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Overview

In this short blog post we are going to present a simple procedure for IPv4 prefix summarization. The procedure is based on the one found in “Optimal Routing Design” book by Russ White, Don Slice and Alvaro Retana, but differs in some respects. The process is three step, and require the use of Windows calculator for ease of computation. No binary breakdowns are involved, just some basic arithmetic. For the sake of simplicity, we skip all proofs, as those are trivial. The same approach could be adopted for use with IPv6 prefixes, provided that decimal arithmetic is replaced with hexadecimal.

Scenario

We are going to use an example to demonstrate the method. Here is the task: find the optimal (longest prefix length) summary prefix for the following set of subnets:

```192.168.100.0/22
192.168.101.0/24
192.168.99.0/24
192.168.102.0/24
192.168.105.0/24
192.168.98.0/23
```

This example is taken from the wikipedia article: http://en.wikipedia.org/wiki/Supernet that illustrates the use of binary breakdown for the purpose of address summarization.
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