Question

An organization is granted the block 16.0.0.0/8. The administrator wants to create 500 fixed- length subnets. I) find the subnet mask. (ii) find the number of addresses in each subnet. (iii) find the first and last address in first subnet and in the last subnet.

Answer 1

Answer:

Explanation:

An organization is granted the block 16.0.0.0/8. The administrator wants to create 500 fixed- length subnets

• subnet mask -> 255.255.128.0

• The number of addresses in each subnet -> 2¹⁵ - 2 = 32768 - 2 = 32766

• first and last address in the first subnet :-

First Valid Address : 16.0.0.1

Last Valid Address : 16.0.127.254

Subnet last subnet IP is 16.249.128.0 -> 16.249.128.17

Answer 2

Answer:

(i) Mask = /17

(ii) 32,768 addresses per subnet.

(iii) The first address is 16.0.0.0 and the last address is 16.0.127.255 in the first subnet.

(iii) The first address is 16.249.128.0 and the last address is 16.249.255.255 in the last subnet 500.

Explanation:

(i) An administrator wants 500 fixed-length subnets, the number of subnets needs to be of power 2. Here, the number of subnets is 500, the number of extras is in the prefix length is $log_{2}s$, where s = $2^{number \ of \ extra \ 1s}$.

Now, $2^{9}$ = 512. We need 500 subnets, which means we need to add nine more extra 1s $(log_{2}500 = 8.96)$ to the site prefix.  So, the number of extra 1s is 9 and possible subnets is 512. The subnet prefix is then /17. Therefore, the subnet mask is 255.255.128.0.

(ii) The site has $2^{32 - 8} = 2^{24} = 16777216$ addresses. Each subnet has $2^{32-17} = 2^{15} = 32,768$ addresses.

(iii) As we know, "the first address is the beginning address of the block." Therefore, the first address in subnet 1 is 16.0.0.0.

To find the last address, we need to write 32,767 in base 256 (0.0.127.255) and add it to the first  address (in base 256).

First address in subnet 1 = 16.0.0.0

Number of address         =  0.0.127.255

Last address in subnet 1 =  16.0.127.255

Therefore, the last address in subnet 1 is 16.0.127.255.

(iv) Here, point to be noted that subnet 500 is the last subnet used by the organization, it is not the last possible subnet. To find the address in subnet 500, we need to add 499 × 32,768 = 16,351,232 in base 256 (0.249.228.0) to the first address in subnet 1.

First address in subnet 1       = 16.0.0.0

Number of addresses           = 0.249.128.0

First address in subnet 500 = 16.249.128.0

Now, we can calculate the last address in subnet 500.

First address in subnet 500 = 16.249.128.0

Number of addresses           = 0.0.127.255

Last address in subnet 500 = 16.249.255.255

Therefore, the first address is 16.249.128.0 and the last address is 16.249.255.255 in the last subnet 500.