Answer to Question #319465 in Computer Networks for Madhu

Question

An organization is granted a block of addresses with the beginning address

70.10.27.0/28. The organization needs to have 3 subblocks of addresses to use in its three

subnets: Use VLSM. Design the network and plot it completely with respective subnets, IP

range, Network IDs .

Answer 1

There are $2^{32 -24} =256$ addresses in this block. the first address is 70.10.27.0/28; The last address is 70.10.27.255/28.

To satisfy the third requirement ,we assign addresses to sub blocks, starting with the the largest and ending with the smallest one.

1) The number of addresses in the largest sub block ,which requires 120 addresses, is not power of 2, we allocate 128 addresses .The subnet mask for this subnet can be found as 32 -log₂128 =25. The first address in this block is 70.10.27.0/25 ; the last address is 70.10.27.127/25.

2)The number of addresses in the second largest sub block , which requires 60 addresses , is not a power of 2 either, we allocate 64 addresses .The subnet mask for this subnet can be found as $32 - log_{2}64 = 26$ .The first address in this block is 70.10.27.128/26;The last address is 70.10.27.191/26.

3) The number of addresses in the smallest sub block ,which requires 10 addresses, is not a power of 2 either we allocate 16 addresses. The subnet mask for this subnet can be found as $32-log_{2}16 = 28$ . The first address in this block is 70.10.27.192/28; The last address is 70.10.27.207/28.