Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R1# show ip route O 172.16.10.0/24 [110/20] via 192.0.2.10 S 172.16.10.128/25 [1/0] via 192.0.2.6 Destination being tested: 172.16.10.130
Based on the exhibit, why is traffic to 172.16.10.130 using the static route instead of the OSPF route?
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
Best answer
Because the static /25 route is more specific than the OSPF /24 route.
This is correct because longest-prefix match selects the /25 for 172.16.10.130.
B
Distractor review
Because static routes always beat OSPF even when they are less specific.
This is wrong because specificity comes before source preference.
C
Distractor review
Because OSPF routes cannot be used for Class B networks.
This is wrong because OSPF can absolutely carry those routes.
D
Distractor review
Because the OSPF metric is lower than the static administrative distance.
This is wrong because the decisive factor here is prefix length, not that comparison.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is to incorrectly assume that static routes always override OSPF routes due to their lower administrative distance, regardless of prefix length. Candidates might also believe that OSPF cannot handle Class B networks or that metrics alone determine route selection. The trap lies in ignoring the fundamental routing principle of longest-prefix match, which Cisco routers apply before considering administrative distance or metric. This misunderstanding leads to incorrect answers and confusion about route selection behavior in Cisco routing tables.
Technical deep dive
How to think about this question
Routing decisions in Cisco networks rely heavily on the concept of longest-prefix match, where the router selects the route with the most specific subnet mask that matches the destination IP address. In this scenario, two routes exist for the destination 172.16.10.130: a static route with a /25 subnet mask and an OSPF-learned route with a /24 subnet mask. Since /25 (255.255.255.128) is more specific than /24 (255.255.255.0), the static route covers a smaller range of IP addresses and thus is preferred for routing traffic to that IP. When multiple routes to the same destination exist, Cisco routers first evaluate the prefix length to determine the most specific match. Only after prefix length does the router consider administrative distance or metric values. In this case, although OSPF routes typically have a lower administrative distance (110) compared to static routes (usually 1 if configured with no distance override), the static route’s longer prefix length takes precedence. This longest-prefix match rule ensures precise routing and optimal path selection. A common exam trap is to assume that administrative distance or routing protocol preference always determines route selection. However, Cisco routers prioritize prefix specificity before administrative distance. This means a less preferred routing protocol’s route can be chosen if it has a more specific subnet mask. Practically, this behavior allows network engineers to override dynamic routing with static routes for specific subnets by using more specific masks, providing granular control over traffic flow.
KKey Concepts to Remember
- Cisco routers select the route with the longest prefix match as the primary routing path for a given destination IP address.
- A static route with a more specific subnet mask (/25) is preferred over a dynamic OSPF route with a less specific subnet mask (/24) regardless of administrative distance.
- Administrative distance is considered only after the router identifies routes with the same prefix length to the destination network.
- OSPF routes have a default administrative distance of 110, while static routes typically have an administrative distance of 1 unless manually changed.
- Longest-prefix match ensures that traffic is routed through the most precise path available, improving routing accuracy and efficiency.
- Static routes can be used to override dynamic routing protocols for specific subnets by configuring more specific subnet masks.
- Cisco routing decisions do not prioritize routing protocol preference over prefix specificity, preventing less specific routes from overriding more specific ones.
- Understanding prefix length and longest-prefix match is critical for troubleshooting routing issues and designing effective routing policies 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.
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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?
Cisco routers select the route with the longest prefix match as the primary routing path for a given destination IP address.
What is the correct answer to this question?
The correct answer is: Because the static /25 route is more specific than the OSPF /24 route. — The static route is used because it is the more specific match. In practical terms, route selection starts with prefix specificity. The destination 172.16.10.130 matches both routes shown, but the static /25 is more specific than the OSPF /24. Because longest-prefix match comes first, the static route is chosen regardless of the different route sources. This is a classic route-selection interpretation question that tests whether you prioritize specificity correctly.
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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