Port 1642 belongs to the registered ports range (1024–49151), where organizations and developers can register specific services with IANA. It's officially assigned to a service called isis-am, which appears to be related to IS-IS routing protocols.
But here's the strange part: there's almost no evidence this service is actually used.
What isis-am Was Supposed to Be
The name "isis-am" likely stands for something related to the IS-IS (Intermediate System to Intermediate System) routing protocol—a link-state routing protocol used in large enterprise and service provider networks.1
IS-IS itself operates at Layer 2 of the OSI model and doesn't use traditional TCP/UDP ports for its core routing functions.2 The protocol exchanges routing information directly at the data link layer, not through the transport layer where port numbers live.
So what was port 1642 for? Possibly an application layer management tool, a multiplexing service, or an extension to the core IS-IS protocol. The registration exists, but the documentation doesn't.
The Archaeology Problem
When you search for information about port 1642, you find:
- IANA listings confirming the registration3
- Port database sites echoing that same registration
- No RFCs documenting the protocol
- No vendor documentation explaining how to use it
- No security advisories about vulnerabilities in it
- No forum posts from administrators troubleshooting it
A port can have a name and still be invisible. Port 1642 is registered to isis-am, but finding evidence of its actual use is like searching for a ghost.
Why Unassigned and Unused Ports Matter
The IANA port registry contains thousands of entries. Many were registered in the early days of the Internet for protocols that never gained widespread adoption. Some were used briefly and then abandoned as better solutions emerged. Others were registered "just in case" and never actually deployed.
Port 1642 appears to be one of these—a registered name without a real history.
This matters because:
Security scanners flag unexpected listeners — If something shows up on port 1642 in your network scan, it's worth investigating. The legitimate service is so rare that any activity here is unusual.
The port is available for unofficial use — Because the registered service isn't widely deployed, port 1642 might be quietly used by custom applications that needed a port number and picked one that seemed unoccupied.
It's a reminder that registration ≠ deployment — Just because a port has an official name doesn't mean anyone is using it. The registry is aspirational; actual Internet traffic tells the real story.
How to Check What's Listening
On Linux/macOS:
On Windows:
If you find something listening on port 1642, investigate what process owns it. The official isis-am service is so obscure that any activity here warrants a closer look.
The Registered Range
Port 1642 sits in the registered ports range (1024–49151), where:
- Organizations can register specific services with IANA
- Registration is voluntary and doesn't guarantee the port won't be used for other purposes
- Many registered ports have fallen into disuse as technologies evolved
Unlike well-known ports (0–1023), which require root privileges to bind on Unix systems, registered ports can be used by any user process. This makes them both more accessible and more prone to unofficial appropriation.
What We're Left With
Port 1642 has a name: isis-am. It has a registration. It exists in databases and scanning tools.
What it doesn't have is a story. No moment of creation where an engineer solved a problem. No widespread deployment. No community of users who depend on it.
The IANA registry is full of these—ports registered decades ago for protocols that never gained traction, or were used so rarely they left no archaeological trace. Port 1642 is one of them.
If you encounter traffic on this port, you're not seeing the registered service. You're seeing something else that borrowed the number.
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