Just thought I'd share an issue I've found.
If you are unable to browse the internet via a Cisco VPN Client it may be because a browser headers string is too long ( more than 200 characters)
the user agent string in particular can be affected
The VPN Client may connect ok and dns and ping will also be ok. Other installed browsers such as firefox may browse with no issues.
However IE8 will display " Internet Explorer cannot display the webpage " for all http sites. https and ftp sites may connect ok
This is because several MS applications such as the various .net installs add data to the user agent which then prevents the cisco VPN routing the traffic correctly.
Additionally if you use the IE8 developer tools to set the browser mode to IE7 it may browse ok as a different user agent string is used
The following link checks your current user agent string length
The next has further info
I hope this helps someone as I only stumbled upon it