Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A router learns 10.0.0.0/8 from OSPF and 10.10.0.0/16 from a static route. Which route is used for traffic to 10.10.20.1?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
The OSPF 10.0.0.0/8 route
This is wrong because the /8 is less specific than the matching /16.
B
Best answer
The static 10.10.0.0/16 route
This is correct because it is the more specific matching route.
C
Distractor review
The default route if present
This is wrong because more specific matching routes already exist.
D
Distractor review
Neither route, because the networks overlap
This is wrong because overlapping prefixes are normal and longest-prefix match resolves the decision.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent mistake is to assume that the OSPF route will be used simply because it is dynamically learned, or because it covers a larger network range. Candidates often overlook that the router applies longest-prefix match first, which means the more specific static route with a /16 mask takes precedence over the broader /8 OSPF route. This misunderstanding leads to incorrect answers, as the router does not ignore static routes in favor of OSPF when the static route is more specific. Remember, overlapping routes are common, and the router always chooses the route with the most specific subnet mask matching the destination.
Technical deep dive
How to think about this question
Routing decisions in Cisco devices rely heavily on the concept of longest-prefix match, which means the router selects the route with the most specific subnet mask that matches the destination IP address. In this scenario, the router has two routes: one learned via OSPF for 10.0.0.0/8 and one static route for 10.10.0.0/16. Both routes cover the destination IP 10.10.20.1, but the /16 prefix is more specific than the /8 prefix, narrowing the address range more precisely. When multiple routes to the same destination exist, Cisco routers first apply longest-prefix match to determine which route to use. After prefix length, the router considers administrative distance and metric to break ties if prefixes are equal. Here, the static route has an administrative distance of 1, which is lower than OSPF’s default 110, but since the static route is already more specific, it is selected regardless. This behavior ensures traffic is forwarded via the most precise and reliable path. A common exam trap is to assume that dynamic routing protocols like OSPF always take precedence over static routes. However, the router prioritizes prefix specificity first, then administrative distance. Overlapping routes are normal in routing tables, and the router uses longest-prefix match to resolve conflicts. Practically, this means that even if a broad OSPF route exists, more specific static routes will override it for matching destinations, ensuring optimal routing granularity.
KKey Concepts to Remember
- A Cisco router selects the route with the longest-prefix match as the primary forwarding path for a given destination IP address.
- Static routes have an administrative distance of 1, which is lower than OSPF’s default administrative distance of 110, making static routes more preferred when prefix lengths are equal.
- When multiple routes overlap, the router uses the most specific subnet mask to determine which route to install in the routing table.
- OSPF advertises routes dynamically but does not override more specific static routes in the routing table.
- The router performs route selection by first comparing prefix length, then administrative distance, and finally metric if needed.
- Overlapping routes in routing tables are normal and resolved by longest-prefix match, ensuring precise traffic forwarding.
- A broader route like 10.0.0.0/8 covers many addresses but is less specific than a 10.10.0.0/16 route for destinations within that range.
- Static routes provide explicit control over routing decisions and can override dynamic routes when configured with more specific prefixes.
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
A Cisco router selects the route with the longest-prefix match as the primary forwarding path for a given destination IP address.
What is the correct answer to this question?
The correct answer is: The static 10.10.0.0/16 route — The static /16 route is used because it is more specific than the OSPF /8 route. In practical terms, even though both routes match the destination, the router chooses the one that narrows the destination range more precisely. Since 10.10.20.1 belongs to 10.10.0.0/16, that entry wins. This question reinforces that longest-prefix match comes first. The broader OSPF route still matters for other destinations inside 10.0.0.0/8, but not for this one.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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