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🌐 IPv4 Subnet Calculator
Calculate subnet masks, network addresses, and host ranges
About IPv4 Subnetting
Subnetting is the practice of dividing a network into smaller sub-networks. This calculator helps you determine network addresses, broadcast addresses, host ranges, and other subnet information based on an IP address and subnet mask.
CIDR Notation
CIDR (Classless Inter-Domain Routing) notation uses a slash followed by a number (e.g., /24) to indicate how many bits are used for the network portion of the address.
| CIDR | Subnet Mask | Usable Hosts |
|---|---|---|
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /26 | 255.255.255.192 | 62 |
| /27 | 255.255.255.224 | 30 |
| /28 | 255.255.255.240 | 14 |
| /29 | 255.255.255.248 | 6 |
| /30 | 255.255.255.252 | 2 |
IP Address Classes
- Class A: 1.0.0.0 to 126.255.255.255 (Default mask: /8)
- Class B: 128.0.0.0 to 191.255.255.255 (Default mask: /16)
- Class C: 192.0.0.0 to 223.255.255.255 (Default mask: /24)
- Class D: 224.0.0.0 to 239.255.255.255 (Multicast)
- Class E: 240.0.0.0 to 255.255.255.255 (Reserved)
Private IP Ranges
- Class A: 10.0.0.0 to 10.255.255.255 (10.0.0.0/8)
- Class B: 172.16.0.0 to 172.31.255.255 (172.16.0.0/12)
- Class C: 192.168.0.0 to 192.168.255.255 (192.168.0.0/16)
Frequently Asked Questions
What is a subnet mask?
A subnet mask is a 32-bit number that divides an IP address into network and host portions. It determines which part of the IP address identifies the network and which part identifies the specific host on that network.
What does /24 mean in CIDR notation?
/24 means the first 24 bits are used for the network portion, leaving 8 bits for hosts. This equals a subnet mask of 255.255.255.0 and provides 254 usable host addresses (256 total minus network and broadcast addresses).
What is the difference between total hosts and usable hosts?
Total hosts includes all possible addresses in the subnet. Usable hosts excludes the network address (first address) and broadcast address (last address), which cannot be assigned to devices. Usable hosts = Total hosts - 2.
What is a wildcard mask?
A wildcard mask is the inverse of a subnet mask, used primarily in access control lists (ACLs). Where a subnet mask has 1s, a wildcard mask has 0s, and vice versa. For example, subnet mask 255.255.255.0 has wildcard mask 0.0.0.255.
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