Draytek Vigor2830 Series User Manual page 257

Confirm Pre-Shared Key- Retype the characters to
confirm the pre-shared key.
IPSec Security Method Medium - Authentication Header (AH) means data will be
authenticated, but not be encrypted. By default, this option
is active.
High - 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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