The simplest approach is to use a script to configure it step-by-step. I used a script written by Philplckthun, modified the way to get the server IP: the script file.
Run under Ubuntu:
sh setup. SH
After the configuration configuration is complete, the server side is ready.
Next the client I use Win7, but Win7 has a pit, that is, if there is a router attached, that is, behind the NAT, the default is not connected to L2TP. Found this post on the Internet to solve the problem. You need to modify the registry to create a new DWORD type key in Hkey_local_machine\system\currentcontrolset\services\policyagent. Named AssumeUDPEncapsulationContextOnSendRule, the value is set to 2.
This is not finished, with Win7 default L2TP configuration or connection, because the default authentication method is MSCHAPv2, the script configuration of the server does not support this authentication, change to chap.
Ubuntu 14.04 Shelves IPSEC+L2TP method