Network

CIDR Aggregator

IPv4 & IPv6

Merge an IP list

Paste addresses, ranges or CIDR blocks. You get the fewest blocks that cover exactly the same addresses.
Everything runs in your browser.
Working with one network? Use the subnet calculator. Need everything except a few ranges? Use the AllowedIPs calculator.

What CIDR aggregation does

Fewer blocks, exactly the same addresses

CIDR aggregation (also called summarisation or supernetting) replaces a list of networks with the fewest CIDR blocks that cover exactly the same addresses. Two neighbouring /25s become one /24, a block already inside another is dropped, and a range like 10.0.0.0 – 10.0.0.9 becomes the blocks that add up to it.

Shorter lists are easier to review and faster to apply. Cloud security groups, firewall appliances and route tables all have rule limits, and duplicates or overlaps in an allowlist often hide a mistake. The result covers exactly the input: no address is added or lost.

Aggregation
Merging adjacent or overlapping blocks into fewer, larger ones.
Overlap
Two entries that share addresses. One may sit wholly inside the other.
Host bits
A CIDR written with a host address, like 10.0.0.5/24. It is read as its network, 10.0.0.0/24.

How to use this tool

Merge and check an IP list in four steps
1
Paste your list
CIDRs, single IPs, ranges or netmask pairs, one per line or separated by commas. Comments after # are ignored.
2
Check what changed
See which entries were duplicates, which sat inside another, which ranges overlapped and which lines couldn't be read.
3
Pick an output format
A plain list, a comma-separated line, or ready-to-paste nginx, Apache, iptables or nftables rules.
4
Copy or download
The list is processed in your browser and never leaves it.

Related tools

Keep debugging with tools from the same suite
4 tools
Subnet Calculator
Calculate IP subnet ranges, network address, broadcast, subnet mask, wildcard mask and usable hosts from any CIDR notation
WireGuard AllowedIPs Calculator
Route everything through WireGuard except your LAN, an IP or any subnet: subtracts CIDR ranges and returns the exact AllowedIPs line
Subnet Mask Cheat Sheet
Printable table of every CIDR prefix from /0 to /32 with subnet mask, wildcard, addresses and usable hosts, plus private ranges and IPv6 sizes
Public IP
Display your current public IP address, location, and network information

Frequently asked questions

Common questions about merging IP lists
6 Q&A

A tool that takes a list of IP networks and returns the smallest list of CIDR blocks covering exactly the same addresses. It merges neighbours, removes duplicates and drops blocks contained in others.

No. Blocks are only merged when together they form exactly one larger block, so the output covers the same addresses as the input, no more and no fewer. The address count in the result lets you check.

Two blocks only combine when they’re aligned. 10.0.1.0/24 and 10.0.2.0/24 are adjacent, but a /23 must start on an even third octet, so they stay separate. 10.0.2.0/24 and 10.0.3.0/24 merge into 10.0.2.0/23.

CIDR (10.0.0.0/8), single addresses, ranges (10.0.0.1 - 10.0.0.50), netmask pairs (10.0.0.0 255.255.0.0) and IPv6. Separate entries with new lines, commas or semicolons. allow and deny keywords and comments after # are stripped, so you can paste an nginx block directly.

Yes. Each family is merged separately and listed IPv4 first. The iptables output uses ip6tables for IPv6, and the nftables output defines one set per family.

No. Everything runs in your browser, so internal address plans stay on your machine.