Routing between two networks

I have been doing lower skill level networking for years. I am familiar with port forwarding and NAT operations. I have a current issue that is kicking my tail and would like some guidance. I do not know if the pdf will attach so I will describe it here as well...

Internal network #1
192.168.1.xxx
255.255.255.0

A client has provided some equipment that has a small network with 8 devices. This is Internal network #2:

Internal Network #2
192.168.3.xxx
255.255.0.0
(No GW setup)

I need to communicate with one of the devices (192.168.3.253). The manufacturer indicated it is a big deal to change their IP address scheme. They also stated that others had provided a NAT router between the two networks to keep them separate and allow sharing of data.

I have placed a simple router between the two networks. I have tried two different models. Netgear WNR2000v4 and Trendnet TW100-BRV214. Both less than $100 but have DMZ and Port Forwarding. Network #1 is connected to the WAN port. Network #2 is connected to the LAN port.

I have a device on network #1 (192.168.1.202/255.255.255.0) that will poll data from a device on network #2 (192.168.3.253/255.255.0.0). I thought this would be a simple process and setup but am struggling with it. I believe the issue lies in my ignorance of the subnets. When I set up the LAN to have the 255.255.0.0 subnet, It replies that there is a conflict with the WAN IP.

First, Can this link between these two networks be done with a router?

Second, Any suggestions on how to make this work?

Thanks in advance!

Attached Files

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ITLayoutToRussElectric.pdf (5.8 KB)