Splitting one network into smaller isolated ones, and reading CIDR prefixes like /24 and /30.
Subnetting in Practice
In brief
Objectives
- Read a CIDR prefix
- Count usable hosts in a subnet
- Explain why segments are isolated
Subnetting is splitting one network into smaller ones. The /24 in 192.168.1.0/24 means the first 24 bits are the network, leaving 8 bits — 256 addresses — for hosts.
Borrow bits from the host part and you make more, smaller subnets. This is how an organisation gives each department its own isolated segment.
| Prefix | Hosts | Typical use |
|---|---|---|
/24 |
254 | A department LAN |
/30 |
2 | A link between two routers |
/32 |
1 | A single host |
Tip
Usable hosts = 2^(host bits) − 2. The two subtracted are the network address and the broadcast address, which can never be assigned to a machine.
Recap
- The prefix says how many bits are the network
- Usable hosts = 2^host-bits − 2
- Subnets isolate departments from each other