Routse summarization

For summarize the routes first I need to look at the least subnet.
Then I have to decide which block size to use based on whole range of subnets.
For example:
10.2.1.0/24
10.2.2.0/24
10.2.3.0/24
10.2.4.0/24
Can't use block size of 4 because then it's only 10.2.0.0 - 1.2.3.255  (10.2.4.0 won't be included).
I need to use block size - 8 - then final mask will be 255.255.255.248
10.2.0.0  255.255.255.248 - summary route

Example 2:

• 172.1.4.128/25
• 172.1.7.0/24
• 172.1.6.0/24
• 172.1.5.0/24
• 172.1.4.0/25

Do you see an octet that looks interesting to you? I do. It’s the third octet. 4, 5, 6, 7, and yes, it’s a block size of 4. So you can summarize 172.1.4.0 using a mask of 255.255.252.0, which means you will use a block size of 4 in the third octet. The IP addresses forwarded with this summary are 172.1.4.1 through 172.1.7.255.