IP Subnet Calculator
Calculate network details from an IPv4 address and CIDR notation: network address, broadcast, usable host range, and number of hosts.
Inputs
Network address
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Broadcast address
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Subnet mask
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Usable host range
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Total hosts
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About IP Subnet Calculator
CIDR notation
/24 means the first 24 bits identify the network, leaving 8 bits for hosts (256 addresses, 254 usable). /16 = 65,536 addresses. /30 = 4 addresses, 2 usable (point-to-point links).
Reserved blocks
Private: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Loopback: 127.0.0.0/8. Link-local: 169.254.0.0/16. Multicast: 224.0.0.0/4. Public IPs come from RIRs.
Why -2 hosts?
Network address (all-zero host bits) identifies the subnet; broadcast (all-one host bits) reaches all hosts. Both are reserved. /31 and /32 skip these conventions for point-to-point.