A Virtual Private Network (VPN) requires a tunneling protocol. Both the client and VPN server must be using the same tunneling protocol. If the VPN server does not support the tunneling protocol with which the client is attempting to connect, the connection will fail.
When you configure a Vista client, you have three options:
- Point to Point Tunneling Protocol (PPTP)
- Layer Two Tunneling Protocol (L2TP)
The ‘Automatic’ option is the default in which case, if IPv4 is being used, the client will try to establish a PPTP connection first, then try L2TP. If you are using Vista SP1 and IPv6, an additional tunneling protocol, called Secure Socket Tunneling Protocol (SSTP), is supported. By selecting the ‘Automatic’ option, the client will try to establish a PPTP connection first, then try L2TP, and then try SSTP.
If your VPN client is configured to use a different tunneling protocol from that supported by the VPN server, you will see an Error 678 message (No answer). The error occurs because there are no ports on the server configured to answer for the specified tunneling protocol. You may also get the error message if all the VPN ports on the VPN server are already in use.
You should also check the protocol configuration in the Properties box for the VPN connection and change it to Automatic or to the protocol setting for which the server is configured to correct this problem.