CIDR Summarizer

Aggregate multiple IPv4 CIDR blocks into the smallest equivalent CIDR set.

Ctrl+Enter to summarize

What is CIDR summarization?

CIDR summarization (also called aggregation or supernetting) replaces many small network blocks with fewer, larger blocks that describe exactly the same addresses. For example, four adjacent /24 networks — 10.0.0.0/24 through 10.0.3.0/24 — can be expressed as the single block 10.0.0.0/22.

Why summarize CIDR blocks?

  • Routing tables: one summary route can replace many specific routes, shrinking tables and speeding up lookup.
  • Firewall rules: fewer, larger rules are easier to read and audit — many platforms also cap the number of rules.
  • Cloud allowlists: security group and VPC peering entries are limited, so consolidating redundant entries matters.
  • Network documentation: a compact, canonical CIDR list is easier for teams to maintain than a long one with duplicates.

Aggregation vs over-permissive ranges

This tool only outputs blocks covering exactly the addresses you entered — never more. If you enter 10.0.0.0/24 and 10.0.2.0/24, it will not return 10.0.0.0/22, because that would also include 10.0.1.0/24 and 10.0.3.0/24 — addresses you did not provide. Over-permissive summarization opens firewall holes and routes traffic to networks you never intended to allow.

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