What Port 2555 Is
Port 2555 sits in the registered port range (1024–49151), the middle tier of the port numbering system. Ports here are assigned by IANA to specific services, but unlike well-known ports (0–1023), they don't require elevated privileges to bind. Anyone can open a socket on port 2555.
IANA officially assigned port 2555 to a service called compaq-wcp on both TCP and UDP.1 What "WCP" stood for, what it did, and why Compaq needed a dedicated port for it are questions the public record doesn't answer. The registration exists. The service, as far as anyone can tell, does not — at least not in any form that's left a footprint. It's a tombstone for something that was bureaucratically registered and then forgotten.
The Rootkit Connection
Port 2555 has a more vivid history in incident response reports than in product documentation.
In 2001, the Lion worm spread across Linux systems by exploiting a vulnerability in BIND's TSIG handling (CVE-2001-0010).2 Once inside, Lion deployed the t0rn rootkit — a toolkit for hiding the attacker's presence and maintaining access. Among t0rn's modifications was a trojaned version of in.fingerd, the finger protocol daemon. The altered fingerd opened a root shell on port 2555, silently listening for its author to connect.3
It wasn't subtle by modern standards, but it didn't need to be. In 2001, most administrators weren't watching outbound connections from their servers. The shell sat on 2555, root access waiting, until someone either found it or the machine was wiped.
Lion and t0rn are long obsolete. But port scanners and intrusion detection systems have had 2555 flagged ever since.
Other Observed Uses
Outside the rootkit context, port 2555 has appeared in:
- UPnP device communication — some routers and set-top boxes (including certain DirecTV receivers) have been observed using this port for internal network communication.4
- Custom application stacks — like any unguarded registered port, it occasionally shows up in proprietary protocols and embedded device firmware that picked a number without checking the registry.
None of these are standardized. If you see traffic on 2555, it's worth knowing what it is.
How to Check What's Listening
On Linux/macOS:
On Windows:
The process ID in the output will tell you what's using it. On Linux, sudo lsof -p <PID> gives you the full picture.
Why Unassigned and Forgotten Ports Matter
The registered port range contains thousands of entries. Some are active, maintained services. Some are Compaq WCP — registered once, never updated, the organization that requested them gone or changed beyond recognition.
These ghost registrations matter because they create ambiguity. When you see activity on port 2555, you can't simply look it up and trust the answer. The IANA entry says "Compaq WCP." Your firewall logs say something else. The question of what's actually there requires checking the process, not the registry.
The port system works when registrations are maintained. When they're not, the number becomes unclaimed territory — officially spoken for, practically open.
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