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Question
An Internet Service Provider (ISPP) has the following chunk of CIDR-based IP addresses available with it: 245. 248.128.0/20. The ISP wants to give half of this chunk of addresses to Organization A, and a quarter of Organization B, while retaining the remaining with itself. Which of the following is a valid allocation of addresses to A and B?
An Internet Service Provider (ISPP) has the following chunk of CIDR-based IP addresses available with it: 245. 248.128.0/20. The ISP wants to give half of this chunk of addresses to Organization A, and a quarter of Organization B, while retaining the remaining with itself. Which of the following is a valid allocation of addresses to A and B?
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Solution
The correct option is D 245.248.136.0/21 and 245.248.128.0/22
It has 20 bit mask, so total number of hosts are 212hosts.
It wants half of the chunk to A, therefore mask of A should be 21 bits, so it will contain 211 hosts.
∴ Two choices for A
⇒ 245.248.1000 0000.0/21
245.248.1000 1000.0/21
∴ A can be assigned
⇒ 245.248.136.0/21
245.248.128.0/22
Now, one fourth needs to be assigned to B, hence its mask should be of 22 bits. But if we look at choice (b), the host in A and B are conflicting, therefore option (a) is correct.
It has 20 bit mask, so total number of hosts are 212hosts.
It wants half of the chunk to A, therefore mask of A should be 21 bits, so it will contain 211 hosts.
∴ Two choices for A
⇒ 245.248.1000 0000.0/21
245.248.1000 1000.0/21
∴ A can be assigned
⇒ 245.248.136.0/21
245.248.128.0/22
Now, one fourth needs to be assigned to B, hence its mask should be of 22 bits. But if we look at choice (b), the host in A and B are conflicting, therefore option (a) is correct.
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