What Range This Port Belongs To
Port 3188 is a registered port — also called a user port — in the range 1024 to 49151. These ports are assigned by IANA through a formal review process, sitting between the well-known system ports (0–1023) and the ephemeral dynamic ports (49152–65535).
Registered ports don't require elevated privileges to open on most operating systems, unlike well-known ports below 1024. Any process can bind to them.
The IANA Registration
IANA lists port 3188 as brcm-comm-port, registered to Broadcom for both TCP and UDP. 1
That's nearly all the official documentation that exists. There's no RFC, no public spec, no description of what the protocol does or who should be running it. The registration exists, but whatever Broadcom built on top of it isn't documented publicly.
Where You Actually See It: Citrix NetScaler
Despite the Broadcom registration, port 3188 turns up most visibly in Citrix NetScaler Gateway configurations. The NetScaler Gateway Plugin — used for VPN, XenApp, and XenDesktop connections — cycles through UDP ports 3108, 3168, and 3188 to establish VPN tunnels using secure ICA connections. 2
If you see UDP traffic on port 3188 in a corporate environment, Citrix infrastructure is the likely explanation.
How to Check What's Listening
If port 3188 is open on a machine you control:
macOS / Linux:
Windows:
Match the PID from netstat to a process name in Task Manager, or run:
Why Unassigned-in-Practice Ports Matter
The registered port range was designed so applications could claim a number and avoid collisions. But registration doesn't require implementation, documentation, or even continued use — it just reserves the number.
Port 3188 illustrates the gap between the registry and reality. It's formally Broadcom's, informally Citrix's, and practically whatever your network decides to run there. When you see it in a firewall rule or a port scan, the IANA label is a starting point for investigation, not a complete answer.
Frequently Asked Questions
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