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Question number 2

Can some one explain how the answer is D for above question.

I did study summarization but i am not clear on this question. Please explain.
NetworkingRoutersNetworking Hardware-Other

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8/22/2022 - Mon
Don Johnston

First, when summarizing, the mask boundary is moved left, not right.

Of the four network in Phoenix, start with the lowest (

If the mask is moved 1 bit to the left (, that summary route will include the and the networks. Or put another way, we now have a "summary field" (as opposed to a subnet field) of 1 bit. A 1-bit summary field includes two networks.

Moving the boundary one more bit (, will create a summary route that includes the,, and networks. Or now we have a two-bit summary field which will allow 4 networks to be summarized.

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Thanks. Let me go thorough your notes.

hi Akinsd,

i understand the notes. I still have few things need to be cleared. How would I able to do the following summarization question.


question 9 , i did apply the same method but not able to understand why the answer is B and D. Please explain.
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William Peck
Don Johnston

You would need to look at the existing networks.

Core-Marketing  (2 hosts: -
Core-Sales  (2 hosts: -
Core-Admin  (2 hosts: -
Marketing LAN: (30 hosts: ( -
Sales LAN: (30 hosts: ( -
Admin LAN: (30 hosts: ( -

So for Network A, a mask of /25 is needed to have host field large enough to accommodate the 120 hosts on the LAN.

For the link, a /30 mask is used.  Answer D works and the addresses - would be assigned to the router interfaces.

Answer E would have addresses which have already been assigned to Marketing LAN.

Answer F would have addresses which have already been assigned to Admin LAN.

sorry i mean to say question 9. Please look at the question 9 about summarization.

i am not quite sure how reverse route summarization works.
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Don Johnston

I think you're overthinking that one. :-)

Look at it like you would a regular subnetting question.

What are the valid addresses for the network? -

Any addresses in that range would be your answers.

question is /20 but how come they are using /22 in the answer?

this is where i am having confusion.
Don Johnston

The /20 is a summary route which contains a number of smaller networks. Just like would be a summary for the,,,, etc.
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Thanks for the points and feedback.
Let me know if you still need help or clarification