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Route Summarization Calculator

Compute the most efficient summary route (aggregate route) for a set of IP prefixes.

Summary Route

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Prefix Length

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Total Prefixes Summarized

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Details


        


      

        

          
How to use the route summarization calculator

          
    
            
  1. Paste two or more subnets that should aggregate into a single advertisement.
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  2. The tool computes the longest common prefix that contains all inputs.
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  3. Verify the summary does not absorb networks you did not intend to attract.
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Frequently asked questions

          

            

              What is the difference between summarization and aggregation?
              
Both terms describe combining multiple specific routes into a single shorter advertisement. CCNA material uses 'summarization' inside an AS; BGP material uses 'aggregation' between ASes.

            

            

              Why does summarizing reduce routing table churn?
              
A summary route stays stable even if one of its specific subnets flaps. Neighbours never see the flap, which protects the rest of the network from convergence cycles.

            

            

              When does summarization cause black-hole routing?
              
If the summary covers addresses that are not actually reachable through this router, traffic to those addresses lands on the wrong device and is dropped.

            

            

              How do you choose the longest common prefix?
              
Convert the boundary addresses to binary and walk left-to-right until the bits diverge. The number of matching bits is the longest common prefix length.