DevOps · interactive
IP addresses, subnets and CIDR
An IPv4 address is 32 bits. The number after the slash says how many of them are fixed for the network; the rest number the hosts inside it. Fewer host bits, smaller network.
10.0.0.0/16
0000101000000000hhhhhhhhhhhhhhhh
Colored: 16 network bits. h: 16 host bits.
- Mask
- 255.255.0.0
- Addresses
- 65,536
- Usable hosts
- 65,534
- First
- 10.0.0.1
- Last
- 10.0.255.254
- Broadcast
- 10.0.255.255
10.0.0.0/16 split into /18: 4 subnets
- 10.0.0.0/18 (16,384)
- 10.0.64.0/18 (16,384)
- 10.0.128.0/18 (16,384)
- 10.0.192.0/18 (16,384)
Is it inside 10.0.0.0/18?
- 10.0.0.5 ✓
- 10.0.63.200 ✓
- 10.0.64.1 ✗
- 10.1.0.1 ✗
- 192.168.1.10 ✗
/16 leaves 16 host bits: 2^16 = 65,536 addresses, 65,534 usable.
Split the /16 into
1 2 /16 means the first 16 bits are the same for every address in the network. The mask 255.255.0.0 says the same thing.
Each extra prefix bit halves the size.
3 4
In production
Tools and technologies
Every cloud network starts with a CIDR block.
Not tied to one language — use these names when you search docs or design a system.