The Hyper-V host's virtual machine console listener — RDP to a VM's screen, not to the VM's own network stack.
IANA registers 2179 as vmrdp, "Microsoft RDP for virtual machines". The Hyper-V host's Virtual Machine Management Service listens here, and VMConnect (the Connect button in Hyper-V Manager, and the same path used by System Center VMM) uses it to attach to a guest's console. Because the connection terminates at the hypervisor, it works whether the guest is booting, crashed, or has no network configured at all — which is exactly why it is different from plain RDP on 3389. Microsoft's own cluster troubleshooting guidance tells admins to open 2179 for VMConnect, so it shows up on the management NIC of Hyper-V hosts and failover-cluster nodes.
Do not expose
This is console access to every VM on the host, below the guest OS. It belongs on a management network reachable only by Hyper-V administrators.
$ nc -vz TARGET 2179Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.