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How to Calculate IP Address/ Route Summarization.

Calculating IP route summaries is similar to the same process as Static Routing. To Summarizing networks IP address or route into a single address and mask can be done in three steps. Let's use the following four networks below as an example:


Step 1: List the networks in binary format = 10101100.00010000 00000000 00000000 = 10101100.00010001.00000000.00000000 = 10101100.00010010.00000000.00000000 = 10101100.00010011.00000000.00000000

Step 2: Count from the left, the number of most matching bits to determine the subnet mask for the summary route or IP address. 

You can see from the example below that there are 12 left-most matching bits match. This is the prefix (CIDR), or subnet mask, for the summarized route or IP address: /12 or

How to Calculate IP Address/ Route Summarization

Step 3:

The third and final step is to copy the matching bits from the left and then add zero bits to determine the summarized network address. 

How to Calculate IP Address/ Route Summarization

From the example above, you can see that the matching bits with added zeros at the end give us the network address Subnet mask

Remember the four networks -,,, and - can now be summarized and advertised into a single network address and prefix

How to Calculate IP Address/ Route Summarization
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