CIDR Notation for Networks 10.8.16.0/22 and 10.8.31.0/21

Based on networks 10.8.16.0/22 and 10.8.31.0/21, which of the following is the BEST summarized CIDR notation?

A.

10.8.0.0/16

B.

10.8.0.0/19

C.

10.8.0.0/20

D.

10.0.0.0/24

A.

To determine the best summarized CIDR notation for the given networks, we need to find the network range of each network and then determine the common bits in the network address.

The first network 10.8.16.0/22 has a subnet mask of 255.255.252.0. This means that the network address is 10.8.16.0 and the broadcast address is 10.8.19.255. The host range is 10.8.16.1 - 10.8.19.254.

The second network 10.8.31.0/21 has a subnet mask of 255.255.248.0. This means that the network address is 10.8.24.0 and the broadcast address is 10.8.31.255. The host range is 10.8.24.1 - 10.8.31.254.

To determine the common bits in the network address, we can convert both network addresses to binary and compare them bit by bit. The first 18 bits in both network addresses are identical, which gives us a common prefix of 10.8.16.0/18.

However, we need to make sure that this prefix includes all the hosts in both networks. To do this, we can check if the broadcast address of each network falls within the common prefix. In this case, the broadcast address of the first network (10.8.19.255) is within the common prefix, but the broadcast address of the second network (10.8.31.255) is not.

Therefore, we need to expand the common prefix to include the second network's broadcast address. The first 19 bits in both network addresses are identical, which gives us a common prefix of 10.8.16.0/19. This prefix includes all the hosts in both networks, and it is the best summarized CIDR notation.

Therefore, the answer is B. 10.8.0.0/19.