IPv4 IP/Subnet Checker
Check whether an IPv4 address belongs to a CIDR subnet. View the subnet mask and complete address range without confusing membership with host availability.
Compare an IPv4 address with the complete range of an aligned CIDR subnet. YES or NO describes mathematical membership only, not whether the address is available as a host.
Input
Enable JavaScript to check membership locally in your browser. The explanations remain available without JavaScript.
Results
Enter an IPv4 address and a CIDR subnet, then run the check.
- Candidate address
- Canonical CIDR subnet
- Subnet mask
- First address in the complete address range
- Last address in the complete address range
- Total number of addresses
This result describes mathematical membership in the complete address range only. It does not determine address availability, assignability or routability.
Understanding subnet membership
An address belongs to a subnet when it lies between the first and last addresses in the complete address range, including both endpoints. NO is a valid check result, not an input error.
/0 covers all 4,294,967,296 IPv4 addresses; /31 contains two addresses and /32 contains one. Both endpoints count for membership. This test does not classify the upper endpoint as an unusable broadcast or count usable hosts.
Calculations run entirely locally without sending input to a server. Membership does not establish that an address is free, assignable or routable in your network.
Frequently asked questions
What does it mean for an IPv4 address to belong to a subnet?
An address belongs to a subnet when it lies between the endpoints of its complete address range, including both endpoints. For example, 192.0.2.42 belongs to 192.0.2.0/24, while 192.0.3.42 is outside that block. NO is a valid check result, not an input error.
Does YES mean that the address is available?
No. Membership is a mathematical test; it does not inspect devices, DHCP leases or network policies. This checker does not determine whether an address is free, assignable, authorized or routable. It sends no packets or network requests to perform the calculation.
Why does the complete address range include both endpoints?
A CIDR prefix defines an address set that includes its first and last addresses. Both 192.0.2.0 and 192.0.2.255 therefore belong to 192.0.2.0/24. This check does not classify those endpoints as usable hosts or subtract two addresses from the block size.
How are /0, /31 and /32 prefixes handled?
0.0.0.0/0 contains all 4,294,967,296 IPv4 addresses. A /31 contains two addresses, while a /32 contains exactly one and has identical endpoints. All count for membership; the checker does not label the upper endpoint of a /31 as an unusable broadcast address.
Why is a CIDR such as 192.168.1.10/24 rejected?
The subnet field requires an aligned network address. For 192.168.1.10/24, the canonical network is 192.168.1.0/24. The suggestion is displayed without replacing your input: review it and enter the intended network yourself. Horizontal whitespace around / is allowed.
Which input formats and limits are supported?
Enter one plain decimal IPv4 address and one IPv4 network with an integer /0 to /32 prefix. Each field accepts at most 128 raw UTF-16 code units and surrounding whitespace. Ambiguous leading zeros, decimal masks, lists, comments, URLs, IPv6 and CIDR suffixes on the candidate address are rejected.
How is the result calculated, and can it be copied?
The address and endpoints are represented as exact integers. The test compares the candidate with the inclusive lower bound and exclusive upper bound. The copyable summary explains that comparison; if clipboard access is denied, select the text manually. Editing either input immediately invalidates the previous result.