Dead Peer Detection (DPD) is the method to detect the aliveness of an IPsec connection. During IPsec tunnel creation, VPN peers will negotiate to decide whether to use DPD or not. When DPD is in use, the router will send DPD packet Are_You_Thereto the VPN peer and wait for peer’s ACK. If there is no feedback from the peer, it will disconnect the IPsec tunnel.
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