Port 232 belongs to the well-known ports range (0-1023), managed by the Internet Assigned Numbers Authority (IANA). But unlike most ports in this range, port 232 has no official service assignment. It never has.
The Reserved Block
Port 232 sits inside a reserved block spanning ports 225-241.1 This entire range was set aside by Jon Postel—one of the architects of the early Internet and the original keeper of port assignments. The block appears in IANA's registry with the simple notation: "Reserved."2
No RFC defines these ports. No protocol was ever assigned to them. They're gaps in the numbering system, held in reserve for reasons that aren't documented. Maybe they were intended for future protocols that never materialized. Maybe they were kept open for administrative purposes. The records don't say.
What Actually Uses Port 232
While IANA never assigned port 232 to a legitimate service, something else found it: the Skun trojan.3
Skun is a backdoor trojan that exploited port 232 for command and control communications. The malware typically arrived as a ZIP file attached to spam emails and could register itself as a Windows service, record keystrokes, modify IRC client configurations, and send stolen data via FTP or email.4
Malware gravitates toward unassigned ports because they're less likely to be monitored. Port 232 had no legitimate traffic, which made it an attractive choice for attackers who wanted their communications to blend into the background.
The Well-Known Ports Range
Ports 0-1023 are called well-known ports or system ports. They require elevated privileges to bind on Unix-like systems and are assigned through strict IETF Review or IESG Approval procedures.5
Within this range, ports can be in one of three states:6
- Assigned — Currently allocated to a specific service
- Unassigned — Available for assignment upon request
- Reserved — Not available for regular assignment; held for special purposes
Port 232 falls into the third category. It's reserved, which means IANA won't assign it to new services without special consideration. When RFC 6335 was written in 2011, approximately 76% of system ports were assigned.7 Port 232 remains in the 24% that never received an official purpose.
Why Reserved Ports Matter
Reserved ports like 232 serve as buffer zones in the port numbering system. They provide flexibility for future expansion, prevent accidental conflicts, and mark boundaries between different ranges.
The reserved block containing port 232 sits between legitimate services: port 224 (masqdialer) comes just before it, and port 242 (Direct) comes just after.8 The 225-241 range creates a clean separation in the registry.
Reserved doesn't mean unused, though. As the Skun trojan demonstrates, empty ports attract attention from both security researchers and malicious actors. The absence of legitimate traffic can make reserved ports valuable for covert communications.
How to Check Port 232
If you want to see what's listening on port 232 on your system:
On Linux or macOS:
On Windows:
If you see something listening on port 232 and you don't recognize it, investigate immediately. There's no legitimate service that should be using this port.
Security Implications
The presence of traffic on port 232 is a red flag. No standard service uses this port, so any activity here warrants investigation. Network monitoring tools should treat traffic on reserved ports like 232 with suspicion.
The Skun trojan is old malware—it dates back to the early 2000s—but the principle remains relevant. Attackers continue to use uncommon and unassigned ports to avoid detection. Port 232's reserved status doesn't protect it from misuse; if anything, its emptiness makes it attractive for covert operations.
The Gaps in the System
Port 232 represents something important about the Internet's design: not every number needs a purpose. The gaps matter as much as the assignments. Reserved blocks provide flexibility, prevent collisions, and mark boundaries in the numbering system.
Jon Postel reserved ports 225-241 decades ago, and they remain reserved today. The Internet has grown from a research network to global infrastructure, but port 232 still sits empty—officially, at least.
The only traffic that found it was a trojan looking for a quiet place to communicate. That's the truth about reserved ports: they're not empty because nobody wants them. They're empty by design. And sometimes, something unwanted moves into the space nobody was watching.
Frequently Asked Questions
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