Port 170: Network PostScript — A Relic from the Desktop Publishing Revolution

Port 170 sits in the well-known port range (0-1023) with an official IANA assignment for "print-srv"—Network PostScript printing services.¹ It was assigned to Brian Reid at Digital Equipment Corporation's Western Research Laboratory during the desktop publishing revolution of the mid-1980s.²

What It Was Built For

In 1985, the Apple LaserWriter introduced PostScript to the world—a page description language that made professional-quality printing possible on desktop computers.³ As PostScript printers spread across networks, someone needed to figure out how to send print jobs over TCP/IP.

Port 170 was Brian Reid's answer. A standardized port where network-enabled printers could listen for PostScript jobs, and client computers could send documents for printing.⁴

Reid wasn't just any engineer. From 1980 to 1987, he taught at Stanford's computer systems laboratory. Then he joined DEC's Western Research Laboratory in Palo Alto.⁵ From 1986 through 1995, he produced maps of USENET in PostScript—visualizing both its geographical reach and traffic flows. He understood PostScript deeply, and he understood networks.

How It Works

The protocol is straightforward: A client sends a PostScript document to port 170 on a printer or print server. The printer interprets the PostScript commands and renders the page. The entire transaction happens over TCP or UDP.⁶

PostScript itself is a full programming language—resolution-independent, device-independent, and powerful enough to describe any page you could imagine. Port 170 was the door through which those descriptions flowed across networks.

The Reality Today

Port 170 is largely obsolete. Modern printing moved to different protocols—LPR (Line Printer Remote) on port 515, IPP (Internet Printing Protocol) on port 631, or vendor-specific solutions. The desktop publishing revolution came and went. PostScript itself evolved into PDF.

But port 170 remains officially assigned. A fossil in the well-known port range, documenting a moment when the world was figuring out how to make beautiful printed documents work across networks.

Security Considerations

If port 170 is listening on your network, it's either:

• A very old print server still running Network PostScript
• A misconfigured service
• Someone playing with historical protocols

PostScript is a full programming language, which means malicious PostScript code could potentially exploit vulnerabilities in interpreters. If you find port 170 open, investigate what's listening and why.⁷

Modern firewalls should block port 170 unless you have a specific need for legacy Network PostScript printing.

Checking Port 170

To see if anything is listening on port 170:

# Linux/Mac
sudo lsof -i :170
sudo netstat -tulpn | grep :170

# Windows
netstat -ano | findstr :170

# Or use nmap to scan
nmap -p 170 <target-ip>

Why Unassigned and Legacy Ports Matter

The well-known port range (0-1023) is a historical record of the Internet's evolution. Some ports, like 80 and 443, carry the modern web. Others, like 170, document solutions to problems we no longer have.

These legacy assignments matter because:

• They prevent conflicts—nobody else can officially claim port 170
• They document technical history—each assignment tells a story
• They guide security policies—knowing a port's intended use helps identify misuse
• They show how we got here—the Internet wasn't designed all at once

Port 170 represents a specific moment: the mid-1980s, when PostScript was transforming printing, and engineers were building the infrastructure to make it work across networks. Brian Reid saw that problem and assigned a port. The protocol didn't dominate. But the port remains, a small monument to someone's solution.

Related Ports

• Port 515 — Line Printer Daemon (LPR), the more successful network printing protocol
• Port 631 — Internet Printing Protocol (IPP), the modern standard
• Port 9100 — HP JetDirect, raw printing protocol many printers still use