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Slow wifi with Sonicwall Global VPN

If you have GVC running connected or not and notice slow speed tests (.1mbps down) but fast uploads and no drop connections please do the following.

Solution / Workaround is to disable Receive Segment Coalescing (RSC) on the wifi adapter.

Automated fix from Microsoft available here, https://aka.ms/diag_cssemerg11005

Manual disabling RSC

Open an Administrative powershell. Start menu and search for powershell and right click and run as administrator.
get-netadapter (This gets the network adapter names)
get-netadapterrsc (Get the network adapter's RSC settings for each adapter)
disable-netadapterrsc -name ADAPTER-"NAME" ( Disable-NetAdapterRsc -name "Wi-Fi" ) (This disables RSC for the named adapter, get name from step 3, usually Wi-Fi)
get-netadapterrsc (Verifies RSC status)

To determine RSC problem.

Please install speedtest.net app (no login required, just skip) . Speedtests in browser when you have slow downloads sometimes crashes the browser.
Run the speedtest. If you get a good speeds 100-400mbps, then continue to Step 4.
If you have slow speeds, turn wifi off and back on to ensure you have the closest accesspoint. Please repeat step 2 to confirm good internet. If its bad, you might have gvc 4.10 installed and downgrade.
Run GVC. It doesn’t have to connect to vpn site to break wifi downloads with RSC.
Do a speedtest. If you notice considerably slower downloads but normal uploads then you have a RSC problem.

Creation date: 4/23/2019 9:48 PM Updated: 7/7/2020 2:51 PM