Overview
Port 2 is the second assignable port in the TCP/IP port system. For over three decades, it was officially registered to CompressNET, a commercial network compression protocol. On February 13, 2025, IANA de-assigned it and marked it as Reserved1.
Almost no one noticed.
What CompressNET Was
CompressNET was a commercial product that compressed TCP connections over wide area networks (WANs)2. It used two ports: port 2 for management, and port 3 for the actual compression process. The idea was straightforward: bandwidth was expensive, so compress the traffic before sending it across the wire.
The protocol was registered by Bernie Volz, whose contact was listed as VOLZ@PROCESS.COM in RFC 17003. Volz went on to become a significant contributor to Internet standards, co-authoring RFCs on DHCP, DHCPv6, and TCP implementation problems4. His early work on CompressNET was a footnote in a career that shaped how devices get their IP addresses.
CompressNET itself never achieved wide adoption. The protocol was proprietary, and the problem it solved (expensive bandwidth over WANs) was eventually addressed by cheaper bandwidth and more sophisticated compression built into higher-level protocols. The port assignment outlived the protocol by decades.
The Registry History
Port 2 appears in the Assigned Numbers lineage going back to at least RFC 1340, published in July 1992 by Joyce Reynolds and Jon Postel5. It was carried forward into RFC 1700 in October 19943, and then into the online IANA registry when RFC 3232 moved the Assigned Numbers function out of periodic RFC publications and into a living database6.
For over 30 years, the entry sat there: compressnet 2/tcp Management Utility [BV15].
Then, on February 13, 2025, IANA de-assigned both port 2 and port 3, marking them as Reserved1. Under RFC 6335, "Reserved" means the port is not available for new assignment. It is assigned to IANA itself for special purposes7. This is different from "Unassigned," which would make it available for someone else to claim.
Port 2 was not freed. It was retired.
Security
Port 2 has a minor but real security history. In the early 2000s, a backdoor trojan called "Death" was associated with TCP port 28. The trojan was simple: it opened port 2 for remote access, counting on the fact that almost nothing legitimate listened there. Firewalls and intrusion detection systems like SmoothWall flag unexpected traffic on port 2 as potentially malicious.
The general rule: if something is listening on port 2 in a modern network, it should not be.
How to Check What Is Listening on Port 2
On Linux or macOS:
On Windows:
If anything responds, investigate. There is no modern legitimate service that uses this port.
Port Range
Port 2 belongs to the well-known ports range (0 through 1023). These ports are reserved by IANA for standardized services and, on Unix-like systems, require root or superuser privileges to bind7. The well-known range is where the foundational protocols of the Internet live: HTTP on 80, HTTPS on 443, SSH on 22, DNS on 53.
Port 2 was an early resident of this range. It just never became foundational.
Why Unassigned and Reserved Ports Matter
The port number space is finite: 65,535 ports. The well-known range is even smaller, just 1,024 ports. Every assignment in this range is a claim on a shared resource. When a protocol dies but its port assignment persists, that is a small piece of the commons held by a ghost.
IANA's decision to de-assign ports 2 and 3 in 2025 is a form of housekeeping. It acknowledges that the Internet is not a museum. Protocols come and go. The registry should reflect what is actually in use, not what someone registered in the early 1990s and never came back for.
But "Reserved" status means port 2 will not be reassigned. It sits in a kind of limbo: no longer CompressNET's, not available to anyone else. A door with the nameplate removed but the lock still engaged.
Frequently Asked Questions
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