Which of the following is the correct CIDR notation for a network with a subnet mask of 255.255.255.240? 

Solution

Classless Inter-Domain Routing (CIDR) notation is a way of specifying IP addresses and their associated routing prefix. The subnet mask 255.255.255.240 corresponds to a /28 prefix length because the first 28 bits of the address are used for the network portion, and the remaining 4 bits are used for host addresses. This results in 16 total IP addresses, with 14 usable for hosts (2 are reserved for network and broadcast addresses). CIDR is commonly used to create smaller or more flexible subnets within larger address spaces. Why other options are wrong: A) /24 corresponds to a subnet mask of 255.255.255.0, which allows for 256 total IP addresses. B) /25 corresponds to a subnet mask of 255.255.255.128, which allows for 128 total IP addresses. C) /26 corresponds to a subnet mask of 255.255.255.192, which allows for 64 total IP addresses. E) /30 corresponds to a subnet mask of 255.255.255.252, which allows for only 4 total IP addresses.