Draytek Vigor2910 Series User Manual page 260

Request Background: Some of users think it is not really environment recovery
detection to borrow VPN tunnels from branches for connecting with the headquarters.
The system should connect to headquarters automatically and that is called ERD.
To set ERD AutoDrop mode
To check current status of AutoDrop
> vpn Trunk backup ERD VpnBackup AutoDrop
To set AutoDrop
> vpn Trunk backup ERD VpnBackup AutoDrop 3600
Why use <second> - AutoDrop might cause unstable condition for data
transmitting. To solve the problem, you can set value for second to specify
valid time for sending data out.
When set value for <second> with "0": VPN tunnel that does not join
Member1 will try to connect with VPN server of Member1 for every six
seconds. Once the connection is successful, current transmitting data (mail,
video conference, or other) will be dropped immediately.
When set value for <second> with "1 ~ 4294967295": The administrator can
try to connect with VPN server within certain time. Once the connection is
successful, current transmitting data (mail, video conference, or other) will be
dropped immediately. For example, if you type "3600" as the value for
<second>, AutoDrop will be done with 30 seconds (3531 ~ 3600) for the
backup VPN tunnel. If you set "30" as the value for <second>, it will be
regarded as "0".
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Vigor2910 Series User's Guide