Question

A network administrator has a block of IP addresses: 10.5.4.0/23. From this block of IP addresses, he created 32 subnets of the same size with a prefix of /28. He wants to determine the directed broadcast address for each subnet. He wrote down a list of possible broadcast addresses. Select the IP addresses that do not correspond to a broadcast address for any subnets he created. Choose two options.

a) 10.5.5.207

b) 10.5.5.159

c) 10.5.5.7

d) 10.5.4.78

e) 10.5.4.47

f) 10.5.4.95

Answer 1

Given IP  : 10/.5.4.0/23
Subnet mask : 255.255.127.0

Range of IP addresses: 10.5.4.1 - 10.5.5.254

For 1st IP 10.5.4.1

As there is suffix 28 i.e there is 4 subnet bits and 28 network bits

Subnet mask = 10.5.5.254

possible hosts and broad cast address.
IP host range broadcast address.
10.5.4.0 10.5.4.1 - 10.5.4.14 10.5.4.15
10.5.4.16   10.5.4.17 - 10.5.4.30   10.5.4.31
10.5.4.32   10.5.4.33 - 10.5.4.46   10.5.4.47
10.5.4.48   10.5.4.49 - 10.5.4.62   10.5.4.63
10.5.4.64   10.5.4.65 - 10.5.4.78   10.5.4.79
10.5.4.80   10.5.4.81 - 10.5.4.94   10.5.4.95
10.5.4.96   10.5.4.97 - 10.5.4.110   10.5.4.111
10.5.4.112   10.5.4.113 - 10.5.4.126   10.5.4.127
10.5.4.128   10.5.4.129 - 10.5.4.142   10.5.4.143
10.5.4.144   10.5.4.145 - 10.5.4.158   10.5.4.159
10.5.4.160   10.5.4.161 - 10.5.4.174   10.5.4.175
10.5.4.176   10.5.4.177 - 10.5.4.190   10.5.4.191
10.5.4.192   10.5.4.193 - 10.5.4.206   10.5.4.207
10.5.4.208   10.5.4.209 - 10.5.4.222   10.5.4.223
10.5.4.224   10.5.4.225 - 10.5.4.238   10.5.4.239
10.5.4.240   10.5.4.241 - 10.5.4.254   10.5.4.255

For last  IP 10.5.4.254

Network Address:

10.5.5.240

As there is suffix 28 i.e there is 4 subnet bits and 28 network bits

Subnet mask = 10.5.5.254

possible hosts and broad cast address.

10.5.5.0   10.5.5.1 - 10.5.5.14   10.5.5.15
10.5.5.16   10.5.5.17 - 10.5.5.30   10.5.5.31
10.5.5.32   10.5.5.33 - 10.5.5.46   10.5.5.47
10.5.5.48   10.5.5.49 - 10.5.5.62   10.5.5.63
10.5.5.64   10.5.5.65 - 10.5.5.78   10.5.5.79
10.5.5.80   10.5.5.81 - 10.5.5.94   10.5.5.95
10.5.5.96   10.5.5.97 - 10.5.5.110   10.5.5.111
10.5.5.112   10.5.5.113 - 10.5.5.126   10.5.5.127
10.5.5.128   10.5.5.129 - 10.5.5.142   10.5.5.143
10.5.5.144   10.5.5.145 - 10.5.5.158   10.5.5.159
10.5.5.160   10.5.5.161 - 10.5.5.174   10.5.5.175
10.5.5.176   10.5.5.177 - 10.5.5.190   10.5.5.191
10.5.5.192   10.5.5.193 - 10.5.5.206   10.5.5.207
10.5.5.208   10.5.5.209 - 10.5.5.222   10.5.5.223
10.5.5.224   10.5.5.225 - 10.5.5.238   10.5.5.239
10.5.5.240   10.5.5.241 - 10.5.5.254   10.5.5.255

As you can see

c) 10.5.5.7

d) 10.5.4.78

could not be the broadcast address.