For EACH separate topology assign:
PC0 192.168.1.1 /24
PC1 192.168.1.2 /24
PC2 192.168.1.3 /24
PC3 192.168.1.4 /24
Subnet mask: 255.255.255.0; Gateway blank (same LAN; no router).

PC0 Command Prompt:
ping 192.168.1.2
ping 192.168.1.3
ping 192.168.1.4

Simulation Mode > Add Simple PDU > source PC0 > destination PC3 > Capture/Forward.
