**An ISP is granted a block of addresses starting with 190.100.0.0/16 (65,536 addresses). The ISP
**

needs to distribute these addresses to three groups of customers as follows:

a. The first group has 64 customers; each needs 256 addresses.

b. The second group has 128 customers; each needs 128 addresses.

c. The third group has 128 customers; each needs 64 addresses.

Design the sub blocks and find out how many addresses are still available after these allocations

solution:

1. Group 1

For this group, each customer needs 256 addresses. This means that 8 (log2256) bits are

needed to define each host. The prefix length is then 32 - 8 =24. The addresses are

1st Customer:

2nd Customer:

190.100.0.0/24

190.100.1.0/24

190.100.0.255/24

190.100.1.255/24

64th Customer: 190.100.63.0/24 190.100.63.255/24

Total =64 X 256 =16,384

2. Group2

For this group, each customer needs 128 addresses. This means that 7 (10g2 128) bits are

needed to define each host. The prefix length is then 32 - 7 =25. The addresses are

1st Customer: 190.100.64.0/25

2nd Customer: 190.100.64.128/25

190.100.64.127/25

190.100.64.255/25

128th Customer: 190.100.127.128/25 190.100.127.255/25

Total =128 X 128 = 16,384

3. Group3

For this group, each customer needs 64 addresses. This means that 6 (logz 64) bits are needed

to each host. The prefix length is then 32 - 6 =26. The addresses are

SECTION 19.1 IPv4 ADDRESSES 563

1st Customer:

2nd Customer:

190.100.128.0/26

190.100.128.64/26

190.100.128.63/26

190.100.128.127/26

128th Customer: 190.100.159.192/26 190.100.159.255/26

Total =128 X 64 =8192

Number of granted addresses to the ISP: 65,536

Number of allocated addresses by the ISP: 40,960

Number of available addresses: 24,576

In this question I am not able to understand how they divide the groups