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: routers use the longest prefix match rule to select the most specific route for a given destination IP address.. 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 router has routes for 10.10.0.0/16, 10.10.20.0/24, and a default route. Which route is used for destination 10.10.20.55?
The 10.10.0.0/16 route
Why wrong: The /16 matches, but it is less specific than the /24.
The default route
Why wrong: The default route is used only when no more specific route matches.
The 10.10.20.0/24 route
Correct. The /24 route is chosen.
The router load-balances across all matching routes
Why wrong: Routers do not load-balance across unrelated prefix lengths like this.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The 10.10.20.0/24 route
The destination matches multiple routes, but the /24 is the most specific match and wins by longest prefix match.
Key principle: Routers use the longest prefix match rule to select the most specific route for a given destination IP address.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The 10.10.0.0/16 route
Why it's wrong here
The /16 matches, but it is less specific than the /24.
When this WOULD be correct
In a different scenario where the 10.10.20.0/24 route is removed from the routing table, the 10.10.0.0/16 route would then be the only available route for the destination 10.10.20.55, making it the correct answer.
The default route
Why it's wrong here
The default route is used only when no more specific route matches.
When this WOULD be correct
If the question stated that the router only had a default route configured and no other specific routes for the 10.10.20.0/24 subnet, then the default route would be the only option available for reaching 10.10.20.55.
The 10.10.20.0/24 route
Why this is correct
Correct. The /24 route is chosen.
Related concept
Routers use the longest prefix match rule to select the most specific route for a given destination IP address.
The router load-balances across all matching routes
Why it's wrong here
Routers do not load-balance across unrelated prefix lengths like this.
When this WOULD be correct
In a scenario where the router is configured with multiple equal-cost paths to the same destination, such as 10.10.20.0/24 and another route with the same prefix length, a question could ask which routes would be used for load balancing. In that case, the answer would be that the router load-balances across all matching routes.
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. The /24 route is chosen.
Why this is wrong here
The 10.10.0.0/16 route is broader and encompasses the 10.10.20.0/24 subnet, but it is not the most specific match for the destination 10.10.20.55, which falls under the more specific 10.10.20.0/24 route.
★ When this WOULD be the correct answer
In a different scenario where the 10.10.20.0/24 route is removed from the routing table, the 10.10.0.0/16 route would then be the only available route for the destination 10.10.20.55, making it the correct answer.
Why candidates choose this
Candidates may be tempted to choose this option because they recognize that the broader subnet covers the destination, leading them to mistakenly believe it is the best match.
Why this is wrong here
The default route is used only when no more specific routes match the destination address. Since 10.10.20.55 falls within the 10.10.20.0/24 subnet, the default route is not applicable in this case.
★ When this WOULD be the correct answer
If the question stated that the router only had a default route configured and no other specific routes for the 10.10.20.0/24 subnet, then the default route would be the only option available for reaching 10.10.20.55.
Why candidates choose this
Candidates may choose the default route due to a misunderstanding of routing priority, thinking that the default route serves as a catch-all for any unlisted addresses, without considering the specificity of the existing routes.
Why this is wrong here
This option is wrong because routers do not load-balance across routes unless configured to do so with specific routing protocols or settings. In this case, the most specific route, 10.10.20.0/24, is the only applicable choice for the destination 10.10.20.55.
★ When this WOULD be the correct answer
In a scenario where the router is configured with multiple equal-cost paths to the same destination, such as 10.10.20.0/24 and another route with the same prefix length, a question could ask which routes would be used for load balancing. In that case, the answer would be that the router load-balances across all matching routes.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of routing behavior, believing that routers automatically distribute traffic across all available routes rather than selecting the most specific match.
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
Remember that routers use the longest prefix match rule, not the most general or default route, when multiple routes are available.
Detailed technical explanation
In Cisco routing, the fundamental principle for route selection is the longest prefix match. This means the router examines all routes that match the destination IP address and selects the one with the most bits specified in the subnet mask. For example, a /24 prefix (255.255.255.0) specifies 24 bits of the address, making it more specific than a /16 prefix (255.255.0.0), which specifies only 16 bits. In the given scenario, the destination IP 10.10.20.55 matches both 10.10.0.0/16 and 10.10.20.0/24 routes. Since 10.10.20.0/24 covers a smaller, more specific subnet, the router chooses this route over the broader /16. The default route, which matches all addresses, is only used if no other route matches. Cisco routers do not load-balance across routes with different prefix lengths because that would violate the longest prefix match principle. Load balancing is possible only among routes with identical prefix lengths and administrative distances. This behavior ensures predictable and efficient routing. Practically, network engineers must design subnetting schemes carefully to avoid unintended route overlaps and ensure traffic flows through the intended paths. Understanding how prefix lengths affect route selection is essential for troubleshooting routing issues and optimizing network performance.
Key takeaway
Routers use the longest prefix match rule to select the most specific route for a given destination IP address.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review routers use the longest prefix match rule to select the most specific route for a given destination IP address., 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 — Routers use the longest prefix match rule to select the most specific route for a given destination IP address..
The correct answer is: The 10.10.20.0/24 route — The destination matches multiple routes, but the /24 is the most specific match and wins by longest prefix match.
Review routers use the longest prefix match rule to select the most specific route for a given destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
Routers use the longest prefix match rule to select the most specific route for a given destination IP address.
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Last reviewed: May 17, 2026
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