IP Addressing

CIDR Aggregator

Paste a list of IPv4 networks and get the minimal CIDR blocks that cover them, or convert between an IP range and its CIDR list. Nothing is sent to any server.

redzilla.cl — cidr aggregate

Inputs

valid networks / IPs

CIDR blocks

minimal set

Addresses

covered in total

Resulting CIDR blocks

CIDR	Range (start – end)	Addresses

redzilla.cl — range → cidr

Blocks covering the range

CIDR	Range (start – end)	Addresses

Network —

Mask —

Start —

End —

Addresses —

Runs locally in your browser · no sign-up · nothing leaves your browser

How it works

The tool takes a list of IPv4 networks (in network/CIDR format or bare IPs, which count as /32) and summarizes it into the minimum set of CIDR blocks covering exactly the same addresses: it first converts each entry to a 32-bit numeric range, merges overlapping or contiguous ranges, and then applies the classic range-to-CIDR algorithm. It also converts both ways: from a start-end range to its CIDR list, and from a CIDR block to its range, mask and address count.

This process is known as route aggregation or supernetting (CIDR, RFC 4632) and it is the basis of how prefixes are announced in BGP and how routing tables and ACLs are compacted. The summary is always exact: the resulting blocks cover the same addresses as the original list, not one more, not one less.

Example: summarizing four /24s and four bare IPs

Input: 192.168.0.0/24 through 192.168.3.0/24 plus IPs 10.0.0.5, .6, .7 and .8 (eight entries).
The four /24s are contiguous and aligned, so they merge into a single block: 192.168.0.0/22 (1,024 addresses).
IPs 10.0.0.5-10.0.0.8 do not align into a single block: they become 10.0.0.5/32, 10.0.0.6/31 and 10.0.0.8/32.
Result: 8 entries reduce to 4 CIDR blocks covering exactly 1,028 addresses.

Frequently asked questions

How many /24s do I need to form a /22?

Four contiguous, aligned /24s form a /22 (1,024 addresses). In general, each bit removed from the prefix doubles the size: two aligned /24s make a /23, four make a /22 and eight make a /21. Alignment matters: 192.168.1.0/24 through 192.168.4.0/24 are also four contiguous networks, but they do not start on a /22 boundary and cannot be summarized into one exact block.

Why does my IP range produce several CIDR blocks instead of one?

A CIDR block always has a power-of-2 size and must start at an address aligned to that size. An arbitrary range such as 192.168.1.10 to 192.168.1.200 (191 addresses) meets neither condition, so it decomposes into several blocks: the tool computes the exact minimum list that covers it.

What is the difference between this exact summary and a shorter summary-address on a router?

This tool produces an exact summary: it covers the same addresses as the original list. On a router, a more aggressive summary (a shorter mask that covers extra space) is sometimes used to shrink the table further, at the risk of attracting traffic for destinations that do not exist. If you need a summary with no excess coverage, use the minimum set the tool returns.

Are the networks I paste sent to any server?

No. All parsing and aggregation run in your browser using local 32-bit arithmetic: you can paste your entire internal addressing plan and it never leaves your machine.

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Disclaimer

We take great care to keep every tool accurate and review it thoroughly; even so, we can't guarantee it is free of errors or take responsibility for how the results are used. We recommend double-checking anything critical.

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