IP CIDR 计算器
输入 IPv4 CIDR 地址，计算子网掩码、网络地址、广播地址、首末可用主机及主机数量。
What Is the IP CIDR Calculator?
The IP CIDR calculator is a free online tool that computes subnet information from any IPv4 CIDR notation. Enter a network like 192.168.1.0/24 and instantly see the subnet mask, network address, broadcast address, first and last usable host addresses, total host count, and whether the range falls within a private address space.
CIDR notation is used everywhere in networking — cloud VPC configuration, firewall rules, routing tables, Docker networks, and Kubernetes pod CIDRs. This calculator helps network engineers, DevOps teams, and developers quickly verify subnet boundaries without manual binary arithmetic.
How to Use the CIDR Calculator
- Type a CIDR address into the input field, such as 10.0.0.0/8 or 192.168.1.64/26.
- Or click one of the preset buttons to load a common subnet.
- All subnet details update instantly below the input.
Features
- Subnet mask in dotted-decimal notation
- Network address and broadcast address
- First and last usable host addresses
- Total host count and usable host count
- IP class (A, B, C, D/E)
- Private range detection (RFC 1918)
- 5 common preset subnets
- Supports all prefix lengths from /0 to /32
FAQ
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated network prefix length. It is written as an IP address followed by a slash and a number, such as 192.168.1.0/24. The number after the slash indicates how many bits are used for the network portion of the address.
How many usable hosts does a /24 subnet have?
A /24 subnet has 256 total addresses (2^8) and 254 usable host addresses. Two addresses are reserved: the network address (first) and the broadcast address (last).
What is the difference between network address and broadcast address?
The network address is the first address in a subnet and identifies the subnet itself — it cannot be assigned to a host. The broadcast address is the last address and is used to send packets to all hosts in the subnet simultaneously — it also cannot be assigned to a host.
What are the private IP address ranges?
The three private IPv4 ranges defined in RFC 1918 are: 10.0.0.0/8 (Class A), 172.16.0.0/12 (Class B), and 192.168.0.0/16 (Class C). These addresses are not routable on the public internet and are used for internal networks.