[CF1] windows error with clientless web isolation (#21406)

* [CF1] windows error with clientless web isolation

* update

Author: deadlypants1973

src/content/docs/cloudflare-one/faq/troubleshooting.mdx

@@ -319,3 +319,19 @@ You must ensure the host device is included in the WARP tunnel while excluding t
 1. Review the WSL2 environment's IP address and compare it with the laptop’s IP.
 2. Check if the WSL network is [included in the split tunnel configuration](/cloudflare-one/connections/connect-devices/warp/configure-warp/route-traffic/split-tunnels/#change-split-tunnels-mode).
 3. If the WSL network is included, exclude it from the split tunnel to prevent connectivity issues.
+
+## Clientless Web Isolation is loading with a blank screen on a Windows device.
+
+This issue can occur due to a conflict between browser settings and Windows network configuration.
+
+In Chromium-based browsers like Chrome and Edge, the **Anonymize local IPs exposed by WebRTC** flag (`chrome://flags/#enable-webrtc-hide-local-ips-with-mdns` or `edge://flags/#enable-webrtc-hide-local-ips-with-mdns`)  — when set to `Enabled` or left at `Default` — hides local IP addresses by replacing them with mDNS hostnames. Multicast DNS (mDNS) hostnames rely on multicast traffic to be resolved properly on the local network.
+
+The [Internet Group Management Protocol (IGMP)](https://www.cloudflare.com/learning/network-layer/what-is-igmp/) allows devices to join a multicasting group. On Windows, `IGMPLevel` determines whether the system participates in multicast group membership. When `IGMPLevel` is set to `0`, multicast support is disabled.
+
+To resolve this error, review the following options:
+
+| `IGMPLevel`        | **Anonymize local IPs exposed by WebRTC** setting         | Result in Clientless Web Isolation           |
+|--------------------|-----------------------------------------------------------|----------------------------------------------|
+| `0` (disabled)     | **Enabled / Default**                                     | ❌ Blank screen                              |
+| `0` (disabled)     | **Disabled**                                              | ✅ Works - browser will use local IP address |
+| `2` (enabled)      | **Enabled / Default**                                     | ✅ Works - mDNS resolves successfully        |

src/content/docs/cloudflare-one/policies/browser-isolation/setup/clientless-browser-isolation.mdx

@@ -139,3 +139,9 @@ If you want to isolate a website without Cloudflare WARP installed, you will nee
   </body>
 </html>
 ```
+
+## Troubleshooting
+
+Review troubleshooting guidance related to Clientless Web Isolation.
+
+- [Clientless Web Isolation is loading a blank screen on a Windows device](/cloudflare-one/faq/troubleshooting/#clientless-web-isolation-is-loading-with-a-blank-screen-on-a-windows-device)