Draytek VigorIPPBX 3510 User Manual page 59

You may further specify the method you use to get IP, the security method, and
authentication method. If the Pre-Shared Key is selected, it should be consistent with
the one set in VPN router.
If a PPP-based service is selected, you should further specify the remote VPN server IP
address, Username, Password, and encryption method. The User Name and Password
should be consistent with the one set up in the VPN router. To use default gateway on
remote network means that all the packets of remote host will be directed to VPN
server then forwarded to Internet. This will make the remote host seem to be working
in the enterprise network.
VigorIPPBX 3510 Series User's Guide
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