CCNA IP Routing Practice Question
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?
⚠ Common exam trap
Remember that routers use the longest prefix match rule, not the most general or default route, when multiple routes are available.
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
✓
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.
Answer analysis
Option-by-option breakdown
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 10.10.0.0/16 route does match the destination 10.10.20.55, but it is less specific than the /24 route. The router always prefers the longest prefix match, so a /16 will never be chosen when a /24 for the same destination network exists. If the /24 route were removed, then the /16 would be the best match and would be used, but not in this scenario.
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 not used because the router applies the longest prefix match algorithm, and the route for 10.10.20.0/24 (a /24) is a more specific match for destination 10.10.20.55 than the default route (a /0). This option is tempting because a default route serves as a catch-all for any destination not found in the routing table; it would be the correct choice only if no other route in the table matched the destination address.
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
The 10.10.20.0/24 route is selected because the router's forwarding decision uses the longest prefix match algorithm. For a destination of 10.10.20.55, this /24 route is the most specific match, covering the exact subnet that contains the address. Even though the default route and the /16 route also match, they have shorter prefixes and are therefore less specific, making the /24 the only candidate used.
- ✗
The router load-balances across all matching routes
Why it's wrong here
The router does not load-balance across routes with different prefix lengths. ECMP (Equal-Cost Multipath) applies only to multiple routes with the same prefix length and the same administrative distance/metric. Here, the /24, /16, and default route are different subnet masks, so they represent different levels of specificity; the forwarding engine selects exactly one route—the longest match—and does not distribute traffic among them.
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
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.
✓The 10.10.20.0/24 routeCorrect answer▾
Why this is correct
The 10.10.20.0/24 route is selected because the router's forwarding decision uses the longest prefix match algorithm. For a destination of 10.10.20.55, this /24 route is the most specific match, covering the exact subnet that contains the address. Even though the default route and the /16 route also match, they have shorter prefixes and are therefore less specific, making the /24 the only candidate used.
✗The 10.10.0.0/16 routeWrong answer — click to see why▾
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.
✗The default routeWrong answer — click to see why▾
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.
✗The router load-balances across all matching routesWrong answer — click to see why▾
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?”
Visual reference
Quick reference
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
Go deeper
Related to this question
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Interpreting HSRP and VRRP Operational Status
Key term
Router
A router is a networking device that connects different networks together and directs data traffic between them by choosing the best path for data to travel.
Key term
Default route
A default route is a catch-all routing entry that tells a network device where to send packets when no specific route matches the destination address.
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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.