I have been happily connecting to my company's (Cisco IPSec) VPN for many months, but suddenly as of last week I'm not able to use it. When I try to connect from my Mac 10.8.3 machine, the VPN connection initially says 'connected' but when I try to SSH to any machine on the network, all the computers in my house temporarily lose internet connectivity. This makes me think either something changed in the VPN configuration (which the Admin's deny) or perhaps my ISP pushed an update to my Router which is causing this issue, but that also seems unlikely. Any hints regarding Router or OSX settings to check in diagnosing this?
So, it seems like this was a problem with my Router - even after resetting it to Factory settings (!). I plugged in an old router that I had and the VPN is back to working. Very strange :S