CIDR Aggregator
Merge IP addresses, networks and ranges into the smallest set of CIDR blocks covering exactly the same addresses.
This tool processes its input contents in your browser instead of sending them to a processing service. Page, asset and fixed usage-measurement requests are described on the Privacy page.
Summarize IPv4 and IPv6 addresses, CIDR prefixes and inclusive ranges as the smallest list of blocks with the same address coverage.
How to use it
- 1Paste one address, CIDR network or inclusive start - end range per line.
- 2Select Aggregate CIDR and review each family’s block and unique address counts.
- 3Copy the blocks or download the plain-text list.
Example
- Input
- 192.0.2.0/25 192.0.2.128/25 192.0.2.17
- Output
- 192.0.2.0/24
Both /25 networks together cover exactly 256 addresses. The single IP address was already covered.
What happens to your data
IP addresses and generated CIDR blocks stay in this tab unless you copy or download them. The aggregator makes no DNS requests.
Last updated November 2026
Shorten an address list without expanding the networks it allows. Paste IPv4 or IPv6 addresses, CIDR networks or inclusive ranges. The CIDR Aggregator removes overlaps and joins adjacent space where a larger aligned block fits. It returns the smallest set of disjoint CIDR blocks covering exactly the same addresses. Copy the result or download a plain-text list for review before applying a firewall, routing or inventory change.
How it works
Enter one address, network or range per line. A single address counts as one address. A CIDR block uses a slash followed by the number of fixed prefix bits. For an inclusive range, write two addresses with a hyphen between them. Blank lines are skipped. Both IP versions can appear in the same list, and each range must use one version throughout. IPv6 output uses lowercase hexadecimal with compressed zero runs. IPv4-mapped addresses remain IPv6 and display their embedded IPv4 address in dotted decimal.
The tool converts entries to inclusive numeric intervals and merges overlapping or immediately adjacent intervals within each IP version. It then covers every merged interval with the largest aligned block that fits at its current start, repeating until the entire interval is covered. This never fills gaps. The address counts include every covered address, including IPv4 network and broadcast addresses. They are address counts rather than estimates of usable hosts.
A CIDR network must start at its own network address. For example, 192.0.2.17/24 reports a line-specific error and suggests 192.0.2.0/24. This avoids silently broadening a host-shaped rule. Hostnames, IPv6 zone identifiers, dotted netmasks and comments are outside the input format. The form accepts up to 1,000 nonblank entries, 128,000 input characters and 10,000 output blocks. An error stops the conversion and leaves no partial list. Review address-level coverage alongside any separate rule priorities, actions, ports or protocols in your system.
Worked example: Merge adjacent halves and remove redundant entries
- Input
- 192.0.2.0/25 192.0.2.128/25 192.0.2.17
- Result
- 192.0.2.0/24
Both /25 networks together cover exactly 256 addresses. The single IP address was already covered.
Common use cases
- Consolidate an IPv4 and IPv6 allowlist before reviewing a deployment.
- Convert an inclusive IP range to the fewest aligned CIDR blocks.
- Count unique addresses across overlapping prefixes without enumerating individual addresses.
- Remove repeated addresses already covered by a larger block.
Frequently asked questions
Will aggregation add addresses outside my input?＋
The output covers exactly the same union of addresses. Separate intervals stay separate if merging would add a gap.
Can I mix IPv4 and IPv6 in one list?＋
Yes. The two address families are grouped independently, and IPv4 blocks are listed first. The endpoints of a single range need to use the same family.
Why is an address like 192.0.2.17/24 rejected?＋
The host bits are set. Use 192.0.2.0/24 to specify the whole subnet, or remove the prefix to specify just that one address.
Does the count exclude network and broadcast addresses?＋
The count includes every address in the block. Usable host counts depend on network configuration and can differ.
Can I paste a hostname or a firewall rule?＋
Paste addresses, CIDR blocks and inclusive ranges only. The tool does no DNS lookups and does not interpret rule actions, ports or priorities.
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