What is the three-level hierarchy of subnets and ip addresses? What is the basic idea of subnetting?

The IP address has a hierarchical structure with a length of 32 bits. According to the different bit lengths allocated by the network number and the host number, IP addresses are divided into Class A, Class B and Class C, etc. The traditional IP address is a two-level hierarchy including network number and host number. However, when the number of hosts in the physical network exceeds the limit, or network managers want to group hosts from the perspective of management, then they can divide a large network into smaller networks, that is, subnets. Adding a subnet is actually adding a layer to the IP address system and introducing another subnet number into the IP address.

The IP address of the third level is: net id-subnet id-host id, and the first level defines the address of the node; The second layer defines the physical subnet; The third layer defines hosts and routers.

When dividing subnets, it should be noted that subnets must be physical networks that are very close to each other. It is best to be in a big campus or park.