How to Do Route Summarization

Step 1 - List all routes that need to be summarized in dotted decimal format in order of lowest to highest. Also list their matching subnet broadcast addresses.

Example Networks,,,

Subnet ID    Broadcast ID

Step 2 - Write down the the network ID of the smallest Network and write down the broadcast of the largest network. &

Step 3 - Determine the starting subnet mask

Take the existing subnet mask and subtract 1 as the starting point

24 -1 equals 23

Step 4 - Take the lowest subordinate subnet ID and find the network ID and broadcast with the defined mask from Step 3

network /23 - broadcast

( /23 does not work because it does not include all Subnet ID defined in Step 1 )

Step 3 & 4 Repeat - Subtract one more from the Subnet Mask

/23 -1 = /22

Recalculate the network and broadcast

network - broadcast

WINNER - this subnet mask successfully summarized all subnets listed in Step one and therefor is the answer!