- A
172.16.32.0/22
Correct. This is correct. A /22 beginning at 172.16.32.0 cleanly includes 172.16.32.0 through 172.16.35.255, which matches the four listed /24 networks exactly.
- B
172.16.32.0/23
Why wrong: A /23 covers only two /24 networks, not four. It would include the first half of the list but would leave out 172.16.34.0/24 and 172.16.35.0/24. This is a common mistake when candidates focus on the first two entries and forget to account for the whole range.
- C
172.16.32.0/21
Why wrong: A /21 is larger than needed. Although it would include the required routes, it would also include additional address space beyond them. Overly broad summaries can create inaccurate advertisements and make troubleshooting harder, so exam questions usually expect the smallest correct summary that cleanly fits the listed routes.
- D
172.16.34.0/22
Why wrong: The prefix length looks appealing because /22 is the right size, but the network boundary is wrong. Summary routes must start at the proper boundary for the mask length. A /22 block must begin on a multiple-of-four boundary in the third octet, which makes 172.16.32.0 valid and 172.16.34.0 invalid.
Quick Answer
The correct summary route is 172.16.32.0/22 because a /22 prefix covers exactly four consecutive /24 networks when the starting address falls on a valid boundary. In route summarization, you must align the summary address so that the network bits are identical across all subnets; here, the binary pattern of 172.16.32.0 through 172.16.35.0 shares the first 22 bits, making the /22 the smallest block that contains them all without overlapping into unintended ranges. On the CCNA 200-301 v2 exam, this concept tests your ability to perform efficient route aggregation, a key skill for reducing routing table size and controlling advertisement scope. A common trap is choosing a /23, which is too small, or a /21, which is too broad and may leak routes. Remember the memory tip: “Count the networks, then check the boundary”—for every four /24s, think /22, but only if the first network is divisible by four in the third octet.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency.. 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 network engineer must summarize the following routes before advertising them upstream:
172.16.32.0/24 172.16.33.0/24 172.16.34.0/24 172.16.35.0/24
Which summary route should be used?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
172.16.32.0/22
The correct summary is 172.16.32.0/22 because a /22 covers exactly four consecutive /24 networks when the starting boundary is aligned correctly. This is the part many people miss: summarization is not only about how many networks fit into a block, but also where that block starts. Here the four /24 networks begin neatly at 172.16.32.0 and continue through 172.16.35.255, which is the exact range a /22 covers. A /23 would be too small, while a /21 would be unnecessarily broad and could advertise addresses you do not intend to include. The /22 beginning at 172.16.34.0 is not on a valid /22 boundary, so that option is misaligned.
Key principle: Route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
172.16.32.0/22
Why this is correct
Correct. This is correct. A /22 beginning at 172.16.32.0 cleanly includes 172.16.32.0 through 172.16.35.255, which matches the four listed /24 networks exactly.
Related concept
Route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency.
- ✗
172.16.32.0/23
Why it's wrong here
A /23 covers only two /24 networks, not four. It would include the first half of the list but would leave out 172.16.34.0/24 and 172.16.35.0/24. This is a common mistake when candidates focus on the first two entries and forget to account for the whole range.
When this WOULD be correct
In a different scenario where only the first two routes (172.16.32.0/24 and 172.16.33.0/24) need to be summarized for a specific upstream connection, option B would be the correct answer as it accurately summarizes those two networks.
- ✗
172.16.32.0/21
Why it's wrong here
A /21 is larger than needed. Although it would include the required routes, it would also include additional address space beyond them. Overly broad summaries can create inaccurate advertisements and make troubleshooting harder, so exam questions usually expect the smallest correct summary that cleanly fits the listed routes.
When this WOULD be correct
In a scenario where a network engineer needs to summarize routes that include 172.16.32.0/24, 172.16.33.0/24, 172.16.34.0/24, 172.16.35.0/24, and additional routes such as 172.16.36.0/24 to 172.16.39.0/24, then 172.16.32.0/21 would be the correct summary route to encompass all those networks.
- ✗
172.16.34.0/22
Why it's wrong here
The prefix length looks appealing because /22 is the right size, but the network boundary is wrong. Summary routes must start at the proper boundary for the mask length. A /22 block must begin on a multiple-of-four boundary in the third octet, which makes 172.16.32.0 valid and 172.16.34.0 invalid.
When this WOULD be correct
In a different scenario, if the question specified that only the routes 172.16.34.0/24 and 172.16.35.0/24 needed to be summarized, then 172.16.34.0/22 would be the correct answer as it would encompass both of those subnets.
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.
✓172.16.32.0/22Correct answer▾
Why this is correct
Correct. This is correct. A /22 beginning at 172.16.32.0 cleanly includes 172.16.32.0 through 172.16.35.255, which matches the four listed /24 networks exactly.
✗172.16.32.0/23Wrong answer — click to see why▾
Why this is wrong here
Option B, 172.16.32.0/23, is incorrect because it only summarizes two of the four provided routes (172.16.32.0/24 and 172.16.33.0/24), failing to include the other two routes (172.16.34.0/24 and 172.16.35.0/24).
★ When this WOULD be the correct answer
In a different scenario where only the first two routes (172.16.32.0/24 and 172.16.33.0/24) need to be summarized for a specific upstream connection, option B would be the correct answer as it accurately summarizes those two networks.
Why candidates choose this
Candidates may be tempted by option B because it appears to summarize a contiguous block of addresses, leading them to mistakenly believe it covers all required routes.
✗172.16.32.0/21Wrong answer — click to see why▾
Why this is wrong here
Option C (172.16.32.0/21) includes a broader range of addresses than necessary, covering 172.16.32.0 to 172.16.39.255, which exceeds the specified routes and could lead to incorrect routing information being advertised.
★ When this WOULD be the correct answer
In a scenario where a network engineer needs to summarize routes that include 172.16.32.0/24, 172.16.33.0/24, 172.16.34.0/24, 172.16.35.0/24, and additional routes such as 172.16.36.0/24 to 172.16.39.0/24, then 172.16.32.0/21 would be the correct summary route to encompass all those networks.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of subnetting, believing that a larger subnet mask would always be more efficient without considering the specific address ranges that need to be summarized.
✗172.16.34.0/22Wrong answer — click to see why▾
Why this is wrong here
Option D is incorrect because the summary route 172.16.34.0/22 would only cover the addresses from 172.16.34.0 to 172.16.35.255, missing the routes 172.16.32.0/24 and 172.16.33.0/24.
★ When this WOULD be the correct answer
In a different scenario, if the question specified that only the routes 172.16.34.0/24 and 172.16.35.0/24 needed to be summarized, then 172.16.34.0/22 would be the correct answer as it would encompass both of those subnets.
Why candidates choose this
Candidates may find option D tempting because it appears to summarize a contiguous block of addresses, leading them to believe it could be a valid summarization without considering all specified routes.
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
Ensure the summary route starts on the correct boundary and covers exactly the intended range without including extra networks.
Detailed technical explanation
How to think about this question
Route summarization is a technique used in IP routing to combine multiple contiguous networks into a single advertisement, reducing the size of routing tables and improving routing efficiency. In IPv4, summarization works by finding a common prefix that covers all the individual networks. The prefix length (subnet mask) determines how many addresses are included in the summary. For example, a /22 prefix covers 1024 addresses, or four contiguous /24 networks. To create a valid summary route, the starting address must align with the subnet mask boundary. For a /22 mask, the third octet must be a multiple of 4 because each /22 block covers four /24 networks. In this question, the four /24 networks 172.16.32.0/24 through 172.16.35.0/24 fit perfectly into the 172.16.32.0/22 summary. Choosing a smaller mask like /23 would exclude some networks, while a larger mask like /21 would include unnecessary addresses. A common exam trap is misaligning the summary route with the subnet boundary, such as using 172.16.34.0/22, which is invalid because 34 is not a multiple of 4. This misalignment causes incorrect routing advertisements and can lead to routing loops or blackholes. Practically, Cisco routers require proper alignment for summarization to work correctly, making the correct boundary critical for both exam and real-world network design.
KKey Concepts to Remember
- Route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency.
- A summary route must start at a subnet boundary aligned with its mask length, ensuring the address is a multiple of the block size.
- A /22 subnet mask covers exactly four consecutive /24 networks, making it ideal for summarizing four contiguous /24 routes.
- Choosing a summary mask that is too small excludes some networks, while a mask that is too large includes unnecessary addresses.
- Cisco routers require proper subnet alignment for summarization to function correctly and avoid routing errors.
- Incorrect summary boundaries can cause routing loops, blackholes, or incomplete route advertisements in a network.
- The third octet in a /22 summary must be divisible by 4 to align with the subnet boundary and cover four /24 networks.
- Summarization improves routing protocol scalability by minimizing the number of routes advertised upstream.
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
Route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency..
What is the correct answer to this question?
The correct answer is: 172.16.32.0/22 — The correct summary is 172.16.32.0/22 because a /22 covers exactly four consecutive /24 networks when the starting boundary is aligned correctly. This is the part many people miss: summarization is not only about how many networks fit into a block, but also where that block starts. Here the four /24 networks begin neatly at 172.16.32.0 and continue through 172.16.35.255, which is the exact range a /22 covers. A /23 would be too small, while a /21 would be unnecessarily broad and could advertise addresses you do not intend to include. The /22 beginning at 172.16.34.0 is not on a valid /22 boundary, so that option is misaligned.
What should I do if I get this 200-301 question wrong?
Review route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Route summarization combines multiple contiguous networks into a single advertisement to reduce routing table size and improve efficiency.
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Last reviewed: May 17, 2026
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