ZyXEL Communications ZyWALL USG 300 User Manual page 202

Chapter 8 L2TP VPN Example
10 Click Security, select Advanced (custom settings) and click Settings.
Figure 183 Connect L2TP to ZyWALL: Security
11 Select Optional encryption (connect even if no encryption) and the Allow
these protocols radio button. Select Unencrypted password (PAP) and clear
all of the other check boxes. Click OK.
Figure 184 Connect ZyWALL L2TP: Security > Advanced
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ZyWALL USG 300 User's Guide