I deployed a Sonicwall NSA 3500 in March of 2010 for my employer. We also have a 50x50 fiber connection from EPB. I had noticed that our network felt great on everything but Apple and their respective services (iTunes, Software Update, etc). They were fast sometimes and extremely slow at others.
After much research, I finally came across this thread over at Apple’s support forums. Since we are still under warranty on this firewall, I wanted to discuss the change with Sonicwall first. I logged a support ticket and included a link to that thread. The technician at Sonicwall said that was exactly what I needed to do.
I made the change last time and everything is working much better.
Here is a quick walk through (don’t do this without talking with Sonicwall first)
1. Log into the SonicWALL web interface
3. Click Internal Settings
4. Under Security Services Settings locate and checkmark Enable enforcement of a limit on maximum allowed advertised TCP window with any DPI-based service enabled
5. Set Max TCP window to 256
6. Make sure to click Apply at the top of the page