Subnet & CIDR Calculator
Local processing guarantee: IP math executed entirely client-side. No data is sent to servers.
Network Configuration
Enter CIDR range (e.g.
24) or Dotted-decimal (e.g. 255.255.255.0).Initializing calculations...
Understanding IPv4 Subnetting & CIDR
Subnetting is the practice of dividing a physical or logical network into smaller, logical sub-networks (subnets). CIDR (Classless Inter-Domain Routing) was introduced in 1993 to replace the older, rigid Classful network design (Class A, B, and C). It uses the variable-length subnet masking (VLSM) notation where the slash (/) signifies the exact number of bits reserved for the Network ID.
RFC 1918 Private Ranges
Private IP addresses are reserved for internal use within a local area network (LAN) and are not routable on the public internet. They include:
- 10.0.0.0/8 (10.0.0.0 – 10.255.255.255): Single large network.
- 172.16.0.0/12 (172.16.0.0 – 172.31.255.255): 16 contiguous Class B networks.
- 192.168.0.0/16 (192.168.0.0 – 192.168.255.255): 256 local networks, extremely common for home networks.
Special Addresses
Within any IPv4 subnet, the first and last address are reserved for special purposes:
- Network Address: The first address in the subnet (host bits all set to 0). Identifies the subnet itself.
- Broadcast Address: The last address in the subnet (host bits all set to 1). Used to transmit packets to all hosts in the subnet.
- Gateway: Typically the first usable address (e.g. .1) or last usable address (e.g. .254) is assigned to the local router interface.
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