D-Link DFL-1660 User Manual page 374

9.4.6. IPsec Advanced Settings
Chapter 9. VPN
This setting is used with IKEv1 only.
Default: 2 (in other words, 2 x 10 = 20 seconds)
DPD Expire Time
The length of time in seconds for which DPD messages will be sent to the peer. If the peer has not
responded to messages during this time it is considered to be dead.
In other words, the length of time in seconds for which DPD-R-U-THERE messages will be sent. If
the other side of the tunnel has not sent a response to any messages then it is considered to be dead
(not reachable). The SA will then be placed in the dead cache.
This setting is used with IKEv1 only.
Default: 15 seconds
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