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Sometimes you need to deal with VPN software which only runs under Windows. This tip shows you how to configure a Parallels virtual machine to provide a network gateway to these VPNs.

Alternately, there are some newer VPN client applications available for the Mac. Take a look at VPN Tracker, from Equinix; I haven't tried it, but it is well reviewed. Probably worth a look!

0. Make sure you're running 3120 or later and that VM network is set to Bridged.
1. Open /Library/Parallels/.parallels_dhcp_nat in a text editor. If the file is originally empty create [en2] section by adding the line:
[en2]
Now disable Parallels DHCP service by adding the line:
disabled = 1
below [en2]. Restart Parallels DHCP/NAT service by executing the following command from OSX Terminal:
sudo killall -HUP pvsnatd
2. Add a second network adapter to VM and set it to Host-Only Networking and boot your VM.
3. Open Windows network connections, right-click your VPN connection and open properties dialog. Select Advanced tab, enable Internet Sharing and select Local Area Connection that corresponds to Host-Only Networking (you can identify this connection by 169.254.x.x IP address).
4. Open OSX System Preferences -> Network. Select your active network connection (Built-in Ethernet or AirPort) and set it to Manual IPv4 configuration. Be sure to type in the same IP and mask. Now, erase Router field and apply changes.
5. In OSX Network preferences, select Parallels Host-Only and renew DHCP lease. The updated address should be something like 192.168.0.x.
6. You should be all set now. Mac should now use your Windows VM as gateway and DNS server. Start your VPN connection in Windows and see if it works.

To restore Mac network settings set Host-Guest to Manual, erase router address then set primary ethernet connection to DHCP.