CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: a /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A host is configured with IP address 192.168.70.18/30. Which addresses belong to the same subnet block?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
192.168.70.16 through 192.168.70.19
A /30 subnet has a block size of 4. In practical terms, the relevant blocks in the last octet are 0–3, 4–7, 8–11, 12–15, 16–19, and so on. Because 18 falls inside the 16–19 block, the subnet includes network address .16, usable hosts .17 and .18, and broadcast .19.
This question checks whether you can identify the correct /30 block and understand all addresses that fall inside it.
Key principle: A /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
192.168.70.16 through 192.168.70.19
Why this is correct
This is correct because .18 belongs to the /30 block that runs from .16 to .19.
Related concept
A /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses.
✗
192.168.70.18 through 192.168.70.21
Why it's wrong here
This is wrong because /30 block boundaries do not start at .18.
When this WOULD be correct
If the question asked for the range of addresses in a /29 subnet instead of /30, then option B would be correct, as a /29 subnet allows for IP addresses from 192.168.70.16 to 192.168.70.23.
✗
192.168.70.12 through 192.168.70.15
Why it's wrong here
This is wrong because that is the previous /30 block.
When this WOULD be correct
If the question were to ask for the range of addresses in the subnet defined by a different CIDR notation, such as 192.168.70.12/30, then the range 192.168.70.12 through 192.168.70.15 would be correct, as it would represent the valid addresses in that subnet.
✗
192.168.70.20 through 192.168.70.23
Why it's wrong here
This is wrong because that is the next /30 block.
When this WOULD be correct
If the question asked for the addresses in the subnet of 192.168.70.20/30, then option D would be correct, as it would include the range from 192.168.70.20 to 192.168.70.23, which belongs to that subnet.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓192.168.70.16 through 192.168.70.19Correct answer▾
Why this is correct
This is correct because .18 belongs to the /30 block that runs from .16 to .19.
✗192.168.70.18 through 192.168.70.21Wrong answer — click to see why▾
Why this is wrong here
A /30 subnet always has a block size of 4 addresses, starting at multiples of 4. The block starting at .18 would be 192.168.70.16–.19, not .18–.21. The range .18–.21 crosses a subnet boundary and includes addresses from two different subnets.
★ When this WOULD be the correct answer
If the question asked for the range of addresses in a /29 subnet instead of /30, then option B would be correct, as a /29 subnet allows for IP addresses from 192.168.70.16 to 192.168.70.23.
Why candidates choose this
Students might think that since .18 is the host address, the subnet includes .18 and the next three addresses, not realizing that subnet boundaries are fixed at multiples of the block size.
✗192.168.70.12 through 192.168.70.15Wrong answer — click to see why▾
Why this is wrong here
The block 192.168.70.12–.15 is a different /30 subnet (network .12, broadcast .15). The host .18 belongs to the subnet .16–.19, not .12–.15.
★ When this WOULD be the correct answer
If the question were to ask for the range of addresses in the subnet defined by a different CIDR notation, such as 192.168.70.12/30, then the range 192.168.70.12 through 192.168.70.15 would be correct, as it would represent the valid addresses in that subnet.
Why candidates choose this
A student might miscalculate the block size or confuse the subnet boundaries, thinking that .18 falls into the previous block because of incorrect arithmetic.
✗192.168.70.20 through 192.168.70.23Wrong answer — click to see why▾
Why this is wrong here
The block 192.168.70.20–.23 is the next /30 subnet (network .20, broadcast .23). The host .18 is not in this range; it is in the .16–.19 subnet.
★ When this WOULD be the correct answer
If the question asked for the addresses in the subnet of 192.168.70.20/30, then option D would be correct, as it would include the range from 192.168.70.20 to 192.168.70.23, which belongs to that subnet.
Why candidates choose this
Students might incorrectly add the block size to the host address (18+4=22) and assume the subnet starts at .20, forgetting that subnet boundaries are based on the network address, not the host address.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Be careful not to confuse adjacent subnet blocks or miscalculate the block size of a /30 subnet.
Detailed technical explanation
How to think about this question
Subnetting is a fundamental concept in IP networking that divides a larger network into smaller subnetworks, or subnets, to improve routing efficiency and enhance security. A subnet mask determines the size of each subnet by specifying which portion of the IP address represents the network and which represents the host. In this question, the IP address 192.168.70.18/30 uses a subnet mask of 255.255.255.252, which means the last 2 bits of the host portion are used for host addresses, allowing for 4 IP addresses per subnet block.
The /30 subnet mask creates subnet blocks with a block size of 4 addresses, calculated as 2^(32-30) = 4. These blocks start at multiples of 4 in the last octet, such as 0, 4, 8, 12, 16, 20, and so forth. Each block includes one network address, two usable host addresses, and one broadcast address. Since 192.168.70.18 falls within the 16–19 range, the subnet block includes 192.168.70.16 (network), 192.168.70.17 and 192.168.70.18 (usable hosts), and 192.168.70.19 (broadcast).
A common exam trap is confusing the subnet boundaries or assuming the subnet starts at the host IP itself rather than the nearest multiple of the block size. This leads to incorrect subnet ranges such as 18–21 or 20–23. In practical Cisco networking, understanding subnet boundaries is crucial for configuring interfaces, ACLs, and routing protocols correctly, as misidentifying subnet ranges can cause connectivity issues or routing failures.
KKey Concepts to Remember
A /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses.
Subnet boundaries align with multiples of the block size, which is calculated as 2^(32 - subnet mask prefix).
The network address is the first IP in the subnet block and is not assignable to hosts.
The broadcast address is the last IP in the subnet block and is used to send packets to all hosts in the subnet.
Usable host addresses fall between the network and broadcast addresses and can be assigned to devices.
Cisco devices use subnet masks to determine if an IP address is local or remote for routing decisions.
Misidentifying subnet boundaries leads to incorrect network and broadcast addresses, causing connectivity issues.
Understanding subnetting is essential for configuring interfaces, ACLs, and routing protocols correctly in Cisco networks.
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.
Key takeaway
A /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review a /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — A /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses..
What is the correct answer to this question?
The correct answer is: 192.168.70.16 through 192.168.70.19 — A /30 subnet has a block size of 4. In practical terms, the relevant blocks in the last octet are 0–3, 4–7, 8–11, 12–15, 16–19, and so on. Because 18 falls inside the 16–19 block, the subnet includes network address .16, usable hosts .17 and .18, and broadcast .19.
This question checks whether you can identify the correct /30 block and understand all addresses that fall inside it.
What should I do if I get this 200-301 question wrong?
Review a /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
A /30 subnet mask creates subnet blocks of 4 IP addresses, including network, usable hosts, and broadcast addresses.
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