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: a Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a 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 learns 172.16.0.0/16 from OSPF and 172.16.10.0/24 from a static route. Which route is used for traffic to 172.16.10.55?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The static /24 route
The static /24 route is used because it is more specific than the OSPF /16 route. In plain language, even though OSPF is a dynamic source and the /16 covers the destination broadly, the router prefers the entry that describes the exact destination range more precisely. Since 172.16.10.55 falls within 172.16.10.0/24, that route wins under longest-prefix match.
This is a classic example of route specificity taking priority before broader route-source comparisons would matter between equal prefix lengths.
Key principle: A Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address.
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 OSPF /16 route
Why it's wrong here
This is wrong because the /16 is less specific than the matching /24 route.
When this WOULD be correct
In a different scenario where the static route is removed or not configured, the OSPF /16 route would be the only available route for traffic to 172.16.10.55. Thus, the OSPF route would be the correct answer in that case.
✓
The static /24 route
Why this is correct
This is correct because 172.16.10.55 falls within the more specific /24 route.
Related concept
A Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address.
✗
The default route
Why it's wrong here
This is wrong because a specific matching route exists and is preferred.
When this WOULD be correct
In a different question where the router has no specific routes for the destination IP address and only a default route configured, traffic to an unknown destination would use the default route. For example, if the question stated that the router only had a default route and no other specific routes for 172.16.10.55, then the default route would be correct.
✗
Neither route because the prefixes overlap
Why it's wrong here
This is wrong because overlapping routes are normal and longest-prefix match resolves the choice.
When this WOULD be correct
In a scenario where a question states that both routes are configured but the static route is incorrectly defined as 172.16.0.0/24 instead of /16, the option D would be correct, as both routes would overlap and cause ambiguity in routing decisions.
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 static /24 routeCorrect answer▾
Why this is correct
This is correct because 172.16.10.55 falls within the more specific /24 route.
✗The OSPF /16 routeWrong answer — click to see why▾
Why this is wrong here
The OSPF /16 route is less specific than the static /24 route. For traffic to 172.16.10.55, the /24 route provides a longer prefix match (24 bits vs 16 bits), so it is preferred regardless of administrative distance or routing protocol.
★ When this WOULD be the correct answer
In a different scenario where the static route is removed or not configured, the OSPF /16 route would be the only available route for traffic to 172.16.10.55. Thus, the OSPF route would be the correct answer in that case.
Why candidates choose this
Students may think OSPF is preferred over static routes due to lower administrative distance, but they forget that longest-prefix match is evaluated first. The /16 route covers the destination but is not the most specific match.
✗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 a matching /24 route exists for 172.16.10.55, the default route is not considered.
★ When this WOULD be the correct answer
In a different question where the router has no specific routes for the destination IP address and only a default route configured, traffic to an unknown destination would use the default route. For example, if the question stated that the router only had a default route and no other specific routes for 172.16.10.55, then the default route would be correct.
Why candidates choose this
Students might think that if a route is learned via OSPF and a static route exists, the router might fall back to a default route. However, the presence of any matching route (even a static one) prevents the default route from being used.
✗Neither route because the prefixes overlapWrong answer — click to see why▾
Why this is wrong here
Overlapping routes are common in routing tables and are resolved by the longest-prefix match algorithm. The router selects the most specific route (the /24) for the destination, so there is no conflict or ambiguity.
★ When this WOULD be the correct answer
In a scenario where a question states that both routes are configured but the static route is incorrectly defined as 172.16.0.0/24 instead of /16, the option D would be correct, as both routes would overlap and cause ambiguity in routing decisions.
Why candidates choose this
Some students may incorrectly believe that overlapping prefixes cause a routing loop or error, but routers handle overlapping routes by choosing the most specific match. This is a fundamental concept in IP routing.
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
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that the dynamic OSPF route will always be preferred over a static route, regardless of prefix length. Many candidates overlook that the router prioritizes the longest-prefix match before considering administrative distance or route source. Because 172.16.10.0/24 is more specific than 172.16.0.0/16, the router uses the static route for traffic to 172.16.10.55. Misunderstanding this can lead to incorrect answers, especially when both routes overlap. Remember, overlapping routes are common and resolved by prefix specificity, not by route type alone.
Detailed technical explanation
How to think about this question
Routing decisions in Cisco routers rely heavily on the concept of longest-prefix match, where the most specific route to a destination IP address is preferred over less specific ones. In this scenario, the router has learned two routes for the 172.16.0.0 network: a /16 prefix from OSPF and a more specific /24 prefix from a static route. The /24 subnet mask covers a smaller, more precise range of IP addresses, including 172.16.10.55, making it the preferred route for traffic destined to that IP.
The router first matches the destination IP against all known routes and selects the route with the longest subnet mask (most bits matched). Even though OSPF is a dynamic routing protocol and static routes typically have a lower administrative distance, the key factor here is prefix length. The static /24 route is more specific than the OSPF /16 route, so the router uses the static route for forwarding packets to 172.16.10.55. Administrative distance would only come into play if two routes had the same prefix length.
A common exam trap is confusing route preference with administrative distance or the routing protocol source. Candidates might incorrectly assume OSPF routes always override static routes or that overlapping prefixes cause routing conflicts. In reality, overlapping prefixes are normal, and the router always uses the longest-prefix match rule first. This behavior ensures precise routing and efficient traffic forwarding in complex networks, reflecting real-world Cisco routing operations.
KKey Concepts to Remember
A Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address.
Static routes with a more specific subnet mask are preferred over less specific dynamic routes when both cover the destination IP.
OSPF advertises routes dynamically but does not override a static route if the static route has a longer prefix length.
Administrative distance is only compared when two routes have the same prefix length to the same destination network.
Overlapping IP prefixes are common in routing tables and are resolved by choosing the route with the longest subnet mask.
The router forwards packets based on the route entry that precisely matches the destination IP address range.
Static routes are manually configured and can provide more specific routing entries than dynamically learned routes.
Understanding prefix length and longest-prefix match is critical for accurate routing decisions in Cisco networks.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
A Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review a Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — A Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address..
What is the correct answer to this question?
The correct answer is: The static /24 route — The static /24 route is used because it is more specific than the OSPF /16 route. In plain language, even though OSPF is a dynamic source and the /16 covers the destination broadly, the router prefers the entry that describes the exact destination range more precisely. Since 172.16.10.55 falls within 172.16.10.0/24, that route wins under longest-prefix match.
This is a classic example of route specificity taking priority before broader route-source comparisons would matter between equal prefix lengths.
What should I do if I get this 200-301 question wrong?
Review a Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
A Cisco router uses the longest-prefix match rule to select the most specific route to forward traffic to a destination IP address.
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