Supernet and Route Summarization Calculator

Route summarization (supernetting) replaces many network routes with fewer, larger ones, which keeps routing tables and firewall rules short. This calculator gives two answers for a list of IPv4 networks: the single summary route — the smallest network that contains them all, with a warning about any space it covers that you did not list — and the exact aggregate, the fewest CIDR blocks that cover precisely your networks after overlaps and neighbours are merged.

How to use this tool

1. Paste the networks in CIDR form, one per line or separated by commas (a bare address counts as a /32).
2. Read the summary route and how much extra space it would advertise.
3. Use the exact aggregate where only your own space may be covered, such as BGP announcements or allow-lists.
4. Check the table of unlisted blocks before using the summary.

Formula

summary prefix = number of leading bits shared by the lowest and highest address; exact aggregate = merge overlapping/adjacent ranges, then split each into the largest aligned power-of-two blocks

A block of size 2ⁿ must start on a multiple of 2ⁿ, which is why 192.168.1.0/24 + 192.168.2.0/24 cannot become one /23 even though they are adjacent. Networks with host bits set (for example 10.1.1.5/24) are treated as their network address.

Example

192.168.0.0/24 and 192.168.1.0/24 share their first 23 bits and fill 192.168.0.0/23 exactly, so both answers are 192.168.0.0/23. 10.1.0.0/24 and 10.3.0.0/24 share only 14 bits: the summary is 10.0.0.0/14 (262,144 addresses), which covers 261,632 addresses that were not listed, while the exact aggregate stays at the 2 original routes.