with lsof
lsof -i :3611

On Windows:

# Find the process ID listening on port 3611
netstat -ano | findstr :3611

# Then look up the PID in Task Manager, or:
tasklist /FI "PID eq <PID>"

If nothing appears, nothing is listening. The port is available and quiet.

Why Registered Ports Matter

The registered range exists so applications don't have to guess. When you write software that communicates over a network, you register a port so other software knows where to find you, and so routers and firewalls can make informed decisions about traffic.

The system only works if people actually consult the registry. Most don't. Ports in the registered range are routinely claimed by applications that never checked — and equally routinely ignored by applications that did. Port 3611 is a small monument to the gap between the tidy registry and the chaotic reality of software in the wild.