The liveness check for IKEv2 is similar to Dead Peer Detection (DPD), which IKEv1 uses as the way to determine whether a peer is still available.

In IKEv2, the liveness check is achieved by any IKEv2 packet transmission or an empty informational message that the gateway sends to the peer at a configurable interval, five seconds by default. If necessary, the sender attempts the retransmission up to ten times. If it doesn’t get a response, the sender closes and deletes the IKE_SA and corresponding CHILD_SAs. The sender will start over by sending out another IKE_SA_INIT message.