What does the CIDR notation 10.0.1.0/24 mean?
Options
- A network with 24 fixed bits and 8 host bits: 256 addresses (Correct option)
- A group of 24 servers that share the same address
- A network that has exactly 24 addresses in total
- Port 24 on the host whose address is 10.0.1.0
Answer
A network whose first 24 bits are fixed, leaving 8 bits for hosts: 256 addresses
Why
An IPv4 address has 32 bits. /24 means the first 24 bits identify the network and the remaining 8 bits identify devices: 2^8 = 256 addresses (a few are reserved; AWS reserves 5 per subnet).
Quick table: /16 = 65,536 addresses, /24 = 256, /28 = 16. A smaller number after the slash means a bigger network.
You use CIDR ranges to define VPCs, subnets and firewall rules, and ranges must not overlap if you want to connect networks.
Remember
/N = N fixed bits. /24 = 256 addresses.