Free IPv4/IPv6 Subnet Calculator & CIDR Planning Tool
Instantly calculate network ranges, broadcast addresses, and usable host IP counts for any IPv4 or IPv6 CIDR block.
Calculation Results
Enter an IP (v4 or v6) on the left.
What this tool does
This calculator computes network parameters for IPv4 and IPv6 CIDR blocks, including the network address, broadcast address, and usable host range. It determines the subnet mask and wildcard mask based on the provided prefix length. This ensures accurate IP planning and prevents overlapping address space within the infrastructure.
When engineers use this
- Provisioning new VLANs or subnets during site expansion or migration projects.
- Configuring firewall access control lists (ACLs) that require precise wildcard masks.
- Verifying IP ranges for DHCP scopes or static assignment pools to avoid conflicts.
- Troubleshooting connectivity issues caused by incorrect subnet masks on endpoints.
How to interpret the results
- Usable Range: The specific IP addresses available for device assignment, excluding network and broadcast addresses (for IPv4).
- Wildcard Mask: The inverse of the subnet mask, primarily used in Cisco IOS ACL configurations.
- Broadcast Address: The address used to communicate with all hosts on the subnet; traffic sent here is not routed.
What is CIDR?
Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and IP routing. It replaces the older classful network design (Class A, B, C) with a flexible system that allows for more efficient use of IP addresses. A CIDR notation looks like 192.168.1.0/24, where /24 represents the number of bits used for the network prefix.
How to Calculate a Subnet Mask?
A subnet mask determines which part of an IP address belongs to the network and which part belongs to the host. It is calculated by setting the network bits to '1' and host bits to '0'. For example, a /24 prefix means the first 24 bits are ones (255.255.255.0).
IPv4 vs IPv6 Subnetting
IPv4 uses 32-bit addresses, limiting the address space to about 4.3 billion IPs. IPv6 uses 128-bit addresses, providing a virtually infinite address space. Subnetting in IPv6 is simpler in design but deals with much larger hexadecimal numbers. While IPv4 relies on variable length subnet masks (VLSM) to conserve space, IPv6 subnets are typically standardized at /64 for end-user networks.
External References
For more technical details, refer to IANA IPv4 Registry or RFC 4632 (CIDR).