# CCNA Subnetting Question



## Payung (Dec 9, 2010)

http://ccnaanswers.com/wp-content/uploads/CCNA2Chapter6V4.0Answers2.jpg
Can someone explain why 84 is the correct answer for this? Thanks.

In the network shown in the graphic, three bits were borrowed from the host portion of a Class C address. How many valid host addresses will be unused on the three point-to-point links combined if VLSM is not used?
3
4
12
36
84
180


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## nbjeter3 (Aug 19, 2010)

Well the subnet mask on that would be 255.255.255.224 Which would only give you 30 usable addresses per network and 6 total networks. They weren't real clear in the question, but the assumption is that they used 3 different networks for each point to point link. I guess that would make sense, since they are using routers and can route between them. But that gives 3 networks * 30 usable hosts per network minus the 6 used for the point to point connections. 84


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## 2xg (Aug 5, 2009)

> EDUCATIONAL ASSISTANCE
> While we are happy to promote the education of users, we feel it is inappropriate to circumvent the learning process by directly assisting with assignments and projects of an educational nature. Direct answers to school or college assignments are not allowed and will not be given. However, if a user is having trouble comprehending a certain topic, the members and staff at TSF will be happy to provide assistance with understanding the topic.


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## nbjeter3 (Aug 19, 2010)

As he had already provided the correct answer and was only curious as to how the answer was derived, there was no actual breaking of the above stated rule. It was merely breaking down the way the answer was arrived at.

By breaking it down into a more simplified explanation, it only aids in his learning, and therefore no actual answer was provided that had not been provided before. 

Subnetting can get very confusing at times and everyone needs some explanation some of the time. Just wait till he reaches VLSM.. that will REALLY blow his mind. lol


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## 2xg (Aug 5, 2009)

:smile:


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