Your best bet seems to be AppleScript:
tell application "System Events"
tell current location of network preferences
set VPNservice to service "VPN (L2TP) 2" -- name of the VPN service
if exists VPNservice then connect VPNservice
As for entering a username and password, I'm not sure how you could do that. Further scripting could get you the frontmost window and input the username and password, then submit the dialog, but as I don't have a Cisco VPN to test I couldn't tell you how to set that up.
If you have the actual Cisco VPN client installed (which afaik is not necessary), you could just use this command:
open /Applications/VPNClient.app --args -c -user <YourUsername> -pwd <YourPassword> <ProfileNameToConnect>