For example, if you want to summarize networks 192.168.8.0 through 192.168.15.0, first find the block size you can use. There are 8 networks so the block size of 8 can be used. The first network address in the block is 192.168.8.0. Now to find the mask of the summarized route, remember the mask used for a block of 8 – 248. You can also deduct the block size from 256 to find the mask. Since we are summarizing the third octet the subnet mask for the summary address will be 255.255.248.0.