I experience packet duplication on my workstation with the Cisco VPN client. My set up is as follows.
Windows 2000 Professional SP2
VPN 5000 client v.5.1.10 3DES
The packet duplication only occurs when NOT using the client. For example just browsing the web or pinging. Upon initializing the client the duplicaiton ceases until my session ends. Any non VPN sessions result in packet duplication. I have been able to reproduce the problem on 4 other machines, each with a different NIC. The only common factor is Windows 2000 Pro and VPN client for Win2K.
Windows 95/98/NT machines do not experience this issue. I can only assume it has to do with how the client is bound to the adaptor in Win2K.
Anyone else familiar with this issue please pass on info.