Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A host uses the subnet mask 255.255.255.240. How many usable host addresses exist in each subnet?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
12
This is wrong because 12 does not match the /28 calculation.
B
Best answer
14
This is correct because a /28 has 16 total addresses minus 2 reserved equals 14 usable hosts.
C
Distractor review
16
This is wrong because 16 is the total block size, not the usable count.
D
Distractor review
30
This is wrong because 30 usable hosts corresponds to a /27 subnet.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting the total number of addresses in the subnet (16) instead of the usable host addresses (14). Candidates often forget to subtract the network and broadcast addresses, which are reserved and cannot be assigned to hosts. Another common mistake is confusing the /28 subnet mask with /27, which offers 30 usable hosts, leading to incorrect answers like 30. This confusion arises because both subnet masks are close in size but differ significantly in host capacity. Always remember that usable hosts equal total addresses minus two reserved addresses.
Technical deep dive
How to think about this question
Subnetting is a fundamental networking concept that divides a larger IP network into smaller, manageable sub-networks or subnets. The subnet mask 255.255.255.240 corresponds to a /28 prefix length, meaning the first 28 bits are fixed for network identification, and the remaining 4 bits are available for host addressing. This mask is commonly used to create multiple small subnets within a larger network, optimizing IP address allocation and improving network performance and security. The calculation of usable host addresses in a subnet follows a standard formula: 2^n - 2, where n is the number of host bits. For a /28 mask, 4 bits are available for hosts, resulting in 2^4 = 16 total addresses. Subtracting 2 addresses reserved for the network identifier and broadcast address leaves 14 usable host addresses per subnet. This rule is critical in Cisco networking and the CCNA exam to correctly design and troubleshoot IP addressing schemes. A common exam trap is confusing the total number of addresses with usable hosts. For example, 16 addresses include network and broadcast addresses, which cannot be assigned to hosts. Another frequent mistake is mixing subnet masks, such as confusing /28 with /27, which provides 30 usable hosts. Understanding the distinction between total and usable addresses and applying the correct subnet mask is essential for accurate subnetting and avoiding errors in Cisco network configurations.
KKey Concepts to Remember
- A subnet mask of 255.255.255.240 corresponds to a /28 prefix length, allocating 4 bits for host addressing in each subnet.
- The number of usable host addresses in a subnet is calculated by 2^n minus 2, where n is the number of host bits available.
- The network address and broadcast address are reserved and cannot be assigned to hosts, reducing usable host count by two.
- A /28 subnet provides 16 total IP addresses, but only 14 are usable for hosts after excluding reserved addresses.
- Confusing total addresses with usable hosts is a common subnetting mistake that leads to incorrect IP allocation.
- Subnetting helps optimize IP address usage by dividing a network into smaller subnets with appropriate host capacities.
- Cisco devices use subnet masks to determine network and host portions of an IP address for routing and forwarding decisions.
- Understanding subnet mask to CIDR conversion is essential for quick and accurate subnetting calculations on the CCNA exam.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Related practice questions
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
A subnet mask of 255.255.255.240 corresponds to a /28 prefix length, allocating 4 bits for host addressing in each subnet.
What is the correct answer to this question?
The correct answer is: 14 — The mask 255.255.255.240 corresponds to /28. In practical terms, that leaves 4 host bits, which gives 16 total addresses in each subnet. After subtracting the network and broadcast addresses, 14 usable hosts remain. This is a classic host-capacity calculation and a very common subnetting pattern on the exam.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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