Initiator                             Responder
---------------------------------------------------------------------
HDR(CREATE_CHILD_SA), SK {SA, Ni, KEi} -->
                          <--  HDR(CREATE_CHILD_SA), SK {SA, Nr, KEr,
                                   N(ADDITIONAL_KEY_EXCHANGE)(link1)}

HDR(IKE_FOLLOWUP_KE), SK {KEi(1),
 N(ADDITIONAL_KEY_EXCHANGE)(link1)} -->
                               <--  HDR(IKE_FOLLOWUP_KE), SK {KEr(1),
                                   N(ADDITIONAL_KEY_EXCHANGE)(link2)}

HDR(IKE_FOLLOWUP_KE), SK {KEi(2),
 N(ADDITIONAL_KEY_EXCHANGE)(link2)} -->
                               <--  HDR(IKE_FOLLOWUP_KE), SK {KEr(2),
                                   N(ADDITIONAL_KEY_EXCHANGE)(link3)}

HDR(IKE_FOLLOWUP_KE), SK {KEi(3),
 N(ADDITIONAL_KEY_EXCHANGE)(link3)} -->
                               <--  HDR(IKE_FOLLOWUP_KE), SK {KEr(3)}