Slow Downloads with Sonicwall NSA 3500
So I was scratching my head today, I needed to download a 2GB file from MSDN via one of our Sonicwall firewalls (NSA 3500 running SonicOS Enhanced 126.96.36.199-33o) and I found that the initial download speed was fine but after a minute or two the speed dropped to almost nothing, however testing the Internet feed using http:\\speedtest.net and downloading the files from different locations all appeared fine with the source. I turned off all the security features one by one to see if that was the cause, no that was not it. After some digging I turned on “Enable enforcement of a limit on maximum allowed advertised tcp window with any DPI-based service enabled”.
You can enable this via a hidden menu by following the below steps.
- Logon to your management webpage.
- Replace main.html in the url to diag.html.
- Select “Internal Settings”.
- Scroll down to “Security Service Settings”.
- Select “Enable enforcement of a limit on maximum allowed advertised TCP window with any DPI-based service enabled”.
- Change “Set a limit on maximum allowed advertised TCP window with any DPI-based service enabled (KBytes)” from 64 to 256.
- Scroll to the top of the page and select “Apply”.