http://neworder.box.sk/newsread.php?newsid=13395
This document has a good discussion of the issues with L2TP
Using a Linux L2TP/IPsec VPN server
http://www.jacco2.dds.nl/networking/freeswan-l2tp.html#Firewallwarning
A discussion of Apple Mac L2TP/Ipsec VPN Server and Client
http://www.maclive.net/sid/132
URL wikipedia on L2TP IPSEC
http://en.wikipedia.org/wiki/L2tp#L2TP.2FIPsec
How to set up a Apple Mac Client to VPN to server
http://www.bol.ucla.edu/services/vpn/pptp/docs/macosx.html
the following is quoted from above web site
Instructions for * Mac OS X 10.4 (Tiger)
* Mac OS X 10.5 (Leopard)
* Older versions of Mac OS X
Mac OS X 10.4 (Tiger)
1. Go into your Macintosh hardrive and then Applications Folder. Double-click on Internet Connect.
2. Click on the File menu and select New VPN Connection.
3. In the next window, select PPTP and click OK.
4. In the next window, click on the Configuration section and select Edit Configurations fron the drop down menu.
5. In the next window enter the following information:
* For Server address, type in dns name or ip address of VPN server
* For Account Name, type in your Logon ID.
* For Password, type in your Logon ID password. (optional if you don't want to save your password in the Mac OS X keychain)
Click OK.
6. You have successfully setup your PPTP VPN connection.
Mac OS X 10.5 (Leopard)
1. Click on the Apple Menu > System Preferences > Network.
2. Click on the '+' button to add a new Network Connection.
3. In the next window, select/input the following:
* For Interface, select VPN
* For VPN Type, select PPTP
* For Service Name, type in UCLA VPN
4. In the next window enter the following information:
* For Server address, type in dns name or ip address of server
* For Account Name, type in your Logon ID.
Do not change any of the other options. Click Apply.
5. Click the Advanced button and under the Options tab make sure to check Send all traffic over VPN. Hit OK.
6. (Optional) If you would like to have Mac OS save your key chain password click the Authentication Settings button and enter your UCLA Logon ID password in the password field.
Older versions of Mac OS X
1. Go into your Macintosh hardrive, then into Applications Folder, and double-click on Internet Connect.
2. Go up to File menu and click New VPN Connection Window.
3. In the VPN Connection window:
* For Server address, type in dns or ip address of vpn server
* For User name, type in your Logon ID.
* For Password, type in your Logon ID password. Then click Connect to connect to the vpn server.