Draytek Vigor2120 series User Manual page 265

IPsec Security Method
After finishing all the settings here, please click OK to save the configuration.
from remote dial-in user, Certificate (X.509) and
Pre-Shared Key.
Certificate for Dial-in –Choose one of the local certificates
from the drop down list.
Pre-Shared Key- Specify a key for IKE authentication.
Confirm Pre-Shared Key- Retype the characters to
confirm the pre-shared key.
Note: Any packets from the remote dial-in user which
does not match the rule defined in VPN and Remote
Access>>Remote Dial-In User will be applied with the
method specified here.
Medium - Authentication Header (AH) means data will be
authenticated, but not be encrypted. By default, this option
is active.
High (ESP) - Encapsulating Security Payload (ESP) means
payload (data) will be encrypted and authenticated. You
may select encryption algorithm from Data Encryption
Standard (DES), Triple DES (3DES), and AES.
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Vigor2120 Series User's Guide