A subnet with two gateways.

I have some problems understanding a subnet with two gateways.

Let say we have a subnet 192.168.31.0/24. There is a computer (192.168.31.2), two gateways: a router port (192.168.31.1), anoter pc running gateway service (192.168.31.3) (in fact, I don't know what is a gateway service, does it like a http service? you also need a port and ip address to access it?).

• 192.168.31.2 's gateway is 192.168.31.3
• 182.168.31.3 's gateway is 192.168.31.1

When the computer access internet, the packet go to 192.168.31.3, then go to 192.168.31.1. So far, I have no problem.

What will happen when a packet come from internet to 192.168.31.2. Let's say I have a webserver running on 192.168.31.2:80. Please give me as more details as possible.

If 192.168.31.2 is connected to a switch then to a router. How the packet get to it?