When using VPNC to connect through vpn it is possible to only route parts of the traffic from the NIC through vpn.
To do that you need to add a script to your VPNC configuration. It could be stored in this file /etc/vpnc/split
The script needs to be made executable:
The script is documented here and can look like this:
The first line of the configuration (for instance /etc/vpnc/default.conf) should then reference the script like this:
Then when you connect through VPN only IPs starting with 10, 159 and 139 will be routed through VPN.