Networking - Security - Discussion

Discussion :: Security - Security (Q.No.7)

7. 

You want to create a standard access list that denies the subnet of the following host: 172.16.50.172/20. Which of the following would you start your list with?

[A]. access-list 10 deny 172.16.48.0 255.255.240.0
[B]. access-list 10 deny 172.16.0.0 0.0.255.255
[C]. access-list 10 deny 172.16.64.0 0.0.31.255
[D]. access-list 10 deny 172.16.48.0 0.0.15.255

Answer: Option D

Explanation:

First, you must know that a /20 is 255.255.240.0, which is a block size of 16 in the third octet. Counting by 16s, this makes our subnet 48 in the third octet, and the wildcard for the third octet would be 15 since the wildcard is always one less than the block size.

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