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VLANlab
Calculators
16 tools
Subnet CalculatorCIDR Range ViewerVLSM CalculatorCloudVLAN PlannerBandwidth CalcIPv6 Subnet CalcIP ↔ BinarySupernet CalcCIDR MergeCIDR to IP RangeCIDR SplitIPv4 → IPv6CIDR OverlapFree IP Space FinderDHCP CalculatorMTU Calculator
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What Is My IP?IPv6 TestSpeed TestHTTP Request Headers
DNS LookupDNS PropagationDNS Health CheckerSPF AnalyzerPTR LookupCAA RecordSRV RecordDNS TraceDNS PrivacyDANE / TLSADNSSEC CheckerSPF BuilderDKIM GeneratorZone DiffPTR Zone Generator
Subnet CalculatorCIDR Range ViewerVLSM CalculatorVLAN PlannerBandwidth CalcIPv6 Subnet CalcIP ↔ BinarySupernet CalcCIDR MergeCIDR to IP RangeCIDR SplitIPv4 → IPv6CIDR OverlapFree IP Space FinderDHCP CalculatorMTU Calculator
WHOIS LookupDomain Age CheckerSubdomain FinderIP GeolocationASN / BGP LookupIP Blacklist CheckReverse IP LookupMAC Address LookupBGP Prefix LookupRPKI / ROA CheckDomain Availability
Email InspectorDKIM CheckerEmail HeadersSMTP Test
SMTP TLS CheckSoon
MX Health CheckEmail SecurityDMARC Generator
Temp MailSoon
Is It Down?SSL/TLS CheckerOpen Port CheckerOG Tag CheckerOCSP CheckerPing / LatencyHTTP InspectorRedirect ChainCSP AnalyzerTech Stack CheckerBetaTracerouteBetaHTTP/2 + HTTP/3robots.txt ViewerSSL Cert DecoderBanner GrabberWebSocket TesterCORS TesterHTTP TimingStructured DataPWA ManifestSEO Auditor
One-Time SecretHash GeneratorPassword StrengthSecurity.txtCT Log SearchAXFR Zone Test
HTTP Sec ScoreSoon
WebRTC Leak TestIP Reputation
JSON FormatterYAML FormatterBase64 / URL EncodeJWT DecoderRegex TesterUnix TimestampCron BuilderUUID / ULIDPunycode / IDNBase ConverterACL Generator
CSS Unit ConverterColor ToolkitGradient GeneratorcURL BuilderURL ParserURL Encoder/DecoderHTTP Status CodesBox Shadow GenFavicon GeneratorQR Code GeneratorFlex & Gridrobots.txt Tester
Text CompareCase ConverterText CleanerText AnalyzerText TransformerList ToolsLorem GeneratorSlug Generator
Cloud VPC PlannerCloud IP RangeSecurity GroupsIAM AnalyzerK8s CIDR PlannerFirewall BuilderHCL FormatterEgress Cost CalcCloud DNS Zone
VM Cost EstimatorSoon
Proxmox Net ConfigVMware Port GroupHyper-V vSwitchVXLAN VNI PlannerKVM Net ConfigXCP-ng NetworkNSX-T Segment
Disposable Email DetectorPhone InspectorTor Exit NodeVPN/Proxy DetectDomain ReputationTyposquat DetectUsername SearchFavicon Hash
GitHub ActionsDockerfile Gendocker-composeArgoCD AppK8s Manifests
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Free IP Space Finder

Find unallocated gaps in a CIDR block after accounting for allocated subnets.

Related Tools

CIDR Overlap

Detect overlapping IP address ranges between CIDR blocks. Check a single pair or scan an entire list for conflicts.

Subnet Calculator

Enter any IPv4 address and CIDR prefix or dotted subnet mask like 255.255.255.0. Network address, broadcast, host range, and wildcard mask calculate instantly. The built-in visual subnet calculator lets you split and rejoin blocks interactively.

CIDR Merge

Paste a list of IPv4 or IPv6 CIDR blocks and merge overlapping or adjacent ranges into the smallest possible set of non-overlapping prefixes.

About this tool

Free Space Finder identifies unallocated IP address gaps within a parent CIDR block. Enter the parent block (e.g. 10.0.0.0/16) and a list of already-allocated subnets. The tool merges overlapping allocations, then calculates the remaining free ranges and expresses them as CIDR blocks. The coverage bar shows allocation density at a glance. Useful for IP address management (IPAM), network planning, and auditing address utilization.