i have connected 3 pc to a switch without creating a vlan.two pc having ip address 198.162.20.2 and 198.162.20.3 are pinging with each other but 3rd pc having ip address 125.25.30.2 is not pinging with anyone, why?

could anyone help me why we use the command "switchport mode access" in packet tracer ?switch successfully create vlan without using this command also.

Here i have created a 3 network of IP Addresses 198.162.16.0/20 , 32/20 , 48/20.  configured both the router but while routing the network using ...#network 198.162.16.0 and ....#network 198.162.32.0 in the router-rip mode , network is not getting ad...