Subnets and Private vs Public Addresses

Group hosts into subnets

A subnet is a slice of address space that belongs together. Devices in the same subnet typically share a router (default gateway) for traffic that leaves the local network.

Recognize private ranges

Home and office LANs usually use private IPv4 ranges that are not routed on the public internet.

• 10.0.0.0 – 10.255.255.255
• 172.16.0.0 – 172.31.255.255
• 192.168.0.0 – 192.168.255.255

Contrast with public addresses

A public address is unique on the internet and can be reached from other networks (subject to firewalls). Your ISP often gives your home router one public address; devices behind it share it through NAT.

Use the prefix length

/24 means the first 24 bits identify the network, leaving room for local hosts. 192.168.1.0/24 commonly covers 192.168.1.1 through 192.168.1.254 for hosts, with special addresses reserved for the network and broadcast.