CCNA Network Infrastructure and Connectivity Practice Question
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?
⚠ Common exam trap
Ensure the summary route starts on the correct boundary and covers exactly the intended range without including extra networks.
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.
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
A /22 prefix has a block size of 4 in the third octet, so 172.16.32.0/22 spans 172.16.32.0 through 172.16.35.255, exactly covering the four /24 routes 172.16.32.0/24, 172.16.33.0/24, 172.16.34.0/24, and 172.16.35.0/24. The network address 172.16.32.0 is aligned to a multiple-of-four boundary (32 % 4 = 0), making it a valid summary. It is the smallest CIDR block that cleanly encapsulates all four contiguous subnets with no additional address space.
- ✗
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
A /22 prefix has a block size of 4 in the third octet, so 172.16.32.0/22 spans 172.16.32.0 through 172.16.35.255, exactly covering the four /24 routes 172.16.32.0/24, 172.16.33.0/24, 172.16.34.0/24, and 172.16.35.0/24. The network address 172.16.32.0 is aligned to a multiple-of-four boundary (32 % 4 = 0), making it a valid summary. It is the smallest CIDR block that cleanly encapsulates all four contiguous subnets with no additional address space.
✗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?”
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.