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I am totally stumped at the explaination I found for the Level 1 Parent routes. I thought this explaination would help me understand the route summarization questions, please let me know if there is a better way!

The line that stumps me is : 209.165.200.0/24 is variably subnetted, 5 subnets,2 masks

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    What is it that you do not understand? In your example there is not much difference between the routing of 209.165.200.0/24 and that of 172.16.0.0/16.
    – Law29
    Commented May 15, 2016 at 16:03
  • @Law29 well can you explain me how to read a routing table.I tried understanding from ciscopress articles.But it just went over my head
    – Yasha
    Commented May 15, 2016 at 16:33
  • nvm got it ! Its saying that that 172.16.0.0/16 (classful address) has been subnetted into 5 subnets . And those 5 subnets combined use 3 different subnets
    – Yasha
    Commented May 15, 2016 at 17:25
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    Almost but not quite: not three different subnets but three different subnet masks. It's saying that there are 5 subnets explicitly defined, one per line, but there may be (and there are) addresses that are not in any of those defined subnets. The mask is represented by /24, /28, /30, /32, and if you look closely there are that number of different masks used. Has this answered your question?
    – Law29
    Commented May 15, 2016 at 17:35
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    Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin ♦
    Commented Aug 7, 2017 at 17:42

1 Answer 1

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The router is simply summarizing based on the default class of address the subnet happens to reside in. By default,

  • 209.165.200.224/30 summarizes to a Class C network of 209.165.200.0/24
  • 172.16.4.0/28 summarizes to a Class B network of 172.16.0.0/16

And if you were to have a 10-net address configured on your router, for example 10.20.4.0/25, it would summarize to a Class A network of 10.0.0.0/8.

Good luck in your studies.

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