CCNA Introduction to Networks (ITN) Practice Test

To determine the smallest network mask that can accommodate 25 connected devices, it’s essential to understand how subnetting works and how to calculate the number of usable host addresses provided by different subnet masks.

A subnet mask of 255.255.255.224 indicates a /27 prefix length, which means that the first 27 bits are used for the network portion, leaving 5 bits for the host portion. The formula to calculate the number of usable host addresses in a subnet is 2^n - 2, where n is the number of bits available for hosts. In this case, n equals 5 (32 total bits - 27 network bits).

Calculating the usable addresses:

- 2^5 = 32 total addresses

- Subtracting 2 for the network and broadcast addresses gives us 30 usable addresses.

This is sufficient to connect 25 devices since the subnet can support up to 30 hosts.

Other network masks do not meet the requirement as closely. A subnet mask of 255.255.255.0 (/24) provides 256 total addresses (254 usable), which is more than necessary. The 255.255.255.128 (/25) mask offers 2^7 = 128