You have Vista or Windows 7 and finally got the latest version of Cisco VPN client (5.0.06.0110) to install and apparently work. All is well until you try to get to some other internal host after a few minutes or more.  Suddenly no other hosts than the original host resolve! You ping your internal DNS server by address and it responds. NSlookup reports timeouts and cant resolve the host name for the internal DNS server. What the heck is going on here? Is it another Cisco “issue”? The clue is that everything works fine on XP but not on Vista/7.  So what changed between XP and Vista/7?  Well, it turns out that Microsoft rewrote the IP stack for Vista/7 and among other things added a nifty little feature called autotune.  This is supposed to automatically tune the recieve window size based on latenacy, usage and the color of your underware.  So guess what?  Since you don’t resolve internal names over the VPN very much (and you have green undies on), name resolution gets tuned down to practically nothing.  So when you try to use it, it times out.  The fix is to turn off autotune. You can do this as follows:

Disable TCP Auto-Tuning

1.Open elevated command prompt with administrator’s privileges.
2.Type the following command and press Enter:
netsh interface tcp set global autotuning=disabled

Enable TCP Auto-Tuning

1.Open elevated command prompt with administrator’s privileges.
2.Type the following command and press Enter:
netsh interface tcp set global autotuning=normal

How about that law of unintended consequences???