In: Computer Science
An ISP is granted a block 10.48.0.0/16. The ISP wants to allocate addresses as follows:
Group 1: 16 customers, each with 64 addresses
Group 2: 64customers, each with 16 addresses
Group 3: 16customers, each with 32 addresses.
a.Find the subnet mask, first and last addresses of 4th customer of each group.
b.Find the number of addresses available with the ISP for future customers
a) Block = 10.48.0.0/16
Group 1 : Each customer needs 64 addresses which means bits = 6 bits are needed for each host, the prefix length is : 32-6 = 26 bits. The addresses are :
Customer | First Address | Last Address |
1 | 10.48.0.0/26 | 10.48.0.63/26 |
2 | 10.48.0.64/26 | 10.48.0.127/26 |
3 | 10.48.0.128/26 | 10.48.0.191/26 |
4 | 10.48.0.192/26 | 10.48.0.255/26 |
16 | 10.48.3.192/26 | 10.48.3.255/26 |
So 4th customer of 1st group: Subnet mask : 255.255.255.192, First Address: 10.48.0.192/26, Last Address: 10.48.0.255/26
Group 2: Each customer needs 16 addresses which means = 4 bits are needed for each host, the prefix length is: 32-4 = 28 bits. The addresses are:
Customer | First Address | Last Address |
1 | 10.48.4.0/28 | 10.48.4.15/28 |
2 | 10.48.4.16/28 | 10.48.4.31/28 |
3 | 10.48.4.32/28 | 10.48.4.47/28 |
4 | 10.48.4.48/28 | 10.48.4.63/28 |
16 | 10.48.4.240/28 | 10.48.4.255/28 |
64 | 10.48.7.240/28 | 10.48.7.255/28 |
So 4th customer of 2nd group: Subnet mask : 255.255.255.240, First Address: 10.48.4.48/28, Last Address: 10.48.4.63/28
Group 3: Each customer needs 32 addresses which means = 5 bits are needed for each host, the prefix length is: 32-5 = 27 bits. The addresses are:
Customer | First Address | Last Address |
1 | 10.48.8.0/27 | 10.48.8.31/27 |
2 | 10.48.8.32/27 | 10.48.8.63/27 |
3 | 10.48.8.64/27 | 10.48.8.95/27 |
4 | 10.48.8.96/27 | 10.48.8.127/27 |
16 | 10.48.9.240/27 | 10.48.9.255/27 |
So 4th customer of 3rd group: Subnet mask : 255.255.255.224, First Address: 10.48.8.96/27, Last Address: 10.48.8.127/27
b) Number of granted addresses to the ISP: 2^16 = 65536 as the block address is 10.48.0.0/16
Number of addresses used by group 1 users: 16*64 = 1024 addresses
Number of addresses used by group 2 users: 64*16 = 1024 addresses
Number of addresses used by group 3 users: 16*32 = 512 addresses
Total number of addresses used = 1024+1024+512 = 2560 addresses
Number of available addresses = 65536 - 2560 = 62976 addresses