CIDR Notation
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Network Information
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Binary Subnet Mask
Common Subnets Reference
| CIDR | Subnet Mask | Usable Hosts |
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What is CIDR Notation?
CIDR (Classless Inter-Domain Routing) notation is a compact way to specify IP address ranges. It combines an IP address with a prefix length (e.g., 192.168.1.0/24) to define network boundaries.
The prefix length indicates how many bits of the IP address are used for the network portion. A /24 network has 256 addresses (254 usable), while a /16 has 65,536 addresses.
Frequently Asked Questions
What does /24 mean in CIDR?
A /24 prefix means 24 bits are used for the network address, leaving 8 bits for host addresses. This gives you 256 total addresses (2^8), with 254 usable for hosts after subtracting the network and broadcast addresses.
How do I calculate subnet mask from CIDR?
The subnet mask is derived by setting the first N bits to 1 (where N is the prefix length) and the remaining bits to 0. For example, /24 gives 255.255.255.0 (24 ones followed by 8 zeros in binary).
What is the difference between network and broadcast address?
The network address is the first IP in the range (all host bits set to 0) and identifies the network itself. The broadcast address is the last IP (all host bits set to 1) and is used to send data to all hosts in the network.
How many usable hosts in a /30 network?
A /30 network has 4 total addresses (2^2) but only 2 usable hosts. The network and broadcast addresses cannot be assigned to devices. /30 networks are commonly used for point-to-point links between routers.