Hello everyone, thanks for advance for your help. 

Iam having a trouble for ping. 

Actually have a site A (wan 10.10.10.254/24 ; lan 192.168.77.1/24) - all ressources are behind this site. 

Then site B (Wan : 192.168.10.254/24 ; lan : 192.168.11.1/24)

Then Site C (WAN : 192.168.81.254/24 ; lan : 192.168.80.1/24)

Then site D (WAN : 192.168.21.254/24 ; Lan : 192.168.20.1/24)

All router are in DMZ from above ISP fiber modem router. 

Those router are communication through ipsec : 

SITE A - B : ping both OK

Site A - C : Ping both OK

Site A - D : Ping both OK

But can't ping site B- site C, site B- site D, site C- site D both side. 

Can't setup an ipsec from those router also (not connecting). 

Does somebody knows how to get communication between between B-C-D ? 

Below an image of the issue. 

Thanks for your kind help !