How to selectively route network traffic through VPN on Mac OS X Leopard?

I don't want to send all my network traffic down to VPN when I'm connected to my company's network (via VPN) from home. For example, when I'm working from home, I would like to be able to backup all my files to the Time Capsule at home and still be able to access the company's internal network.

I'm using Leopard's built-in VPN client. I've tried unchecking "Send all traffic over VPN connection." If I do that I will lose access to my company's internal websites be it via curl or the web browser (though internal IPs are still reachable). It'd be ideal if I can selectively choose a set of IPs or domains to be routed through VPN and keep the rest on my own network. Is this achievable with Leopard's built-in VPN client?

Solution 1:

Create the file /etc/ppp/ip-up with following content:

#!/bin/sh
/sbin/route add <SUBNET> -interface $1 

replacing <SUBNET> with subnet, you want to route through VPN (for ex. 192.168.0.0/16)

execute as root:

chmod 0755 /etc/ppp/ip-up

This file will be executed each time you connect to VPN.

The parameters given to the script:

• $1: The VPN interface (e.g. ppp0)
• $2: Unknown, was 0 in my case
• $3: IP of the VPN server
• $4: VPN gateway address
• $5: Regular (non-vpn) gateway for your lan connections

Solution 2:

There is a hidden feature in Network Preferences on MacOS: you can sort interfaces.

Open System Preferences -> Network -> Click the gear bottom left -> Set service Order...

It's critical that you have your network interfaces sorted into the order you want them to be used. If you want ALL non-LAN data to go to the VPN, put the VPN interface at the top. Sort like this

1. VPN
2. Ethernet
3. Airport

Not like this:

1. Airport
2. Ethernet
3. VPN

This way, no need to check the following setting in Session Options:

Send all traffic over VPN connection

✅ Tested on L2TP VPN connection