how to force split tunnel routing on mac -> cisco vpn

Question

Any one know how to hack the routing table (on a mac) to defeat the forcing of VPN routing for every thing over a cisco VPN? pretty much what I want to do is have only 10.121.* and 10.122.* addresses over the VPN and everything else straight to the internet.

Answer 1

The following works for me. Run these after connecting to the cisco vpn. (I'm using OS X's built-in cisco client, not the Cisco branded client.)

sudo route -nv add -net 10 -interface utun0
sudo route change default 192.168.0.1

Replace "10" in the first command with the network that's on the other side of the tunnel.

Replace "192.168.0.1" with your local network's gateway.

I put it into a bash script, like this:

/Users/mhaase/bin $ cat vpn.sh 
#!/bin/bash

if [[ $EUID -ne 0 ]]; then
    echo "Run this as root"
    exit 1
fi

route -nv add -net 10 -interface utun0
route change default 192.168.0.1

I also found an explanation on how to run this automatically when you connect the VPN, but it's late on Friday and I don't feel like trying it :)

https://gist.github.com/675916

Edit:

I have since left the job where I was using the Cisco VPN, so this is from memory.

The "10" in the first command is the network that you want to route over the VPN. "10" is short hand for "10.0.0.0/8". In Tuan Anh Tran's case, it looks like the network is "192.168.5.0/24".

As for which gateway to specify in the second command, it should be your local gateway. When you log into a VPN that prevents split-tunneling, it is enforcing that policy by changing your routing tables so that all packets are routed on the virtual interface. So you want to change your default route back to what it was prior to getting on the VPN.

The easiest way to figure out the gateway is to run netstat -an before logging into the VPN, and look at the IP address to the right of the "default" destination. For example, here's what it looks like on my box right now:

Internet:
Destination        Gateway            Flags        Refs      Use   Netif Expire
default            10.0.1.1           UGSc           29        0     en1
10.0.1/24          link#5             UCS             3        0     en1
10.0.1.1           0:1e:52:xx:xx:xx   UHLWIi         55   520896     en1    481
10.0.1.51          7c:c5:37:xx:xx:xx   UHLWIi          0     1083     en1    350
10.0.1.52          127.0.0.1          UHS             0        0     lo0

My gateway is 10.0.1.1 -- it is to the right of the "default" destination.

Answer 2

You should be able to ask the administrator of the router you are connecting to to set up a separate "group" that does split tunneling and give you a PCF file that contains the group name and group password for that group.

Answer 3

More than likely your admin should want to set up VPN connections to use local routing for the 10.121.* and 10.122.* subnets and let the remote (your home machine) route all the rest of the requests. (it saves them bandwidth and liability)

Are you using the Cisco's "VPN Client"? os OS X?

if you use OS X's VPN (set up via the networking Preference Pane) you should be able to click "advanced" and select the "VPN on Demand" tab. then supply the necessary subnets for the VPN to use.