Quick Answer
The answer is 10.20.0.0/22. This summary route is correct because the four contiguous /24 networks—10.20.0.0, 10.20.1.0, 10.20.2.0, and 10.20.3.0—share the first 22 bits of their network addresses, as seen when you convert the third octet to binary: 0 (00000000), 1 (00000001), 2 (00000010), and 3 (00000011) all match in the first six bits, leaving two host bits for the block size of four. On the CCNA 200-301 v2 exam, route summarization calculation questions test your ability to identify the smallest prefix that covers a set of subnets without including extra networks; a common trap is choosing a /21 or /23, which either over-summarizes or misses addresses. To avoid this, remember the memory tip: “Count the networks as powers of two—four networks need a block size of 4, so subtract 2 from the /24 to get /22.”
This 200-301 practice question tests your understanding of ip routing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: subnet summarization aggregates multiple contiguous networks into a single route 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.
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
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
10.20.0.0/22
Correct. /22 is the smallest summary that covers exactly those four /24 networks.
10.20.0.0/23
Why wrong: /23 would cover only two /24 networks at a time.
10.20.0.0/24
Why wrong: /24 covers only one of the listed networks.
10.20.0.0/21
Why wrong: /21 would also include additional networks and is less precise than needed.
Answer choices
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.
Key principle: Subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency.
Answer analysis
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
Correct. /22 is the smallest summary that covers exactly those four /24 networks.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency.
10.20.0.0/23
Why it's wrong here
/23 would cover only two /24 networks at a time.
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
/24 covers only one of the listed networks.
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
/21 would also include additional networks and is less precise than needed.
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
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.
Why this is correct
Correct. /22 is the smallest summary that covers exactly those four /24 networks.
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.
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.
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?”
Common exam traps
Be careful to calculate the correct subnet mask that covers all given networks without including unnecessary additional ranges.
Detailed technical explanation
Subnet summarization is a critical concept in IP routing that reduces the size of routing tables by aggregating multiple contiguous networks into a single summary route. This process improves routing efficiency and conserves router resources by advertising fewer routes. In Cisco networking, summarization is often applied to contiguous subnets that share the same higher-order bits in their network addresses. To determine the correct summary route for multiple /24 networks, you analyze the binary representation of their network addresses to find the smallest subnet mask that encompasses all the given networks without including unrelated addresses. For the networks 10.20.0.0/24 through 10.20.3.0/24, the first 22 bits are common, making 10.20.0.0/22 the precise summary. This /22 mask covers exactly the IP range from 10.20.0.0 to 10.20.3.255, including all four /24 networks. A common exam trap is selecting a summary route that is either too narrow or too broad. For example, choosing 10.20.0.0/23 only covers two /24 networks, missing half the range, while 10.20.0.0/21 covers eight /24 networks, including four not listed, which can cause routing inefficiencies or incorrect traffic forwarding. Understanding how to calculate the correct summary mask ensures accurate and efficient routing in Cisco environments.
Key takeaway
Subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency.
Real-world example
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. Subnet summarization aggregates multiple contiguous networks into a single route 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
Review subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
IP Routing — This question tests IP Routing — Subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency..
The correct answer is: 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.
Review subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency., then practise related 200-301 questions on the same topic to reinforce the concept.
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency.
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Last reviewed: May 17, 2026
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