Duplicate Allocation Checker
Find repeated addresses or overlapping allocations.
Duplicate Allocation Checker: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
Related Subnet Math & Set OperationsAll Tools
Bitwise Subnet Calculator
Show address-and-mask operations.
IP Address Offset Calculator
Add or subtract address positions.
Address Distance Calculator
Count positions between two addresses.
Subnet Boundary Checker
Check alignment to a specified prefix.
IP-in-Range Checker
Test whether an address belongs.
IP-in-Subnet Checker
Test membership within a CIDR block.
How Duplicate Allocation Checker Works?
This tool works by sorting every allocation record by start address and comparing each record with the records that follow it, flagging exact duplicates and partial overlaps.
Paste the allocation records
Enter a name and address, range, or CIDR for each record.
Normalize and sort
Each record becomes a start–end interval, sorted by start.
Compare neighbors
A record that starts before an earlier record ends conflicts with it.
Classify the conflict
Conflicts are labelled Exact duplicate, Contained, or Partial overlap.
Duplicate Allocation Checker Formula
The formula is Conflict(i, j) = (Start_j ≤ End_i) for j after i in sorted order, with an exact duplicate when Start_i = Start_j and End_i = End_j.
Conflict test
S_j ≤ E_iSorted order guarantees S_i ≤ S_j.
Exact duplicate
S_i = S_j AND E_i = E_jSame space recorded twice.
Contained
E_j ≤ E_iRecord j lies inside record i.
Partial overlap
E_j > E_iRecords share part of their space.
Worked example: 3 conflicting records
Printers-A = 10.5.1.0/26 Printers-B = 10.5.1.0/26 → Exact duplicate Servers = 10.5.2.0/24 Backup = 10.5.2.128/25 → Contained DHCP = 10.5.3.10–.200 Cameras = 10.5.3.150–.220 → Partial overlap
Duplicate Allocation Checker Conversion Table
The table lists the conflicts found among 8 allocation records.
| Record A | Record B | Conflict Type | Shared Addresses |
|---|---|---|---|
| Printers-A 10.5.1.0/26 | Printers-B 10.5.1.0/26 | Exact duplicate | 64 |
| Servers 10.5.2.0/24 | Backup 10.5.2.128/25 | Contained | 128 |
| DHCP 10.5.3.10–10.5.3.200 | Cameras 10.5.3.150–10.5.3.220 | Partial overlap | 51 |
Mgmt (10.5.4.0/27) and Voice (10.5.4.32/27) are adjacent and produce no conflict.
What is Duplicate Allocation Checker?
The Duplicate Allocation Checker is a tool that finds address allocations recorded more than once or overlapping with another allocation.
Spreadsheets and IPAM systems collect duplicates over the years: the same subnet filed under 2 names, a backup network carved inside a server network, or a camera range that bites into a DHCP pool. Each duplicate is a future address conflict.
The checker labels every conflict by type, which separates harmless double entries from real overlaps that need a fix.
What are the uses of Duplicate Allocation Checker?
There are 4 main uses of the Duplicate Allocation Checker, including IPAM cleanup, pre-migration checks, and change review.
Cleaning IPAM databases
Exact duplicates are merged and overlaps are sent to owners.
Checking before migrations
Overlapping records must be resolved before moving to a new IPAM tool.
Reviewing change requests
New allocations are tested against the full record set.
Auditing DHCP and static plans
Overlaps between pools and static ranges are caught early.