CIDR aggregator
Paste a list of CIDR blocks, ranges or addresses to get the shortest list of blocks that covers exactly the same addresses. Duplicates and overlaps go away.
Aggregated list
Example: type your own list above.
10.0.0.0/8 192.0.2.0/24 198.51.100.0/24
- Duplicates removed
- 1
- Inside another item
- 2
How it works
Aggregating (also called route summarization) merges blocks that overlap or sit side by side. Two neighbouring /25s that line up become one /24. 10.1.0.0/16 disappears when 10.0.0.0/8 is also in the list, because the /8 already holds it.
The result covers exactly the same addresses as your list, no more and no fewer. Ranges and single addresses are merged too, then split into the fewest CIDR blocks.
A shorter list makes firewall rules, mail server allowlists and SPF records (the DNS record that lists the servers allowed to send email for your domain) easier to read and quicker to check. The smallest covering block is shorter still, but it usually claims addresses that aren't yours.
To find which items overlap and how, use the CIDR overlap check. To turn the list into firewall or server rules, use the allowlist formatter.