Cisco Certified Support Technician (CCST) NetworkingNetworking FundamentalsMedium
A network engineer is designing an IPv4 addressing scheme for a new branch office that needs to accommodate 200 hosts on a single subnet. The network will use a private IP address range. Which of the following subnet masks would be most appropriate and efficient for this requirement?
- A255.255.255.224
- B255.255.255.128
- C255.255.254.0
- D255.255.255.0
Show answer & explanationAnswer & explanation
Correct answer: C. 255.255.254.0
To accommodate 200 hosts, you need a subnet that provides at least 202 usable IP addresses (200 hosts + network address + broadcast address). A /23 subnet (255.255.254.0) provides 2^(32-23) - 2 = 2^9 - 2 = 512 - 2 = 510 usable addresses, which is the smallest option that meets the requirement.
Why the other options are wrong
- A. 255.255.255.224 (/27) provides 30 usable hosts, which is insufficient for 200 hosts.
- B. 255.255.255.128 (/25) provides 126 usable hosts, which is insufficient for 200 hosts.
- D. 255.255.255.0 (/24) provides 254 usable hosts, which is enough for 200 hosts.
IPv4 Subnet Mask Calculation
Subnet mask calculation determines the number of hosts and subnets available within a given IP address range by dividing the network.
- The number of usable hosts is 2^n - 2, where 'n' is the number of host bits.
- A smaller subnet mask (fewer bits for network portion) means more hosts per subnet.
- Efficiency involves choosing a mask that meets host requirements with minimal wasted addresses.
Memory trick: Host Need = Bits Borrowed for Mask.