When you create a network using the GUI, NetSim will automatically configure the IP address to the devices in the scenario. Consider the following scenarios:
If you create a network with two wired nodes and L2_Switch, the IP addresses are assigned as 126.96.36.199 and 188.8.131.52 for the two wired nodes. The default subnet mask is assigned to be 255.255.0.0. It can be edited to 255.0.0.0 (Class A) or 255.255.255.0 (Class C) subnet masks. Both the nodes are in the same network (184.108.40.206).
Similarly, if you create a network with a router and two wired nodes, the IP addresses are assigned as 220.127.116.11 and 18.104.22.168 for the two wired nodes. The subnet mask is default as in above case, i.e., 255.255.0.0. The IP address of the router is 22.214.171.124 and 126.96.36.199 respectively for the two interfaces. Both the nodes are in different networks (188.8.131.52 and 184.108.40.206) in this case.
The same logic is extended as the number of devices is increased.