How to properly configure route to exclude the provider's subnet from the VPN connection?

Question

VPN

Kind.
Note. Xubuntu 14.04. Connected wifi to the router, so just for reference. Rise L2TP-IPsec VPN connection with purchased VPN for a pleasant and unlimited surfing.
Question. How to exclude an ISP address range from a VPN connection. And then the provider has an internal LAN for 100mb, well, you can’t enter the billing through vpn. The option to enable/disable VPN as needed is too complicated for me ;-)

Answer 1

What OS is being used? Generally on good in this case it is necessary to use routing metrics. For the VPN metric (as I understand it, all outgoing connections become your main gateway) we set 10, and for the provider subnet 1.
Depending on the Linux / Windows OS used, the syntax will differ.

Answer 2

Look at the routing before connecting vpn and after.
If the provider uses a large mesh and does not provide all dhcp routing, then you need to find out the range you need and add it after raising the vpn.
Since before raising the gateway, the default gateway was the provider, then everything worked. After lifting, VPN default gateway.
We must also remember that vpn can issue its own DNS and if names are used within your network, then they will not work. There is usually an option that allows you to not accept DNS VPN. We must remember that there must be routing to DNS.