VPN site to site between fortigate, behind peplink

Dear all,
I want to setup vpn site to site two fortigate 100E, but fortigate behind peplink 380.![image.png|819x808]

Please help me config vpn site to site between two fortigate 100E (fortigate behind peplink 380) with this topology.
Many thanks,

How many public ips do you have on each end?
What services are in use on the peplink 380s?
A couple of simple ways to do this come to mind.
Drop in mode on the 380’s to allow the ip to be shared between the peplink and the fortigate.
1-1 NAT and map an additional public ip to the wan ip of the fortigate.
Use peplink for the vpn tunnels and do static routes in the fortigate to reach the desired traffic.

thanks for reply Jonathan_Pitts,
I have 5 IP public on each site,
Peplink in use public service and NAT
Fortigate in use routing vlan and policy (not NAT)
I don’t know have to public port UDP 500 and 4500 on Peplink and create policy on each fortigate to vpn site to site

On the pepwave setup 1-1 nat using one of the extra public ip’s and may to forinets wan ip.

Do an outbound policy to map the same public ip.

or use port forward
Remote IPsec VPN access UDP/IKE 500, ESP (IP 50), NAT-T 4500
Remote SSL VPN access TCP/443 (by default; this port can be customized)
SSO Mobility Agent, FSSO TCP/8001
to the ip of the fortinet.
Do an outbound policy to map the same public ip.

many thanks Jonathan_Pitts.

We have 2 options to config on this case.

  1. Using PepVPN
  2. Use Forti IPSec Tunnel.
    I choose Forti IP Sec Tunnel because I can apply many policies for VPN.