What is a subnet and how does it divide an IP address?

Question

Accepted Answer

A subnet is a set of hosts that share the same network portion and can reach each other directly (Layer 2) without going through a router.
The network/host split of an IP address is what defines a subnet: every host whose network portion matches is "local" to each other. Two hosts in the same subnet talk directly over the switch; two hosts in different subnets must hand their packets to a router. This is the single rule that determines "do I deliver this myself, or send it to the gateway?"

Part
Role

Network portion
High-order bits — names the subnet (shared by all members)

Host portion
Low-order bits — names the individual device

Behaviour:

same subnet → direct delivery, Layer 2 (MAC/switch)
different subnet → must route, Layer 3 (IP/router)

Example:
192.168.1.0/24 subnet:
- 192.168.1.1 (host 1)
- 192.168.1.2 (host 2)
- Same network portion: 192.168.1
- Different host portion: .1, .2

Part	Role
Network portion	High-order bits — names the subnet (shared by all members)
Host portion	Low-order bits — names the individual device