Port 3180: mc-brk-srv — A Reserved Port for a Protocol That Never Arrived

What Port 3180 Is

Port 3180 sits in the registered ports range (1024–49151) — the middle tier of the port number space, where IANA assigns identifiers to specific services through a formal process. Registered ports aren't reserved exclusively like well-known ports, but they carry an official designation that represents someone's intent.

Port 3180's official name is mc-brk-srv — Millicent Broker Server.

Almost no one has heard of it.

The Protocol That Claimed It

In 1995, researchers at Digital Equipment Corporation's Systems Research Center in Palo Alto published a paper about a protocol called Millicent.¹ The team — Steve Glassman, Mark Manasse, Martín Abadi, Paul Gauthier, and Patrick Sobalvarro — had identified a real problem: every payment system of the era cost several cents per transaction, which made it economically impossible to charge someone a fraction of a cent for anything.

Their solution was scrip: vendor-specific digital cash that could be validated locally, without a centralized server, without expensive cryptography, and at very low overhead. A broker (running on port 3180) would act as an intermediary — you'd buy scrip from the broker, and spend it directly with vendors. The vendor validated it locally. No per-transaction bank call. No credit card fees. Purchases as small as a tenth of a cent were theoretically viable.

The vision was a web where you paid small amounts for small things. A fraction of a cent to read one article. A penny to watch a short video. Microtransactions not as an abstract concept, but as a working infrastructure.

Steve Glassman registered the port with IANA.²

What Happened

Millicent never shipped at scale. The prototype worked — the team demonstrated around 1,000 Millicent requests per second — but adoption never followed. The web took a different path: free content supported by advertising, then subscriptions, then paywalls. The overhead of getting users to hold scrip from every broker, and vendors to integrate a novel payment protocol, was too high.

By the early 2000s, Millicent was a research artifact. DEC itself was acquired by Compaq in 1998, then Compaq by HP in 2002.

The port remains registered in the IANA table. Nothing meaningful listens on it.

What Range This Port Belongs To

Port 3180 is a registered port (1024–49151). These ports:

• Require an application to IANA for assignment
• Are not elevated — most operating systems don't require special privileges to bind them
• Are often used by commercial and legacy applications that predate the modern Internet

The registered range is large enough to contain both active workhorses and historical relics. Port 3180 is firmly in the latter category.

Checking What's on This Port

If you see traffic on port 3180, it's not Millicent. Something else is using it — either an application that picked the port deliberately, or one that grabbed it dynamically. To check:

Linux / macOS:

# Show what's listening on port 3180
ss -tlnp sport = :3180

# Or with lsof
lsof -i :3180

Windows:

netstat -ano | findstr :3180

If you find a process ID, cross-reference it with Task Manager or tasklist to identify the application.

Why Unoccupied Registered Ports Matter

The registered port range contains thousands of ports assigned to protocols that faded, companies that folded, or ideas that didn't spread. They're not dangerous — they're just unused. But they matter as evidence of the Internet's history: every registered port represents a moment when someone believed strongly enough in a protocol to formalize it.

Port 3180 marks the moment someone thought the web was going to run on micropayments.