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: administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths.. 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 the same destination prefix from OSPF and EIGRP. The prefix length is identical, and both routes are valid. Which route is preferred by default?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The EIGRP route
The EIGRP route is preferred by default because EIGRP has a lower default administrative distance than OSPF. In practical terms, once the prefix length is the same, the router compares source trust. Lower administrative distance wins. EIGRP’s default of 90 beats OSPF’s default of 110.
This is not a longest-prefix question. The prefix is identical, so the decision is about source preference rather than specificity.
Key principle: Administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
Administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths.
In a different scenario where OSPF is configured with a lower administrative distance than EIGRP, or if EIGRP is configured with a higher AD, the OSPF route would be preferred. For example, a question might specify that OSPF is set to an AD of 90 and EIGRP to 170, making the OSPF route the correct choice.
✗
Both routes are installed equally because the prefix length matches
Why it's wrong here
This is wrong because equal prefix length alone does not make the routes equally preferred.
When this WOULD be correct
In a different scenario where both OSPF and EIGRP are configured to use equal-cost multi-path (ECMP) routing, the question could state that both protocols are allowed to install routes with the same prefix length, making this option correct as both routes would be used equally.
✗
Neither route is used because protocols cannot advertise the same prefix
Why it's wrong here
This is wrong because routers can receive the same prefix from multiple sources and choose one.
When this WOULD be correct
If the exam question stated that the router was configured to only accept routes from one protocol due to specific policy or filtering rules, then the option stating that neither route is used could be correct, as only the preferred protocol would be allowed to install routes.
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 EIGRP routeCorrect answer▾
Why this is correct
This is correct because EIGRP's default administrative distance is lower than OSPF's.
✗The OSPF routeWrong answer — click to see why▾
Why this is wrong here
OSPF has a default administrative distance of 110, which is higher than EIGRP's 90. Since a lower AD is preferred, the OSPF route is not chosen over EIGRP for the same prefix.
★ When this WOULD be the correct answer
In a different scenario where OSPF is configured with a lower administrative distance than EIGRP, or if EIGRP is configured with a higher AD, the OSPF route would be preferred. For example, a question might specify that OSPF is set to an AD of 90 and EIGRP to 170, making the OSPF route the correct choice.
Why candidates choose this
Students may confuse OSPF's fast convergence or link-state nature with a higher preference, or they might think OSPF is always preferred because it is an open standard protocol.
✗Both routes are installed equally because the prefix length matchesWrong answer — click to see why▾
Why this is wrong here
Equal prefix length does not determine route preference; the router uses administrative distance to break ties between routes from different protocols. Both routes can be installed if they have different ADs, but only the one with lower AD is used.
★ When this WOULD be the correct answer
In a different scenario where both OSPF and EIGRP are configured to use equal-cost multi-path (ECMP) routing, the question could state that both protocols are allowed to install routes with the same prefix length, making this option correct as both routes would be used equally.
Why candidates choose this
Students often think that matching prefix lengths means equal preference, but they overlook the role of administrative distance in multi-protocol routing.
✗Neither route is used because protocols cannot advertise the same prefixWrong answer — click to see why▾
Why this is wrong here
Routers can learn the same prefix from multiple routing protocols; this is common in networks running multiple protocols. The router selects the best route based on administrative distance, not discarding routes.
★ When this WOULD be the correct answer
If the exam question stated that the router was configured to only accept routes from one protocol due to specific policy or filtering rules, then the option stating that neither route is used could be correct, as only the preferred protocol would be allowed to install routes.
Why candidates choose this
A beginner might think that duplicate routes cause conflicts or loops, but routing protocols are designed to handle multiple sources and choose the best path.
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 believing that when two routing protocols advertise the same prefix with identical prefix lengths, the router installs both routes equally or performs load balancing. This misconception ignores the role of administrative distance, which is the primary factor in route preference when prefix lengths match. Another trap is thinking that OSPF is always preferred because it is a widely used IGP, but Cisco routers prioritize routes based on AD values, not protocol popularity. Misunderstanding this can lead to incorrect answers about route selection in multi-protocol environments.
Detailed technical explanation
How to think about this question
Administrative distance (AD) is a Cisco-specific value that routers use to select the best path when multiple routing protocols provide routes to the same destination prefix. Each routing protocol has a default AD value representing its trustworthiness; lower values indicate more preferred routes. EIGRP has a default AD of 90, while OSPF’s default AD is 110. When a router receives identical prefixes from both EIGRP and OSPF, it compares their ADs to decide which route to install in the routing table.
The decision process for route selection starts with the longest prefix match, but since the prefix lengths are identical in this scenario, the router moves to the next criterion: administrative distance. The route with the lower AD is preferred and installed in the routing table. Therefore, the EIGRP route with AD 90 is chosen over the OSPF route with AD 110. Metrics within each protocol are only considered if the ADs are equal, which is not the case here.
A common exam trap is assuming that equal prefix length means both routes are installed or that routing protocols cannot advertise the same prefix simultaneously. In reality, routers can learn the same prefix from multiple protocols but always prefer the route with the lowest AD. Practically, this ensures stable and predictable routing behavior, avoiding routing loops or conflicts by trusting the more reliable protocol according to Cisco’s AD hierarchy.
KKey Concepts to Remember
Administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths.
EIGRP has a default administrative distance of 90, which is lower and more preferred than OSPF’s default administrative distance of 110.
Routers compare administrative distance values to select the best route before considering metrics within each routing protocol.
Identical prefix lengths cause routers to rely on administrative distance rather than longest-prefix match for route selection.
Routers can learn the same prefix from multiple routing protocols but install only the route with the lowest administrative distance.
Equal prefix length alone does not cause routers to install multiple routes; administrative distance governs route preference.
OSPF routes are less preferred than EIGRP routes by default due to their higher administrative distance value.
Understanding administrative distance helps avoid common exam mistakes related to multi-protocol route selection.
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
Administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths.
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 administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — Administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths..
What is the correct answer to this question?
The correct answer is: The EIGRP route — The EIGRP route is preferred by default because EIGRP has a lower default administrative distance than OSPF. In practical terms, once the prefix length is the same, the router compares source trust. Lower administrative distance wins. EIGRP’s default of 90 beats OSPF’s default of 110.
This is not a longest-prefix question. The prefix is identical, so the decision is about source preference rather than specificity.
What should I do if I get this 200-301 question wrong?
Review administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Administrative distance determines route preference when multiple routing protocols advertise the same destination prefix with identical prefix lengths.
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