IPv4 Supernet Calculator

Route aggregation replaces several IPv4 prefixes with fewer advertisements. A good summary reduces routing-table entries without claiming address space that should follow a different route, security policy, owner, or failure path.

Two useful results answer different questions. A single cover route is the shortest one CIDR block containing every submitted address. An exact aggregate set is the smallest collection of CIDR blocks that covers the submitted ranges without adding addresses between or around them.

Alignment decides whether neighboring blocks collapse cleanly. Four consecutive /24 networks beginning at 10.44.0.0 align on a /22 boundary, so they form one exact 10.44.0.0/22. Remove 10.44.2.0/24 and that same /22 still covers the outer endpoints, but it also includes 256 addresses that were not submitted.

Overlapping inputs require normalization before route counts or coverage percentages mean anything. Repeating a route, entering a subnet contained by a larger route, or supplying a host address with a prefix can inflate declared addresses without adding unique coverage. Adjacent and overlapping ranges are therefore merged before exact aggregation.

Summarization is not an authorization check. The arithmetic cannot prove route ownership, reachability, next-hop consistency, firewall intent, or that all covered prefixes share the same operational fate. An exposed gap may be harmless when it is assigned to the same site and policy, or dangerous when it belongs to another tenant or more-specific route.

Before advertising a summary, compare the proposed cover with the source of truth for address allocation and routing policy. Also check for more-specific routes: longest-prefix matching can preserve a different path for part of the cover, but relying on that behavior without documenting it can make later route changes unsafe.

How to Use This Tool:

Collect the complete set of ranges that are candidates for the same routing decision, then choose whether one route or zero added coverage is the priority.

1. Paste, type, or load IPv4 routes. CIDR prefixes, slash forms with contiguous dotted masks, and address-plus-mask lines may be mixed; comments beginning with # are ignored.
2. Choose Smallest single covering route for a one-route goal or Exact aggregate route set to stay inside submitted coverage.
3. Set Allow cover route with warning when exposed addresses are acceptable for review, or Require exact coverage to block a one-route recommendation whenever exposure exists.
4. Review Route decision first, especially the cover route, exact route count, unique coverage, and exposed addresses. Correct any line-level validation error before interpreting the plan.
5. Verify Input ledger normalization and the Gap ledger against IP address management and routing records before advertising a summary.

Interpreting Results:

Exact means the single cover contains no addresses outside the merged input coverage. Review means exposure exists but the chosen goal or warning policy still allows comparison. Blocked appears only when the one-route goal is combined with strict exposure policy and the cover adds at least one address.

• Exposed addresses equal cover size minus unique submitted coverage. Zero is the only value that makes the single cover exact.
• Cover utilization is unique coverage divided by cover size. A high percentage can still hide a consequential gap, so inspect the actual CIDRs rather than relying on the percentage alone.
• Duplicate addresses measure overlap among submitted ranges. They do not add unique coverage and may indicate redundant or nested source entries.
• Selected route reduction compares the input-line count with the selected plan's route count. It is held at zero when exact representation needs at least as many routes as the input.

Technical Details:

IPv4 aggregation can be expressed as operations on inclusive integer ranges. Each CIDR line becomes an aligned network and broadcast pair. Sorting and merging those pairs establishes the unique address union before either summary plan is produced.

Formula Core

A prefix fixes the block size, which in turn fixes the normalized network and broadcast addresses.

p is prefix length, a is the entered IPv4 integer, S is block size, N is network address, B is broadcast address, and E is exposed address count. Coverage and exposure percentages divide unique and exposed counts by the cover size respectively.

Transformation Core

1. Parse each nonblank, non-comment line as an IPv4 address with a /0 through /32 prefix or a contiguous dotted mask.
2. Normalize host bits to the CIDR network boundary, sort by network and broadcast, and merge every overlapping or directly adjacent range.
3. Find the smallest aligned power-of-two block that contains the first through last merged addresses for the single cover.
4. Convert each merged range to the fewest aligned CIDR blocks for the exact aggregate set.
5. Decompose cover padding and internal gaps into CIDRs so every exposed address can be reviewed.

Declared address count is the sum of every normalized input block, including overlap. Unique address count is the size of the merged union, and their difference is duplicate coverage. Input lines are limited to 512 nonblank routes and the source text is limited to 256 KiB.

Rule Core

Address-count display formatting changes visible grouping only. It does not change normalized routes, coverage arithmetic, recommendation policy, or canonical numeric values.

Privacy and Limitations:

CIDR text and loaded route files are processed in the browser. The calculation does not query a registry, router, cloud account, or IP address management system, so operational facts must be checked separately.

• Only IPv4 addresses and contiguous masks are accepted; IPv6, wildcard masks, route metrics, next hops, and policy attributes are outside scope.
• Host bits are normalized away. Review the input ledger when an entered address was not already on its network boundary.
• Comments after # and trailing text accepted by the route forms are not part of the address calculation.
• A compact route set does not prove that aggregation is safe across ownership, security, failure-domain, or traffic-engineering boundaries.

Worked Examples:

References:

• RFC 4632: Classless Inter-Domain Routing, RFC Editor, August 2006.
• RFC 791: Internet Protocol, RFC Editor, September 1981.
• RFC 1918: Address Allocation for Private Internets, RFC Editor, February 1996.
• IPv4 Special-Purpose Address Space Registry, IANA.