There is probably problem with routing table in your system. Try to set default route via eth2 and net 10.10.2.0/24 via eth1.

OS is not concerned.

Check it with CMD

route print

and set required using the following syntax: route ADD destination_network MASK subnet_mask gateway_ip metric_cost

In your example:

route ADD 10.10.2.0 MASK 255.255.255.0 10.10.2.1

of course check where is your default gateway and adjust if necessary

check where is your default gateway and adjust if necessary

Suhaib, first thing I would suggest is, calling the internal network "WAN" is confusing. The WAN is more normally what's on the other side of the router, to the Internet. The internal network, with the server, would be called more appropriately an intranet, perhaps.

The other thing here is that all of the addresses inside your intranet are private IP addresses. And no doubt, according to your chosen IP addresses inside the intranet, the router connected to eth2 of the PC is also a NAPT - network address and port translation gateway. Not just any old router. The NAPT translates addresses, from the Internet side to the intranet side. Hosts in the Internet never see those 10.10.2.x addresses at all. This means that the easiest way for anyone inside the intranet to communicate with anyone on the Internet, is to have the host inside the intranet initiate the session.

Why? Because the IP address and TCP port, used by the host inside the intranet, becomes translated by that NAPT gateway (the router), to appear like something totally different, to devices on the Internet. From the Internet, you would see public IP addresses used, not the private ones you are actually using inside the intranet.

Under normal circumstances, as soon as the session between the host in the intranet and the host on the Internet ends, that mapping of global address/port to private address/port expires. Now you can no longer reach the host inside the intranet, from out in the Internet.

Here's what I would do. Do not connect the router to eth2 of the PC. Instead, connect the router to one of the ports of the core switch, same as the PC and all the other devices.

Then, in order to make your internal server always visible from out on the Internet, you need to manually configure the router for something called "port forwarding."

https://portforward.com/

A port forward is a way of making a computer on your home or business network accessible to computers on the internet, even though they are behind a router. It is commonly used in gaming, security camera setup, voice over ip, and downloading files. After you have forwarded a port you are said to have an open port.

Having done this, you will always be able to see the intranet server from out on the Internet, with a public Internet address that is different from its intranet private address, and the PC will behave as almost every home PC behaves, when connected to a typical home gateway.

Best of luck.