Lesson 2.9: Subnets and CIDR: dividing a network
Why networks are divided into subnets (size, performance and, above all, security: keeping guests, cameras and servers apart), how CIDR prefix lengths set the size of each subnet, and how to plan addresses so the pieces fit. In the lab you turn one /24 block into four subnets for a new office, check each one's range and size, and work out which subnet a device belongs to.
19 min
You will learn to
- Explain why networks are subnetted, especially for security
- Calculate the size of a subnet from its prefix length
- Split a /24 into smaller subnets
- Find the subnet an address belongs to
- Explain network segmentation
Key terms
- Subnet
- A smaller network carved out of a bigger address block, with its own network and broadcast address.
- CIDR
- Writing a network as an address plus a prefix length (10.20.0.64/27), so networks can be any power-of-two size.
- Prefix length
- The number after the slash: how many bits are the network part. The rest are host bits.
- Usable hosts
- 2 to the power of the host bits, minus 2 (network and broadcast).
- Network segmentation
- Dividing a network into zones and controlling the traffic between them, so a problem in one zone doesn't spread to the others.
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