if you’re like me and for debugging purposes, you need to get a winxp machine connected to your pptp vpn but do all your work in osx, you have no doubt been as frustrated as i have been. the best answer would have been to switch to an ipsec vpn, but since that wasn’t an option, i was stuck until now.
if you have a new-ish apple intel machine, now you can “share” your vpn connection between your osx machine and a winxp parallels virtual machine running on that same machine.
for this to work, i have found that it is crucial to proceed in a specific order:
1. shutdown parallels vm if it’s running
2. set the networking in parallels’ vm prefs to bridged ethernet
3. goto sharing in osx system preferences on the host machine, then select internet sharing
4. if internet sharing is running, stop it.
5. set share from your default connection (ethernet; i haven’t tried this on airport but it should work)
6. set share to the ethernet adaptor (eth2)
7. start internet sharing
8. boot up your parallels vm
9. connect to your vpn from within parallels; i use winxp and set up a vpn connection in my network connections.
10. i like to verify that i am connected, so fire up firefox and load in a test page, um, i mean google, to make sure you’re connected.
11. if you are, connect your pptp vpn connection and you should have 2 simultaneous connections (both osx host and parallels guest machines) to your pptp vpn from behind a router.