Port 242 is officially assigned to a service called "direct" — a database replication protocol developed by PeerDirect in the mid-1990s. This is a well-known port, part of the privileged 0-1023 range managed by IANA. But here's the thing: only TCP on port 242 was ever used. UDP was assigned by convention, then left empty.1
This is a ghost port. Officially registered, technically reserved, but quietly abandoned.
What the Direct Protocol Did
The "direct" service was the network transport layer for PeerDirect's database replication engine (PDRE). From 1995 to 2001, PeerDirect built systems software for distributed databases — technology that let different database systems sync data across networks, resolve conflicts, and maintain consistency.2
This was infrastructure work. Not flashy, but essential. Before cloud-native databases and automatic replication, someone had to build the pipes.
Herb Sutter, PeerDirect's CTO, designed the replication engine. He's better known now as chair of the ISO C++ standards committee and author of books like Exceptional C++. But before teaching the world how to write better code, he was solving the problem of how to make databases in different cities stay synchronized.3
Port 242 was the door those databases used to talk.
Why UDP Was Never Used
When you register a port with IANA, you typically claim both TCP and UDP even if you only plan to use one. It's a reservation — keeping both protocols clear in case you need them later.
PeerDirect never needed UDP. Database replication demands reliability: every transaction, every conflict resolution, every sync operation needs guaranteed delivery. That's TCP's job. UDP is fast and lightweight, but it doesn't promise your data will arrive or arrive in order.1
So UDP on port 242 just sat there. Registered but unused. Free for anyone to claim, but nobody did.
The Port Range: Well-Known Ports (0-1023)
Port 242 sits in the well-known ports range — ports 0 through 1023. These are the system ports, the privileged assignments. On Unix-like systems, only root can bind to these ports. They're reserved for foundational services: HTTP on 80, HTTPS on 443, SSH on 22.
Getting a well-known port in the 1990s meant your protocol was serious. IANA doesn't hand these out casually. PeerDirect's "direct" service earned its spot because database replication was critical infrastructure for enterprises building distributed systems.
But unlike HTTP or SSH, "direct" never became ubiquitous. The port was assigned, the protocol was real, but the service faded as PeerDirect's technology either got absorbed into other systems or eclipsed by newer approaches to database replication.
What Happened to PeerDirect
PeerDirect operated through the late 1990s and into the early 2000s. Herb Sutter left in 2001 and joined Microsoft in 2002, where he spent 22 years working on C++ and influencing how millions of developers write code.23
The "direct" protocol didn't survive PeerDirect's decline. Modern database replication uses different approaches: streaming replication, log shipping, change data capture. The problem PeerDirect solved still exists, but the solutions evolved.
Port 242 remains registered to "direct," but the service behind it is gone.
Security Considerations
Because port 242 is barely used, it's occasionally exploited by malware looking for unmonitored ports. Some Trojans have used port 242 for command-and-control communication, precisely because it's assigned but rarely watched.4
If you see traffic on port 242 and you're not running legacy PeerDirect software (which almost nobody is), investigate. It shouldn't be active.
How to Check What's Listening
On Linux or macOS:
On Windows:
If something is listening and you don't recognize it, find out what it is. Port 242 should be quiet.
Why This Port Matters
Port 242 is a monument to infrastructure work that mattered briefly, then faded. It represents the unglamorous reality of the Internet: most protocols don't become HTTP or DNS. They solve a problem, serve a purpose, and then get replaced by something better or just quietly stop being used.
The port remains assigned because IANA doesn't reclaim registrations casually. Removing an assignment risks breaking legacy systems that might still depend on it somewhere. So port 242 stays registered to "direct," a name that tells you almost nothing unless you know the story.
Herb Sutter built something real here. A system that let databases stay synchronized across networks in an era when that was hard. The protocol is gone, but the port remains — a breadcrumb in the IANA registry, a footnote in the history of distributed systems.
Port 242 is a ghost port. Officially claimed. Technically reserved. Quietly forgotten.
Related Ports
- Port 118 (SQL Services) — Another early database-related port assignment
- Port 156 (SQL Service) — SQL network protocol
- Port 3306 (MySQL) — Modern database protocol in the registered ports range
- Port 5432 (PostgreSQL) — Another modern database system
Frequently Asked Questions
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