IPv4 and IPv6 CIDR Planner
A 32-bit and 128-bit network calculator for exact CIDR normalization, range analysis, containment, overlap and subnet allocation. It is designed for architecture reviews, cloud address planning and change validation.
Who this Lab is for
Designed for
- Network, cloud and platform architects
- Principal engineers reviewing address plans
- Security engineers validating network-policy boundaries
Use it when
- Designing VPC, VNet, cluster or tenant address allocation
- Checking whether two proposed routes or policies overlap
- Splitting a network into consistently sized subnets
- Reviewing IPv6 range and containment behaviour
A complete run, step by step
Enter the primary CIDR
Supply an IPv4 or IPv6 address and prefix. Host bits may be present; the result normalizes them.
Compare another range
Optionally add a same-family CIDR to calculate overlap and containment.
Choose a split prefix
Use a longer prefix to calculate how many equal subnets are produced.
Audit the allocation set
Paste one allocated CIDR per line to verify every range against the primary network before approval.
What you will need
Prepare the following information before starting. Use measured evidence where possible; defaults are examples and should not be treated as recommendations.
Primary CIDR
Canonical IPv4 or IPv6 address with prefix length.
Comparison CIDR
Optional same-family network for overlap and containment analysis.
Split prefix
Optional longer prefix. The planner reports the exact subnet count and previews the first 64 networks.
Allocated CIDRs
Optional allocation set, one CIDR per line. Audits alignment, containment, duplicates, overlaps and exact coverage within the primary network.
What the result tells you
Your report includes
- Canonical network and prefix
- Exact first, last, usable and total address ranges
- Same-family overlap and bidirectional containment
- Exact subnet count with a bounded allocation preview
- Batch allocation containment, alignment, overlap and exact coverage audit
How it is determined
Addresses are converted to unsigned 32-bit or 128-bit integers. Masks, network boundaries, ranges, overlap and subnet offsets are computed using bit operations. IPv4 /31 and /32 semantics are handled separately from traditional network/broadcast ranges.
Network, mask, range, containment and subnet results are integer bit operations over 32-bit IPv4 or 128-bit IPv6 values.
Model assumptions
- • IPv4 input uses canonical decimal octets.
- • IPv4 usable-host counts exclude network and broadcast for prefixes /0 through /30; /31 and /32 follow point-to-point and host-route semantics.
- • IPv6 has no broadcast address, so every address remains in the reported range.
Normalize and divide 10.42.16.7/20
Situation
The supplied address contains host bits and must be divided into /24 networks while checking overlap with 10.42.24.0/21.
Result
The canonical network is 10.42.16.0/20, it contains 4,096 addresses, overlaps the comparison network and produces exactly sixteen /24 networks.
Use the result with engineering judgement
- The planner calculates address mathematics, not provider-specific quota or routing behaviour.
- IPv4 usable-host output follows traditional network/broadcast exclusion for /0 through /30.
- Subnet previews stop after 64 rows even though the total count remains exact.
Questions before you begin
Does it support IPv6?
Yes. IPv6 calculations use the full 128-bit address and RFC-style compressed output.
Does overlap mean traffic can route between networks?
No. It only establishes mathematical range intersection. Route tables, policy and connectivity are separate.
Why reject unusual IPv4 notation?
Canonical decimal octets avoid ambiguous legacy octal and shorthand interpretations.
Ready to run CIDR Planner?
Log in to open the full interactive workspace. Your completed result can be saved, revisited and exported as a private report.
Log in and start