Can we set filewall rule to control with in subnet? 
[![Network diagram](https://i.stack.imgur.com/esHQV.png)](https://i.stack.imgur.com/esHQV.png)

as in picture 
Can we use firewall to controll PC0 to access only some port on PC1 ?
if we set gateway to router , Is it will alway go to router first? 
In my understanding this 2 PC ( PC0 + PC1 ) can see each other via only switch so they traffic will not pass firewall Is this correct? 

and also if we use 2 subnet on same interface Is this effect to firewall rule? 
same port inrouter we set both ip on same interface 172.17.2.1and 172.17.2.1 as a gate way of both network and have only 1 cable to attached to firewall from router side . Is this ok or we need to seperate port for each subnet or not ?