API port 9100 not opening and "ROON" displayed on Windows 11 browser (ref#E2U7R9)

Support
1

Hi! What’s not quite right with Roon?

· None of the above quite fits

None of the above quite fits

· None of these quite match

Tell us what's going on

· API port 9100 willl not open. and http://172.22.16.207:9330/display/ show only "ROON" at windows11 Browser.

Tell us about your home network

· All in Lokal Network the core server run on win11 at ESXi. Roon ARC open. RoPieee Working fine.

2

Hi @stephan_wegmueller,

Thanks for writing in and for sharing your report! We didn’t see any error messages, port binding failures, or any mention of ports 9100 or 9330 in any of your Roon Server logs. This means the issue is likely not being logged by Roon Server itself, it’s a network/firewall/OS-level problem outside of Roon.

Port 9100 is Roon’s extension/API port. It not opening typically means:

  • Windows Firewall is blocking it. This is the most common cause on Win11. Roon may have a rule for its main app but not for the specific inbound port 9100.
  • The ESXi VM's virtual NIC or port group is filtering it. ESXi VMs with a firewall appliance in the virtual switch can silently drop ports.
On the Win11 VM, run in an elevated PowerShell: 
netstat -an | findstr ":9100"

If you see LISTENING on 0.0.0.0:9100, the port is open on the OS — the issue is the firewall. If nothing appears, Roon isn’t binding to it yet (try restarting Roon).

Then explicitly allow it through Windows Firewall:

New-NetFirewallRule -DisplayName "Roon API 9100" -Direction Inbound -Protocol TCP -LocalPort 9100 -Action Allow

The “ROON” text on a blank page is the expected placeholder when no display client is actively connected or configured. This is not an error — it means the web server is actually working. The display feature requires a Roon client (like the Now Playing screen or a Roon-compatible display device) to be actively sending data to that endpoint.

  1. In the Roon app, go to Settings → Displays and ensure a display is set up and enabled for that zone.
  2. Try opening the display URL from inside the Roon desktop app itself first, or use the Roon remote on a phone to push Now Playing to the display.
  3. Make sure port 9330 is also allowed through the Windows Firewall with the same command above (replacing 9100 with 9330).

Please note that we don’t fully support the use of VMs, and so another good troubleshooting step would be to test functionality across a normal LAN.

Thank you! :folded_hands:

3
Hi Benjamin,

I finally understood the idea behind the 9330/display/ endpoint and how it works.

Since I wasn’t able to establish a direct API connection, I installed the MQTT extension instead:

fjgalesloot/roon-extension-mqtt – Roon Extension to integrate Roon into home automation systems using MQTT.

It does exactly what I wanted.

Thank you very much for the quick reply and the clear explanations.

Roon is really great.

Greetings,
Stephan