It appears packet loss when the protected server message pass through the DDOS system, user network topology is shown below:
The problem will be resolved after turn off the link status detection function on cleaning equipment.
It’s caused due to the link status detection function of cleaning device hasn’t be closed. This is the default configuration of the cleaning equipment, we need to turn off the function in a back and forth path inconsistent networking. The shutdown command is undo firewall session link-state check.