Port 553 carries PIRP (Public Information Retrieval Protocol), a protocol designed in 1997 that tried to out-simple HTTP and lost. The port is officially assigned in the IANA registry, but the protocol it was meant to serve never found an audience.
What PIRP Was Trying to Do
In February 1997, D.J. Bernstein published an Internet draft proposing PIRP as "a simple, uniform, efficient, extensible, easily implemented method of publishing information."1 His critique was straightforward: FTP and HTTP were designed for file transfer and web browsing, not specifically for publication. PIRP would be different—dedicated, minimal, trivial to implement.
The protocol used TCP port 553 and operated through a simple request-response model. Clients would send structured names (encoded as netstrings), and servers would return the associated information. The entire specification fit in a few pages. Implementation was supposed to be "a small and trivial task."
It wasn't enough.
Why It Died
PIRP never progressed beyond experimental Internet drafts. The draft expired in August 1997, six months after it was published.2 There were multiple versions (00, 01, 02, and 05 are still archived), suggesting revisions and attempts to gain traction, but the IETF never endorsed it.
The timing was brutal. By 1997, HTTP had already won. The web was exploding. Browsers were everywhere. Developers had HTTP libraries, servers, and momentum. PIRP offered simplicity, but HTTP offered the entire ecosystem of the World Wide Web.
Simplicity doesn't matter if no one implements your protocol.
What Port 553 Carries Now
Effectively nothing.
Port 553 remains assigned to PIRP in the official registry, but the protocol is a ghost. You won't find PIRP servers running in the wild. You won't find modern software listening on port 553 for legitimate reasons.
Some security scanners flag port 553 for historical malware activity—trojans occasionally squat on obscure, unused ports because no one's watching them.3 But that's not about PIRP. That's about abandoned real estate.
Why Ghost Ports Matter
Port 553 is one of hundreds like it—officially assigned to protocols that sounded promising in Internet drafts but never escaped the 1990s. These ports are time capsules. They're evidence that protocol design is less about technical elegance and more about timing, momentum, and ecosystems.
PIRP might have been simpler than HTTP. It might have been more elegant. But HTTP had Netscape, Apache, and a million websites. PIRP had a text file on D.J. Bernstein's server.
The Internet is a graveyard of good ideas that arrived at the wrong time.
Checking What's on Port 553
If you're curious whether anything is listening on port 553 on your system:
If you see something there, it's almost certainly not PIRP. It might be malware squatting on an unused port, or it might be custom software that chose 553 arbitrarily. Either way, investigate it.
Legitimate traffic on port 553 is rarer than PIRP implementations.
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