ISP address allocation from 190.100.0.0/16

Total block = 2^16 = 65,536 addresses. Allocate the largest subblocks first (aligned on their size) so that blocks stay contiguous and aligned.

Group 1: 64 customers, 256 addresses each

• 256 = 2^8 → host bits = 8 → mask /24 per customer.
• Total = 64 × 256 = 16,384 addresses (= a /18 block).
• Range: 190.100.0.0 – 190.100.63.255

Customer	Block
1	190.100.0.0/24
2	190.100.1.0/24
...	...
64	190.100.63.0/24

Group 2: 128 customers, 128 addresses each

• 128 = 2^7 → host bits = 7 → mask /25 per customer.
• Total = 128 × 128 = 16,384 addresses (a /18 block).
• Starts right after group 1: 190.100.64.0 – 190.100.127.255

Customer	Block
1	190.100.64.0/25
2	190.100.64.128/25
3	190.100.65.0/25
...	...
128	190.100.127.128/25

Group 3: 128 customers, 64 addresses each

• 64 = 2^6 → host bits = 6 → mask /26 per customer.
• Total = 128 × 64 = 8,192 addresses (a /19 block).
• Starts right after group 2: 190.100.128.0 – 190.100.159.255

Customer	Block
1	190.100.128.0/26
2	190.100.128.64/26
3	190.100.128.128/26
4	190.100.128.192/26
5	190.100.129.0/26
...	...
128	190.100.159.192/26

Summary

Group	Customers	Each	Mask	Total	Range
1	64	256	/24	16,384	190.100.0.0 – 190.100.63.255
2	128	128	/25	16,384	190.100.64.0 – 190.100.127.255
3	128	64	/26	8,192	190.100.128.0 – 190.100.159.255

Allocated = 16,384 + 16,384 + 8,192 = 40,960

Addresses still available = 65,536 − 40,960 = 24,576

The free range is 190.100.160.0 – 190.100.255.255 (96 × 256 = 24,576), which can be split into further subblocks such as 190.100.160.0/19 and 190.100.192.0/18.