The figure illustrates that summarizing networks into a single address and mask can be done in three steps:

Step 1. List the networks in binary format. In the example, the two area 1 networks and are listed in binary format.

Step 2. Count the number of far left matching bits to determine the mask for the summary route. As highlighted, the first 22 far left matching bits match. This results in the prefix /22 or subnet mask

Step 3. Copy the matching bits and then add zero bits to determine the summarized network address. In this example, the matching bits with zeros at the end result in a network address of This summary address summarizes four networks:,,, and

In the example the summary address matches four networks although only two networks exist.