How to set routes for my vpn connection

9. Now click on the “IPv4 Settings” tab and click “Routes…”
10. Click “Add” and in the “Address” box, enter the IP address of the machine you which to access. For our XYZ server, this is “203.0.113.3”. In the “Netmask” box enter “255.255.255.255” (to indicate we only want this single IP address). Leave the Gateway and Metric boxes empty.
11. Select “Use this connection only for resources on its network”
12. Click “Ok” on the “Editing IPv4 routes” box
13. Click “Save…”

Copy from http://blog.rac.me.uk/2013/10/20/linux-setting-up-a-vpn-to-only-route-specific-ip-addresses/

I'm using the VPN to connect to my internal network, at the office. I want to keep my internet access using my provider, but I also want to access several machines within the office.

To do so, I select:

• Use this connection only for resources on its network
• Add a new route with:
  • IP address: 192.168.100.0 (the address of my office network; not just one specific machine)
  • Netmask: 255.255.255.0
  • Gateway: 192.168.100.143 (I get the IP from the route table after connection the VPN for the first time).
  • Metric: 1

This command line do the same as the above configuration:

sudo route add -net 192.168.100.0/24 gw 192.168.100.143 metric 1

Afterwards, I can connect to any office host on that network, using ssh, remmina, etc.

I got "address", "netmask", and "gateway" in this way:

1) connect to VPN normally

2) run "ifconfig" command. output is somthing like this:

eth0      ....
          .... 

lo        ....
          .... 

ppp0      Link encap:Point-to-Point Protocol  
          inet addr:172.16.11.15  P-t-P:172.16.11.1  Mask:255.255.255.255
          .... 
          .... 

now:

• set 'address' as the IP address you want to connect to it through VPN
• set 'netmask' as 'mask' value in ppp0 output
• set 'gateway' as 'p-t-p' value in ppp0 output