Network Calculator

Supernetting is the reverse of subnetting: instead of carving one block into smaller pieces, you collapse several adjacent blocks into a single, shorter prefix. It's what keeps routing tables small. Rather than advertising four separate /24 routes to a neighbor, a router advertises one /22 that covers all four — fewer entries to store, fewer updates to propagate, faster convergence.

The math comes down to shared leading bits. Take the lowest network address and the highest broadcast address across all the blocks you want to summarize, then count how many high-order bits the two have in common. That count is your summary prefix length, and masking the lowest address to that prefix gives the summary network. Two adjacent /24s — 10.0.0.0/24 and 10.0.1.0/24 — span 10.0.0.0 through 10.0.1.255; those two endpoints agree on their first 23 bits, so they summarize to 10.0.0.0/23 exactly.

Summarization only aggregates cleanly when the blocks are contiguous and aligned on the right boundary. If they aren't, the smallest enclosing prefix still covers them, but it also swallows address space you didn't list. Summarize 10.0.0.0/24 and 10.0.3.0/24 and the result is 10.0.0.0/22 — which also covers 10.0.1.0/24 and 10.0.2.0/24, two blocks that weren't in your input. This calculator flags that over-cover so you don't advertise reachability for space you don't actually own or route.

Paste your blocks one per line or comma-separated, in CIDR notation. The tool reports the summary prefix plus its mask, network, broadcast, and host count, and tells you whether the aggregation is exact or over-covering. Use it when configuring route summarization on an area border or autonomous-system boundary, or just to sanity-check that a proposed supernet really does enclose the prefixes you think it does.