After a VPN connection is created, its status changes to Normal only after servers at both ends of the VPN connection communicate with each other.
If no traffic goes through the VPN connection for a period of time, the VPN connection needs to be renegotiated. The negotiation time depends on the value of Lifetime (s) in the IPsec policy. Generally, Lifetime (s) is set to 3600 (1 hour), indicating that the negotiation will be initiated in the fifty-fourth minute. If the negotiation succeeds, the connection remains to the next round of negotiation. If the negotiation fails, the VPN connection status changes to Not Connected within one hour. The connection can be restored only after the two ends of the VPN connection communicate with each other. The disconnection can be avoided by using a network monitoring tool, such as IP SLA, to generate packets.