The static /24 route is the correct choice because the longest prefix match rule dictates that the most specific route always wins, regardless of administrative distance or routing protocol. When forwarding traffic to 10.55.10.25, the router compares the destination against all routes in the routing table and selects the one with the longest matching subnet mask; the /24 mask matches 24 bits, while the OSPF /16 matches only 16 bits, making the static route more precise. On the CCNA 200-301 v2 exam, this concept frequently appears in questions that try to trick you into comparing administrative distance values—a common trap where students mistakenly think OSPF’s lower AD would override the static route. Remember, AD only breaks ties between routes with the same prefix length; longest prefix match is always evaluated first. A helpful memory tip: think of it like a zip code—a more specific code (like a 5+4 digit code) gets your mail delivered before a general one, no matter how trustworthy the general address seems.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: cisco routers use the longest-prefix match rule to select the most specific route that matches the 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.
R1 receives an OSPF route to 10.55.0.0/16 and already has a static route to 10.55.10.0/24. Which route will be used for traffic sent to 10.55.10.25?
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, because it is the longest-prefix match.
The static /24 route is more specific than the OSPF /16 route, so longest-prefix match wins. Administrative distance is only compared among routes to the same prefix length.
Key principle: Cisco routers use the longest-prefix match rule to select the most specific route that matches the 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, because dynamic routes override static routes learned later.
Why it's wrong here
Dynamic routes do not override a more specific route just because they are dynamic.
When this WOULD be correct
In a scenario where the question states that OSPF routes are configured with a higher administrative distance than static routes, the OSPF /16 route could override the static route. For example, if the static route had an administrative distance of 200 and the OSPF route had an administrative distance of 110, the OSPF route would be used.
✓
The static /24 route, because it is the longest-prefix match.
Why this is correct
Route lookup prefers the most specific matching prefix.
Related concept
Cisco routers use the longest-prefix match rule to select the most specific route that matches the destination IP address.
✗
Both routes equally, because they point to the same major network.
Why it's wrong here
Major network boundaries do not create equal-cost behavior.
When this WOULD be correct
In a different scenario where both routes are configured with equal administrative distances and no specific prefix matching rules apply, a question might ask which route would be used if both were equally preferred. In such a case, the answer could be that both routes are considered equally valid for traffic to the same major network.
✗
Neither route, because overlapping routes are invalid.
Why it's wrong here
Overlapping routes are normal in IP routing.
When this WOULD be correct
In a different scenario, if the question stated that the routing table had a configuration that explicitly marked overlapping routes as invalid or if the router was configured to reject any overlapping static routes, then this option could be correct.
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 route, because it is the longest-prefix match.Correct answer▾
Why this is correct
Route lookup prefers the most specific matching prefix.
✗The OSPF /16 route, because dynamic routes override static routes learned later.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because static routes are preferred over dynamic routes in OSPF when both are present, regardless of when they were learned. The static route to 10.55.10.0/24 will be used due to its longer prefix match.
★ When this WOULD be the correct answer
In a scenario where the question states that OSPF routes are configured with a higher administrative distance than static routes, the OSPF /16 route could override the static route. For example, if the static route had an administrative distance of 200 and the OSPF route had an administrative distance of 110, the OSPF route would be used.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of OSPF's behavior, believing that dynamic routes always take precedence over static routes, especially if they are not familiar with the concept of administrative distance.
✗Both routes equally, because they point to the same major network.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPF routes do not share equal preference with static routes; the static /24 route will be preferred due to its longer prefix length, making it the best match for the specific destination IP.
★ When this WOULD be the correct answer
In a different scenario where both routes are configured with equal administrative distances and no specific prefix matching rules apply, a question might ask which route would be used if both were equally preferred. In such a case, the answer could be that both routes are considered equally valid for traffic to the same major network.
Why candidates choose this
Candidates may find this option tempting because it suggests that multiple routes can be utilized simultaneously, reflecting a common networking concept where multiple paths exist for the same destination.
✗Neither route, because overlapping routes are invalid.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because overlapping routes are valid in routing protocols like OSPF, and both routes can coexist in the routing table. The static route to 10.55.10.0/24 is valid and will be preferred due to its longer prefix length.
★ When this WOULD be the correct answer
In a different scenario, if the question stated that the routing table had a configuration that explicitly marked overlapping routes as invalid or if the router was configured to reject any overlapping static routes, then this option could be correct.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of how routing protocols handle overlapping routes, mistakenly believing that any overlap renders routes invalid rather than recognizing the preference rules that apply.
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
Remember that the longest-prefix match rule takes precedence over administrative distance when routes have different prefix lengths.
Detailed technical explanation
How to think about this question
Routing decisions in Cisco devices rely primarily on the longest-prefix match rule, which means the router selects the route with the most specific subnet mask that matches the destination IP address. In this scenario, R1 has two routes: an OSPF-learned route to 10.55.0.0/16 and a static route to 10.55.10.0/24. Since 10.55.10.25 falls within both prefixes, the router compares the subnet masks and prefers the /24 static route because it is more specific than the /16 OSPF route.
Administrative distance (AD) is a secondary factor used only when two routes have the exact same prefix length. AD ranks route sources by trustworthiness, with static routes typically having a lower AD (higher trust) than OSPF routes. However, because the static route here is more specific, the router does not need to compare AD values. The longest-prefix match rule always takes precedence over AD when prefixes differ in length.
A common exam trap is to assume dynamic routing protocols like OSPF always override static routes because they are learned dynamically. This is incorrect because Cisco routers prioritize the most specific route first. In practical networking, overlapping routes are normal and essential for route summarization and policy routing. Understanding this behavior helps avoid misconfigurations and ensures predictable routing outcomes.
KKey Concepts to Remember
Cisco routers use the longest-prefix match rule to select the most specific route that matches the destination IP address.
Static routes have a default administrative distance of 1, which is lower than OSPF's default of 110, making static routes more trusted when prefix lengths are equal.
When multiple routes to the same destination exist, the router first compares prefix lengths before considering administrative distance.
OSPF advertises routes dynamically with a default administrative distance of 110, but it does not override more specific static routes.
Overlapping routes with different subnet masks are valid and common in IP routing to allow granular traffic forwarding.
Route lookup in Cisco IOS always prefers the route with the longest subnet mask, regardless of whether the route is static or dynamic.
Administrative distance is only compared when two routes have the same prefix length and destination network.
Static routes provide precise control over routing decisions and can override dynamic routes if they are more specific.
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
Cisco routers use the longest-prefix match rule to select the most specific route that matches the 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 cisco routers use the longest-prefix match rule to select the most specific route that matches the destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — Cisco routers use the longest-prefix match rule to select the most specific route that matches the destination IP address..
What is the correct answer to this question?
The correct answer is: The static /24 route, because it is the longest-prefix match. — The static /24 route is more specific than the OSPF /16 route, so longest-prefix match wins. Administrative distance is only compared among routes to the same prefix length.
What should I do if I get this 200-301 question wrong?
Review cisco routers use the longest-prefix match rule to select the most specific route that matches the 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?
Cisco routers use the longest-prefix match rule to select the most specific route that matches the destination IP address.
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