What Range This Port Belongs To
Port 1735 sits in the registered port range (1024–49151). These ports are not reserved for operating system use like the well-known ports below 1024 are, but they are registered with IANA — the Internet Assigned Numbers Authority — to give applications a predictable, documented home.
Registered ports require an application (and often a named human contact) to stake a claim. IANA records the assignment. The assignment does not mean the software is still maintained, widely used, or even still exists.
The Official Assignment: PrivateChat
IANA lists port 1735 on both TCP and UDP as PrivateChat, assigned to Louis E. Simard.1
That's the entirety of what's known. There is no RFC. No protocol specification. No public documentation of what PrivateChat was or did. The name suggests a private instant messaging application — the late 1990s and early 2000s were full of them — but PrivateChat left no traceable footprint on the public Internet. The registration remains.
This is more common than it sounds. IANA's registry is a historical record as much as it is a living directory. Applications get registered, companies fold, protocols get abandoned, and the port number sits — claimed but vacant.
Observed Unofficial Use: OKBridge
One real-world use does appear: OKBridge, one of the oldest still-running online contract bridge services, uses ports 1729–1735 for its table-serving infrastructure.2 Players connecting to OKBridge tables may see connections on port 1735, particularly when the service routes game traffic across its port range.
OKBridge has operated since the early days of consumer Internet access. Its use of this range predates or coincides with any PrivateChat registration — a reminder that port assignments and port use have always been loosely correlated.
How to Check What's Listening on Port 1735
If you see port 1735 active on your machine and want to know why:
On macOS or Linux:
On Windows:
The process ID from either command can be matched to a running application in your system's process list.
If you see it active on a remote host during a network scan, that's a separate question — one that depends heavily on what software is deployed there.
Why Unassigned and Vacant Ports Matter
The registered port range has over 48,000 possible slots. A meaningful fraction of them are like port 1735: claimed at some point by software that never became widespread, or that no longer exists. This matters for a few practical reasons:
- Firewall rules that block by port number hit legitimate traffic if a running service happens to share a port with a forgotten registration
- Security scanners flag open ports and look them up in registries — if the registry says "PrivateChat" but the actual traffic is OKBridge, the mismatch creates noise
- Port squatting remains a real phenomenon; a registered-but-unused port can be quietly occupied by an application with no official claim
The gap between what IANA records and what actually runs on any given port is where network forensics lives.
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