CCNA IP Routing Practice Question
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?
⚠ Common exam trap
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.
Answer choices
Why each option matters
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.
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 EIGRP route
Why this is correct
The EIGRP route is preferred because EIGRP's default administrative distance (AD) of 90 is lower than OSPF's default AD of 110. When a router receives the same destination prefix from multiple routing protocols, it compares AD values and installs the route with the lowest AD into the routing table. Therefore, the EIGRP route wins this selection.
- ✗
The OSPF route
Why it's wrong here
The OSPF route is not installed because its default administrative distance of 110 is higher than EIGRP's default AD of 90. Administrative distance acts as a preference rating for routing protocol sources, and OSPF's higher value makes it less trustworthy than EIGRP for the same prefix. Even though OSPF is a valid routing protocol, the lower-AD EIGRP route takes precedence.
When this WOULD be correct
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
Equal prefix length alone does not make routes equally preferred; longest-prefix matching only applies when comparing routes with different subnet masks. Since both OSPF and EIGRP advertise the same prefix and mask, the router must use administrative distance as the next tiebreaker. The route with the lower AD—EIGRP's 90 versus OSPF's 110—is selected exclusively.
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
A router absolutely can receive the same destination prefix from multiple routing protocols; this is a common scenario in networks running both OSPF and EIGRP. Routing protocols do not prohibit overlapping route advertisements, and the router simply selects the best one using administrative distance. Thus, neither route is ignored; the EIGRP route is chosen and placed in the routing table.
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
The EIGRP route is preferred because EIGRP's default administrative distance (AD) of 90 is lower than OSPF's default AD of 110. When a router receives the same destination prefix from multiple routing protocols, it compares AD values and installs the route with the lowest AD into the routing table. Therefore, the EIGRP route wins this selection.
✗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?”
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
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Key term
Route
A route is a path that data takes through a network from one device or network to another, determined by routing protocols and configured rules.
Key term
EIGRP
EIGRP is an advanced distance-vector routing protocol that uses bandwidth and delay by default to find the best path for data packets across a computer network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.