strongSwan

HI All, I have been struggling to resolve this issue for over 2 weeks now with no head way.

im configuring a site-to-site vpn with centos7 and strongswan 5.2, when try to start the vpn connect
i get the showing errors

<pre>
initiating IKE_SA mtn-zin[1] to 41.220.79.242
generating IKE_SA_INIT request 0 [ SA KE No N(NATD_S_IP) N(NATD_D_IP) ]
sending packet: from 178.79.179.231[500] to 41.220.79.242[500] (300 bytes)
retransmit 1 of request with message ID 0
sending packet: from 178.79.179.231[500] to 41.220.79.242[500] (300 bytes)
retransmit 2 of request with message ID 0
sending packet: from 178.79.179.231[500] to 41.220.79.242[500] (300 bytes)
retransmit 3 of request with message ID 0
sending packet: from 178.79.179.231[500] to 41.220.79.242[500] (300 bytes)
retransmit 4 of request with message ID 0
sending packet: from 178.79.179.231[500] to 41.220.79.242[500] (300 bytes)
retransmit 5 of request with message ID 0
sending packet: from 178.79.179.231[500] to 41.220.79.242[500] (300 bytes)
giving up after 5 retransmits
establishing IKE_SA failed, peer not responding
</pre>



Please i need help on this. Thanks