As per below diagram , establish IPsec tunnel between USG6660 and ALU router for secured data transfer use FTP.
IPsec tunnel not stable . it keep wend down
Network Diagram :-
Perform the continues ping operation to check P2P link stability between USG600 and ALU. while ping IPsec tunnel stable .
after stop the continues ping again IPsec tunnel wend down .
Continues ping result we found that , there is heartbeat issue . we checked ALU node heartbeat rate by default 30sec
after set dpd retransmission interval time 30sec on USG6660 (dpd retransmit-interval 30) . IPsec tunnel stable , there is no interrupted.
DPD (Dead Peer Detection) has to be employed in USG6660 for stable and uninterrupted connectivity.
Type of DPD chosen was "periodic" and the retransmit-interval of DPD packet is 30 seconds which is default for our ALU MPLS node.
ALU node will "reply only" to DPD packets sent by this USG6660.