Check the address.
Confirm the range.
Compare an IPv4 address with a CIDR block. Membership does not establish reachability or permission.
Address and block
01 / INPUTSMembership result
02 / RESULTSRange check summary
Inside the block.
Then check the policy.
An IP address belongs to the CIDR block when it falls between the block’s first and last addresses, inclusive.
Network and broadcast addresses count as members
For /0–/30, the first and last addresses belong to the block but are excluded from the conventional host range. Cloud reservations, special-use ranges and existing allocations can further restrict assignment.
/31 and /32
A /31 is interpreted as two endpoints on a supported RFC 3021 point-to-point link, with no subnet-directed broadcast. A /32 contains one address, commonly a host route or loopback.
What membership does not prove
This check does not inspect routes, NAT, firewall policy, DNS, address ownership or connectivity. It accepts IPv4 only. For subnet masks and address counts, use the Subnet / CIDR Calculator.