Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
What is the main reason a more specific route usually overrides a less specific route, even when both point to valid destinations?
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 routing prefers the most specific matching prefix.
This is correct because longest-prefix match is the rule that gives more specific routes priority.
B
Distractor review
Because less specific routes are always invalid.
This is wrong because summary and default routes are valid and useful; they are just less specific.
C
Distractor review
Because more specific routes always have a lower administrative distance.
This is wrong because specificity and administrative distance are separate concepts.
D
Distractor review
Because OSPF requires every route to be /32.
This is wrong because OSPF supports many prefix lengths and does not require /32 routes.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that the route with the lowest administrative distance or a specific routing protocol preference always overrides others, regardless of prefix length. Candidates might incorrectly think that OSPF requires /32 routes or that less specific routes are invalid. This misunderstanding leads to choosing answers based on protocol rules or administrative distance alone, ignoring the fundamental longest-prefix match principle. Remember, the router always prefers the most specific route that matches the destination IP, even if the less specific route has a better administrative distance or comes from a preferred protocol.
Technical deep dive
How to think about this question
Routing in IP networks relies on the principle of longest-prefix match, which means that when a router receives a packet, it searches its routing table for the route entry with the most specific subnet mask that matches the destination IP address. This specificity is determined by the prefix length: the longer the prefix, the more specific the route. For example, a /28 route is more specific than a /24 route. This ensures that traffic is forwarded along the most precise path available, optimizing network efficiency and accuracy. The decision process in routing involves comparing all matching routes for a destination and selecting the one with the longest prefix. This rule overrides other factors like administrative distance or metric when multiple routes point to the same destination but differ in specificity. Cisco routers implement this longest-prefix match rule consistently, which means that even if a less specific route has a better administrative distance, the more specific route will be preferred if both are valid. A common exam trap is confusing route specificity with administrative distance or protocol requirements. For example, some may incorrectly believe that OSPF requires /32 routes or that more specific routes always have lower administrative distances. In reality, OSPF supports various prefix lengths, and administrative distance is a separate metric used only when prefix lengths are equal. Understanding this distinction helps avoid mistakes and clarifies why routing tables prioritize longest-prefix matches for precise packet forwarding.
KKey Concepts to Remember
- A router uses the longest-prefix match rule to select the most specific route that matches the destination IP address for packet forwarding.
- Routing decisions prioritize prefix length specificity over administrative distance when multiple valid routes to the same destination exist.
- Administrative distance is used only when routes have equal prefix lengths to determine the preferred routing protocol.
- Routing protocols like OSPF and EIGRP support a variety of prefix lengths and do not require fixed subnet masks such as /32.
- Less specific routes, such as default or summary routes, remain valid and are used only when no more specific route matches the destination.
- The longest-prefix match ensures precise and predictable routing behavior, especially when detailed and summary routes coexist in the routing table.
- Routers compare all matching routes and install the route with the longest prefix in the forwarding table for efficient packet delivery.
- Confusing route specificity with administrative distance or protocol requirements can lead to incorrect routing decisions and exam mistakes.
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 router uses the longest-prefix match rule to select the most specific route that matches the destination IP address for packet forwarding.
What is the correct answer to this question?
The correct answer is: Because routing prefers the most specific matching prefix. — A more specific route overrides a less specific route because longest-prefix match is the core logic used for route selection among matching destinations. In plain language, the router prefers the entry that most narrowly and accurately describes the actual destination network. This makes routing behavior precise and predictable, especially when summary routes and more detailed routes coexist. If routers did not prefer the more specific match, detailed route information would not provide much value. The correct answer is the one that explains route choice in terms of specificity rather than protocol type alone.
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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