(Unlike IKEv1) the IKEv2 exchange is variable. At best, it can exchange as few as
four packets. At worst, this can increase to as many as 30 packets (if
not more), depending on the complexity of authentication, the number
of Extensible Authentication Protocol (EAP) attributes used, as well
as the number of SAs formed.
So, eight packets is within acceptable range for an IKEv2 negotiation.