IPv4 Subnet Calculator
Calculate network address, broadcast address, usable IP range, CIDR prefix, and total host capacity with support for /31 point-to-point links.
Best solution
Network diagnostic: IPv4 Subnet Calculator; Network Address, Broadcast IP & Netmask.
- Mask
- 255.255.255.0
- Range
- 192.168.1.1 – 192.168.1.254
- Broadcast
- 192.168.1.255
- Addresses
- 256 total · 254 usable
/31 uses the point-to-point convention; /32 is one host. No network scan is performed.
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Methodology & calculation rule
Bitwise AND operations: Network = IP & Mask; Broadcast = IP | (~Mask); Usable Hosts = 2^(32 - Prefix) - 2 (RFC 3021 /31 yields 2 usable hosts).
Network observations execute bounded requests to public measurement backends (ipify, Google Public DNS, Globalping, or Cloudflare). Measurements distinguish local client configuration from external internet reachability.
No browsing history, private tokens, or credentials are captured. Results are snapshots of external probe vantage points at the recorded observation timestamp.
Real-World Context & Technical Standards
Classless Inter-Domain Routing (CIDR)
RFC 1519 replaced obsolete Class A, B, and C networks with CIDR prefix notation (/0 through /32), allowing variable-length subnet masking (VLSM) to conserve IPv4 address space.
Usable Hosts = $2^{(32 - \text{prefix})} - 2$
For prefixes /0 through /30, the first address is reserved as the Network Identifier and the final address serves as the Directed Broadcast, leaving the intervening range for assignable host nodes.
31-Bit Prefixes on Router Links
RFC 3021 permits /31 subnets on point-to-point router links without reserving separate network or broadcast addresses, perfectly allocating exactly two endpoint IP addresses with zero waste.
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Frequently Asked Questions
What is CIDR prefix notation?
Classless Inter-Domain Routing (CIDR) denotes the number of continuous high-order 1-bits in a subnet mask. For instance, /24 corresponds to 255.255.255.0 and leaves 8 host bits (256 addresses).
Why are two addresses subtracted from the total in /24 subnets?
The first address (host portion all 0s) is reserved as the network identifier, and the final address (host portion all 1s) is reserved as the directed broadcast address.
Why does a /31 subnet have 2 usable hosts instead of 0?
RFC 3021 defines 31-bit prefixes specifically for point-to-point router interconnects, eliminating directed broadcast and network reservations to conserve scarce IPv4 address space.