I'm using a Dell Latitude D810 w/ built-in Wifi, EN NIC, a Netopia 802.11b Wifi/EN/DSL router, and Cisco VPN 4.8 on WinXP SP2 for my home office. My VPN performance over Wifi degrades over time from 50+ KB/s (DSL) to 3 KB/Min. Upon disconnecting from the VPN and exiting the VPN SW, my Inet performance immediately jumps to ~1Mbit/sec., and the timeouts I get from web servers disappear. Restarting the VPN SW introduces the same slowness at that point. Reboots help for a bit sometimes. Cisco VPN SW deinstalls/reinstalls as well as VPN profile updates do not alleviate the problem. Using Ethernet instead of Wifi gets the throughput back up (while on Enet, does nothing for Wifi problem). Connecting to various VPN servers takes 20+ seconds when things are slow (Enet and Wifi), and frequently times out (error 427 or 412 usually).
I have reduced the VPN MTU size for my NICs/Wifi/etc., moved VPN from first in the list of LAN connections to try to connect to, read the Cisco release notes for obvious issues, tried UDP and TCP. All to no avail so far.
Thank you in advance for any useful tips!