Cisco Certified Support Technician (CCST) NetworkingNetworking FundamentalsHard
A network engineer is designing an IPv4 addressing scheme for a new subnet that needs to accommodate 100 host devices. Which of the following subnet masks would provide enough usable IP addresses for these hosts while minimizing wasted addresses?
- A255.255.255.128
- B255.255.255.224
- C255.255.255.0
- D255.255.255.192
Show answer & explanationAnswer & explanation
Correct answer: A. 255.255.255.128
A subnet mask of 255.255.255.128 (a /25 network) provides 2^7 - 2 = 126 usable host addresses. This is the smallest subnet that can accommodate 100 hosts, minimizing wasted addresses. 255.255.255.0 provides 254, 255.255.255.192 provides 62, and 255.255.255.224 provides 30.
Why the other options are wrong
- B. 255.255.255.224 provides 30 usable addresses, which is not enough for 100 hosts.
- C. 255.255.255.0 provides 254 usable addresses, which is too many for 100 hosts and wastes addresses.
- D. 255.255.255.192 provides 62 usable addresses, which is not enough for 100 hosts.
IPv4 Subnetting
The process of dividing a large IP network into smaller, more manageable subnetworks, improving efficiency, security, and reducing broadcast traffic.
- Uses a subnet mask to differentiate network and host portions of an IP address.
- Number of usable hosts = 2^h - 2, where 'h' is the number of host bits.
- Subnetting helps conserve IP addresses and manage network traffic.
Memory trick: Count the hosts, find the mask.