ZyXEL Communications ZyWALL USG Series Application Notes page 156

Select Do not dial the initial connection and click Next.
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7 Enter the domain name or WAN IP address configured as the My Address in the VPN gateway
configuration that the USG is using for L2TP VPN (172.16.1.2 in this example).
Click Finish.
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The Connect L2TP to USG screen appears. Click Properties > Security.
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Click Security, select Advanced (custom settings) and click Settings.
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Select Optional encryption (connect even if no encryption) and the Allow these protocols
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