DNS Issues after upgrading to 12.5.9 Update 1
We have an M200 currently running Fireware 12.1.B548280.
Last Friday I upgraded to Fireware 12.5.9 Update 1. The upgrade went well. Once the process was completed the box rebooted and all seemed normal until I started getting calls from users not being able to access the internet. When I received the call I was outside the office, I opened my laptop and I was able to connect to SSL VPN. I noticed that quite a few users were also connected to SSL VPN and had access to internal resources. We have our own exchange server, email worked perfectly fine. When I returned to the office that afternoon I noticed that our IP based phone system was working. I went around the office testing computers to browse various sites and all I got was "resolving host" message until the browser times out and get "page cannot get displayed". I tested more than 20 different sites from different computers, same issue in all of them.
I looked at all my policies and all looked just fine. Finally Sunday afternoon I decided to downgrade to previous fireware, the issue went away immediately.
My instinct tells me this is a DNS issue. I keep reading the release notes on Fireware 12.5.9 Update but nothing points me in the right direction.