Route Summary Calculator
Summarize networks and identify included gaps.
Route Summary Calculator: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
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Remove specified addresses and ranges.
How Route Summary Calculator Works?
This tool works by computing the single summary prefix for a set of routes and listing every gap the summary covers that no original route covers.
Enter the routes
Type the routes to combine, such as
10.1.0.0/24,10.1.1.0/24, and10.1.3.0/24.Compute the summary
The calculator finds the covering prefix:
10.1.0.0/22.Find included gaps
The summary minus the routes leaves
10.1.2.0/24.Report the trade-off
The output shows the routes saved and the addresses attracted with no real destination.
Route Summary Calculator Formula
The formula is Summary = smallest covering prefix of all routes, and Gaps = Summary − ∪ Routes.
Summary prefix
p = 32 − bitlength(MinStart XOR MaxEnd)Shared leading bits.
Gaps
Summary − ∪ RoutesAddresses inside the summary with no specific route.
Routes saved
n − 1n routes become 1.
Gap share
|Gaps| ÷ |Summary| × 100 %Accuracy cost of the summary.
Worked example: 10.1.0.0/24, 10.1.1.0/24, 10.1.3.0/24
Summary = 10.1.0.0/22 Gaps = 10.1.2.0/24 Routes saved = 2 Gap share = 256 ÷ 1,024 = 25 %
Route Summary Calculator Conversion Table
The table summarizes 6 route sets and lists the gaps each summary pulls in.
| Routes | Summary | Included Gaps | Gap Share |
|---|---|---|---|
| 10.1.0.0/24, 10.1.1.0/24, 10.1.3.0/24 | 10.1.0.0/22 | 10.1.2.0/24 | 25.0 % |
| 10.2.0.0/24, 10.2.1.0/24, 10.2.2.0/24, 10.2.3.0/24 | 10.2.0.0/22 | None | 0.0 % |
| 172.16.8.0/24, 172.16.10.0/24 | 172.16.8.0/22 | 172.16.9.0/24, 172.16.11.0/24 | 50.0 % |
| 192.168.16.0/22, 192.168.20.0/22, 192.168.28.0/22 | 192.168.16.0/20 | 192.168.24.0/22 | 25.0 % |
| 10.50.0.0/16, 10.51.0.0/16 | 10.50.0.0/15 | None | 0.0 % |
| 203.0.113.0/27, 203.0.113.96/27 | 203.0.113.0/25 | 203.0.113.32/27, 203.0.113.64/27 | 50.0 % |
What is Route Summary Calculator?
The Route Summary Calculator is a tool that summarizes a set of routes into 1 prefix and shows exactly which unrouted addresses the summary includes.
Summarization reduces routing table size and limits the spread of route changes. The cost is accuracy: a summary attracts traffic for every address it covers, including gaps with no real network behind them. That traffic is dropped at the summarizing router or loops between routers.
Listing the gaps makes the trade-off explicit. A Null0 or discard route for each gap prevents loops.
What are the uses of Route Summary Calculator?
There are 4 main uses of the Route Summary Calculator, including OSPF area summaries, BGP aggregates, and loop prevention.
Configuring OSPF area summaries
area 1 range 10.1.0.0 255.255.252.0advertises 1 route for the area.Creating BGP aggregates
aggregate-addressstatements announce the summary to peers.Preventing routing loops
Gaps get discard routes so traffic to them stops at the edge.
Evaluating summary quality
A high gap share signals that a different grouping fits better.