IPv4 Subnet calculator
CIDR input → network address, broadcast, mask, wildcard, host range, address type. Plus binary breakdown and splitting a subnet into smaller ones.
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Calculator and breakdown
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Binary representation
blue — network bits, green — host bitsEnter a CIDR — bits will appear here.
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Split into subnets
pick a new prefix — the network splits into equal subnetsSplit into /
Enter a valid CIDR and pick a new prefix.
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About CIDR and IPv4
CIDR — prefix
Classes are legacy192.168.1.0/24 · 10.0.0.0/8
Classless Inter-Domain Routing (CIDR) replaced classes A/B/C in 1993. Prefix /24 means: the first 24 bits identify the network, the rest — hosts. Gives flexibility: you can take /27 (32 addresses) or /28 (16) without a byte-boundary constraint.
Private ranges
RFC 191810.0.0.0/8 · 172.16/12 · 192.168/16
Three ranges are reserved for internal networks: 10.0.0.0/8 (16.7M addresses), 172.16.0.0/12 (1M), 192.168.0.0/16 (65K). They aren't routable on the internet — use freely on LAN. Plus 169.254.0.0/16 — link-local (APIPA).
Broadcast and wildcard
Inverted mask255.255.255.0 → 0.0.0.255
Broadcast — the last address in a subnet, delivers a packet to every host. Wildcard — inverted mask (0-bits become 1), used in Cisco ACLs: 0 = 'must match', 1 = 'any'. For /24: mask 255.255.255.0, wildcard 0.0.0.255.
Usable hosts
N - 2/24 = 254 · /30 = 2 · /31 = 2
In a normal subnet N addresses, 2 are reserved: network and broadcast. Usable hosts = 2^(32-prefix) - 2. Exceptions: /31 (point-to-point) — 2 hosts without broadcast, /32 (single address) — 1 host.