CCNA IP Routing Practice Question
A router has routes to 192.168.100.0/24 and 192.168.100.128/25. Which route is used for traffic to 192.168.100.140?
⚠ Common exam trap
A frequent exam trap is assuming that the less specific route (192.168.100.0/24) will be used simply because it covers the entire subnet range or because it might have a better administrative distance. Candidates might also think overlapping prefixes cause routing conflicts that prevent either route from being used. However, Cisco routers resolve overlapping routes by always selecting the longest prefix match, which is the most specific subnet. Ignoring this rule leads to incorrect answers and misunderstanding of routing behavior.
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
✓
192.168.100.128/25
The /25 route is used because it is the most specific matching prefix. In practical terms, 192.168.100.140 falls inside the upper half of the /24, which is exactly what the 192.168.100.128/25 route describes. Even though the /24 also matches, the router always prefers the narrower route when both are valid. This is a direct longest-prefix-match question. It reinforces that specificity is checked before broader route-source preferences matter.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
192.168.100.0/24
Why it's wrong here
This is wrong because the /24 is less specific than the matching /25.
When this WOULD be correct
In a scenario where the question asks which route would be used for traffic to an IP address like 192.168.100.50, the option 192.168.100.0/24 would be correct, as it encompasses the entire /24 subnet and is the only applicable route for that address.
- ✓
192.168.100.128/25
Why this is correct
This is correct because .140 falls within the 192.168.100.128/25 range.
- ✗
The default route
Why it's wrong here
This is wrong because a more specific route already matches.
When this WOULD be correct
In a different question context where no specific routes are defined for the destination IP, and the router has only a default route configured (0.0.0.0/0), the default route would be the only option available for routing traffic to any unknown destination.
- ✗
Neither route, because the prefixes overlap
Why it's wrong here
This is wrong because overlapping prefixes are normal and longest-prefix match resolves the choice.
When this WOULD be correct
In a scenario where the question states that both routes are configured with the same prefix length and the router is set to prefer the longest prefix match, a question could ask which route is used for a specific address, leading to confusion about overlapping routes. In that case, if both routes were truly overlapping, the answer could be 'neither' due to ambiguity.
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.
✓192.168.100.128/25Correct answer▾
Why this is correct
This is correct because .140 falls within the 192.168.100.128/25 range.
✗192.168.100.0/24Wrong answer — click to see why▾
Why this is wrong here
The route 192.168.100.0/24 covers the entire /24 subnet, but it is less specific than the /25 route for the destination 192.168.100.140. The router uses the longest prefix match, so the /25 route is preferred.
★ When this WOULD be the correct answer
In a scenario where the question asks which route would be used for traffic to an IP address like 192.168.100.50, the option 192.168.100.0/24 would be correct, as it encompasses the entire /24 subnet and is the only applicable route for that address.
Why candidates choose this
Students might think that because 192.168.100.140 falls within the /24 range, the /24 route would be used, forgetting that a more specific (longer prefix) route takes precedence.
✗The default routeWrong answer — click to see why▾
Why this is wrong here
A default route (0.0.0.0/0) is only used when no more specific route matches the destination. Since there is a matching /25 route, the default route is not considered.
★ When this WOULD be the correct answer
In a different question context where no specific routes are defined for the destination IP, and the router has only a default route configured (0.0.0.0/0), the default route would be the only option available for routing traffic to any unknown destination.
Why candidates choose this
Students may confuse the concept of default route with a catch-all, thinking it might be used when there are overlapping routes, but the longest prefix match rule always applies first.
✗Neither route, because the prefixes overlapWrong answer — click to see why▾
Why this is wrong here
Overlapping prefixes are common in routing tables and do not prevent route selection. The router uses the longest prefix match to choose the best route, so both routes can coexist without conflict.
★ When this WOULD be the correct answer
In a scenario where the question states that both routes are configured with the same prefix length and the router is set to prefer the longest prefix match, a question could ask which route is used for a specific address, leading to confusion about overlapping routes. In that case, if both routes were truly overlapping, the answer could be 'neither' due to ambiguity.
Why candidates choose this
Some students might think overlapping routes cause ambiguity or errors, but routers are designed to handle them by selecting the most specific prefix.
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.
Go deeper
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
Key term
Route
A route is a path that data takes through a network from one device or network to another, determined by routing protocols and configured rules.
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.
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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.