Billion BiPAC 7404V series User Manual page 111

VoIP/(802.11g) ADSL2+ (VPN) Firewall Router
Example: Configuring your Router to Dial-in to the Server
Currently, Microsoft Windows operation system does not support L2TP incoming service.
Additional software may be required to set up your L2TP incoming service.
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Appendix A: Product Support and Contact Information