CCNA IP Routing Practice Question
Which summary route best represents these four networks?
10.20.0.0/24 10.20.1.0/24 10.20.2.0/24 10.20.3.0/24
⚠ Common exam trap
Be careful to calculate the correct subnet mask that covers all given networks without including unnecessary additional ranges.
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
✓
10.20.0.0/22
Four contiguous /24 networks starting at 10.20.0.0 summarize cleanly into 10.20.0.0/22. That block covers 10.20.0.0 through 10.20.3.255.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
10.20.0.0/22
Why this is correct
10.20.0.0/22 is the correct summary because it aggregates exactly the four /24 networks 10.20.0.0, 10.20.1.0, 10.20.2.0, and 10.20.3.0 into a single contiguous block. The /22 prefix length means the first 22 bits are fixed, covering address space from 10.20.0.0 to 10.20.3.255, which is a power-of-two boundary and the smallest supernet that contains all four without any wasted addresses.
- ✗
10.20.0.0/23
Why it's wrong here
10.20.0.0/23 is incorrect because that prefix length yields a block of 512 addresses, equal to exactly two /24 subnets: 10.20.0.0 through 10.20.1.255. It cannot encompass the four fully populated /24 networks listed because the equivalent address space of four /24s requires 1024 addresses, which exceeds what a /23 can cover.
When this WOULD be correct
If the question asked for a summary route that only included the first two networks (10.20.0.0/24 and 10.20.1.0/24), then 10.20.0.0/23 would be the correct answer, as it would effectively summarize those two networks.
- ✗
10.20.0.0/24
Why it's wrong here
10.20.0.0/24 is incorrect because it represents only the single subnet 10.20.0.0 through 10.20.0.255. This covers just the first of the four listed networks, completely ignoring 10.20.1.0/24, 10.20.2.0/24, and 10.20.3.0/24, so it fails to summarize the required range.
When this WOULD be correct
In a different question where only the network 10.20.0.0/24 is being considered for summarization, such as when asked to identify the route for a single subnet, option C would be the correct answer.
- ✗
10.20.0.0/21
Why it's wrong here
10.20.0.0/21 is wrong because it summarizes a much larger block: 10.20.0.0 through 10.20.7.255, which includes eight /24 subnets. Although it does contain the four desired networks, it also aggregates 10.20.4.0/24 through 10.20.7.0/24, thereby advertising routes for networks that do not exist and potentially causing suboptimal routing or black-holing.
When this WOULD be correct
In a different scenario where the question asks for a summary route that includes not only the four specified networks but also additional networks such as 10.20.4.0/24 and 10.20.5.0/24, then 10.20.0.0/21 would be the correct answer as it would cover all those networks.
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.
✓10.20.0.0/22Correct answer▾
Why this is correct
10.20.0.0/22 is the correct summary because it aggregates exactly the four /24 networks 10.20.0.0, 10.20.1.0, 10.20.2.0, and 10.20.3.0 into a single contiguous block. The /22 prefix length means the first 22 bits are fixed, covering address space from 10.20.0.0 to 10.20.3.255, which is a power-of-two boundary and the smallest supernet that contains all four without any wasted addresses.
✗10.20.0.0/23Wrong answer — click to see why▾
Why this is wrong here
Option B, 10.20.0.0/23, is incorrect because it only encompasses two of the four specified networks (10.20.0.0/24 and 10.20.1.0/24), failing to include the other two networks (10.20.2.0/24 and 10.20.3.0/24).
★ When this WOULD be the correct answer
If the question asked for a summary route that only included the first two networks (10.20.0.0/24 and 10.20.1.0/24), then 10.20.0.0/23 would be the correct answer, as it would effectively summarize those two networks.
Why candidates choose this
Candidates might choose this option because they recognize that 10.20.0.0/23 covers multiple subnets, leading them to mistakenly believe it could summarize a larger range than it actually does.
✗10.20.0.0/24Wrong answer — click to see why▾
Why this is wrong here
Option C is incorrect because it only summarizes a single network (10.20.0.0/24) and does not encompass the other three networks (10.20.1.0/24, 10.20.2.0/24, 10.20.3.0/24) that need to be included in the summary route.
★ When this WOULD be the correct answer
In a different question where only the network 10.20.0.0/24 is being considered for summarization, such as when asked to identify the route for a single subnet, option C would be the correct answer.
Why candidates choose this
Candidates may choose this option because it represents a valid subnet and they might misinterpret the question as asking for the most specific route rather than a summary of multiple networks.
✗10.20.0.0/21Wrong answer — click to see why▾
Why this is wrong here
Option D (10.20.0.0/21) is incorrect because it encompasses a larger range of addresses than required, including networks that are not part of the specified four networks, which are only within the /24 range of 10.20.0.0 to 10.20.3.0.
★ When this WOULD be the correct answer
In a different scenario where the question asks for a summary route that includes not only the four specified networks but also additional networks such as 10.20.4.0/24 and 10.20.5.0/24, then 10.20.0.0/21 would be the correct answer as it would cover all those networks.
Why candidates choose this
Candidates may find this option tempting because it appears to provide a broader summary, which can seem advantageous in scenarios where summarization is desired, leading to a misunderstanding of the specific address range required.
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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JA
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.