I want to setup ER5120 behind 2 robustel 4G routers as follows:

1. 4G router #1: eth0 port 192.168.0.1 => WAN port ER5120 (interface #1) 192.168.0.10 (self assigned static IP)

2. 4G router #2: eth0 192.168.2.1 => WAN port ER5120 (interface #2) 192.168.2.10 (self-assigned static IP)

The purpose is to allow an external MQTT client to connect to a cluster of MQTT servers in DMZ@ER5120

3. DMZ port ER5120 (interface #5) 10.216.3.1 is connected to a 8-port switch with 5 Raspberry Pis (3 rabbitmq servers in clustered & 2 HA proxy with a virtual IP 10.216.3.200)

4. LAN port ER5120 (interface #3) 192.168.1.1 is connected to a 26-port smart switch (192.168.1.254) and a mqtt client (192.168.1.120)

When i ping from 192.168.1.120, i am able to reach 10.216.3.200.  This means I can now publish data to the cluster of rabbitmq servers from the LAN segment.

Now i want to make the data available in the internet.  I intend to set up a mosquitto mqtt broker in the cloud and bridge to the virtual IP.

I set the System Mode as non-NAT.

Question:

Q1: from 4G router #1 I can ping ER5120 (192.168.0.10).  How can I configure ER5120 to route request from WAN (interface #1) to DMZ (interface #5)

When i try the following values in Advanced->Routing, i get an error: Destination Network conflicts with the subnet of the Interface. Please enter another one.

a. Destination: 10.216.3.200

b. Subnet mask : 255.255.255.0

c. Next hop: none

d. Interface: DMZ or WAN1

Q2: