Dividing address space.
WHAT A SUBNET IS
A defined range of addresses treated as one local network.
WHAT DEFINES IT
An address and a mask, which together say which part identifies the network and which identifies the device.
WHY IT MATTERS
Devices in the same subnet communicate directly.
Devices in different subnets communicate through a router.
WHAT THAT EXPLAINS
Why two devices on the same switch sometimes cannot reach each other.
If their addresses place them in different subnets, they cannot, without routing.
WHAT A TYPICAL SMALL NETWORK USES
A single subnet large enough for its devices.
WHEN TO USE MORE
Separating groups of devices Larger networks
WHAT GOES WRONG
A device configured with the wrong mask Two subnets overlapping A device configured for one subnet plugged into another
HOW TO SPOT IT
The device has an address but cannot reach the router.
WHAT TO CHECK
The address, the mask, and the gateway, together.
They must be consistent.
