Route Summarization

Lessons Discussion
82

Hello Shamal

Yes absolutely. We can go through this together. The process is essentially the same. Let’s represent the first two octets in decimal and only the second two octets in binary to save space:

192.11.00000000.00000000
192.11.00000001.00000000
192.11.00000010.00000000
192.11.00000011.00000000

As you can see, in the third octet the first six bits are the same, and the seventh bit changes, so that means that the summary prefix that should be used is /22 (22 bits counting from the left). This is the same as a subnet mask of 255.255.252.0.

So the network address would be 192.11.00000000.00000000 which in decimal is 192.168.0.0. So the summary address is 192.168.0.0/22.

Now because the masks are different, you just have to confirm that the ranges in all of your networks are found within the summary range. If you examine the actual IP address ranges, you will see that all of them are included in the summary.

Eventually, if you do enough of these exercises, you will be able to calculate these summary addresses in your mind with relatively good accuracy.

I hope this has been helpful!

Laz

83

Thank you very much. I really appreciate the help

84

Hey Rene,
10.10.0.0
10.11.0.0
10.12.0.0
10.13.0.0

I converted them to binaries,
00001010
00001011
00001100
00001101

first 5 bits are common. So subnet mask is /13
10.8.0.0/13

But using your block method,

10.10.0.0
10.11.0.0
10.12.0.0
10.13.0.0

16 fits all. So, 256 - 16 = 240. which gives me,
10.8.0.0/12

So, which one is correct?

85

Hello Pamod

The block method is useful when you start off your series of networks from the beginning of your range, like when you start with 192.168.0.0/24. It’s at the beginning of the larger range of 192.168.0.0/16 for example.

If you want to use the block method for your example, you will have to do something like this:

10.0.0.0
10.1.0.0
10.2.0.0
10.3.0.0
10.4.0.0
10.5.0.0
10.6.0.0
10.7.0.0
10.8.0.0
10.9.0.0
10.10.0.0
10.11.0.0
10.12.0.0
10.13.0.0
10.14.0.0
10.15.0.0

And indeed, 16 would fit all of these. But because we’re not starting from 0.0, we can split this into two where the second half is:

10.8.0.0
10.9.0.0
10.10.0.0
10.11.0.0
10.12.0.0
10.13.0.0
10.14.0.0
10.15.0.0

And that’s 8 networks, so it’s 256 - 8 = 248 which gives /13. For the block method to work you still need an understanding of the way the networks behave when they are split into sections… Does that make sense?

I hope this has been helpful!

Laz

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