Question

You have a network ID of 192.168.10.0 and require at least 25 host IDs for each subnet, with the largest amount of subnets available. Which subnet mask should you assign?
1. 255.255.255.192
2. 255.255.255.224
3. 255.255.255.240
4. 255.255.255.248

Answer 1

Correct Answer - Option 2 : 255.255.255.224

Host ID = 25

255.255.255.000 0000

number of bit in Host ID per subnet = ⌈log2 25 ⌉  = 5    

IP address = Network ID + Host ID

32 =  Network ID + 5

∴  Network ID = 32 - 5 = 27 

In subnet Mask, all Network ID 1's and Host ID 0's

1111 1111. 1111 1111. 1111 1111. 1110 0000 

255. 255.255.224