Please consider the following set up:
SERVER 10.10.10.10---10.10.10.1-f1 SRX1-f2 18.104.22.168---INTERNET----22.214.171.124-f2-SRX2-f1-10.11.11.0/24 hosts
Above we have:
GRE tunnel between SRX1/SRX2 i.e
Tunnel source 126.96.36.199
Tunnel destination 188.8.131.52
Ip address 184.108.40.206/24
We place the tunnel in ZONE A
Also we place the physical interface f1 GRE is riding on in ZONE AA
Tunnel source 220.127.116.11
Tunnel destination 18.104.22.168
Ip address 22.214.171.124/24
We place the tunnel in ZONE B
All hosts on 10.11.11.0/24 will send traffic to 10.10.10.12, which is GRE encapsulated with outer IP HEADER SRC IP 126.96.36.199 DEST IP 188.8.131.52
SRX1 will encapsulate the GRE packet, recover the original packet with src in 10.11.11.0/24 and destination 10.10.10.12
SRX1 is configured with STATIC NAT rule which says If the packet is received from CERTIAN ZONE, and destination IP is 10.10.10.12, then replace the destination IP with 10.10.10.10
So that is how traffic from hosts on 10.11.11.0/24 to Server flows.
Thanks and have a nice day!!
NAT rules are to the ingress and egress interface zones the GRE interface, not the physical interface.
You will also need routes for the remote site to point to the GRE interface