The answer is EIGRP, because when a router receives two routes to the same destination with identical prefix lengths, it selects the route with the lowest administrative distance. EIGRP’s default administrative distance of 90 is lower than OSPF’s 110, making the EIGRP-sourced route more trustworthy and therefore preferred for installation in the routing table. This administrative distance comparison between EIGRP and OSPF is a classic CCNA 200-301 v2 exam trap: many students mistakenly apply the longest-prefix match rule here, but since the prefix lengths are equal, the decision hinges solely on source preference. The exam tests your ability to distinguish between prefix-length logic and administrative-distance logic in route selection. A helpful memory tip is to think of administrative distance as a “trust score” where lower is better—EIGRP at 90 is more reliable than OSPF at 110, so EIGRP wins every time the prefixes match.
CCNA IP Routing Practice Question
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 is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols.. 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 receives a destination prefix from EIGRP with administrative distance 90 and also from OSPF with administrative distance 110. The prefix length is identical. Which route source is preferred?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
EIGRP
The EIGRP route is preferred because its administrative distance is lower. In practical terms, once the prefix length is the same, the router compares the trustworthiness of the route source. Lower administrative distance wins. Since 90 is lower than 110, EIGRP is preferred over OSPF for that destination.
This is an administrative-distance comparison question, not a longest-prefix question. The key is that the prefix length is equal, so source preference becomes the deciding factor.
Key principle: Administrative distance is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
In a different question setup, if the administrative distance for OSPF were lower than that of EIGRP (e.g., OSPF 90 and EIGRP 110), then OSPF would be the preferred route source for the identical prefix length.
In a different question setup where both EIGRP and OSPF provide routes with the same administrative distance and prefix length, the candidate might be asked which routes would be preferred. In that case, the correct answer could be 'both equally' as they would be treated with the same preference.
✗
Neither, because route sources cannot overlap
Why it's wrong here
This is wrong because routers can compare and choose between multiple sources for the same prefix.
When this WOULD be correct
In a scenario where the question specifies that a router cannot use routes from multiple sources for the same destination prefix, such as in a strict routing policy or a specific network design requirement, this option would be correct.
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.
✓EIGRPCorrect answer▾
Why this is correct
This is correct because EIGRP’s default administrative distance of 90 is lower than OSPF’s 110.
✗OSPFWrong 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. Therefore, OSPF is not preferred when both protocols provide a route to the same destination prefix.
★ When this WOULD be the correct answer
In a different question setup, if the administrative distance for OSPF were lower than that of EIGRP (e.g., OSPF 90 and EIGRP 110), then OSPF would be the preferred route source for the identical prefix length.
Why candidates choose this
Students might think OSPF is more reliable or commonly used in larger networks, leading them to assume it would be preferred over EIGRP, but administrative distance is the decisive factor.
✗Both equallyWrong answer — click to see why▾
Why this is wrong here
When two routing protocols provide routes to the same prefix, the router selects the one with the lower administrative distance. Since EIGRP's AD (90) is lower than OSPF's (110), they are not equally preferred.
★ When this WOULD be the correct answer
In a different question setup where both EIGRP and OSPF provide routes with the same administrative distance and prefix length, the candidate might be asked which routes would be preferred. In that case, the correct answer could be 'both equally' as they would be treated with the same preference.
Why candidates choose this
A student might confuse administrative distance with metric, thinking that if both routes have the same metric they would be equal, but AD is compared first and differs here.
✗Neither, because route sources cannot overlapWrong answer — click to see why▾
Why this is wrong here
Routers can receive the same prefix from multiple routing protocols and will compare administrative distances to choose the best route. This is a common scenario in networks running multiple protocols, so route sources can overlap.
★ When this WOULD be the correct answer
In a scenario where the question specifies that a router cannot use routes from multiple sources for the same destination prefix, such as in a strict routing policy or a specific network design requirement, this option would be correct.
Why candidates choose this
A student might think that different routing protocols cannot both know about the same network, but in practice, route redistribution or multiple protocols on the same router can lead to overlapping prefixes.
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 to assume that OSPF routes might be preferred over EIGRP routes simply because OSPF is a widely used IGP or because of metric comparisons within OSPF. Candidates often confuse administrative distance with routing metrics, mistakenly thinking that the lower metric route is preferred regardless of protocol. However, administrative distance is the first criterion when routes come from different protocols. Another trap is to think that routes from different protocols cannot overlap or that prefix length alone determines preference. The key is that when prefix lengths are equal, the router uses administrative distance to select the best route, so EIGRP’s lower AD of 90 always beats OSPF’s 110.
Detailed technical explanation
How to think about this question
Administrative distance (AD) is a key Cisco routing concept that determines the trustworthiness of routing information received from different routing protocols. Each routing protocol has a default AD value, which is a numeric ranking used by routers to select the best path when multiple protocols provide routes to the same destination. Lower AD values indicate more trusted sources. For example, EIGRP has a default AD of 90, while OSPF has a default AD of 110, meaning EIGRP routes are preferred over OSPF routes if both advertise the same prefix.
When a router receives routes to the same destination prefix with identical prefix lengths from multiple routing protocols, it compares their administrative distances to decide which route to install in the routing table. The route with the lowest AD is selected because it is considered more reliable. In this scenario, since EIGRP’s AD (90) is lower than OSPF’s AD (110), the router prefers the EIGRP route. This decision process is fundamental to Cisco routing behavior and ensures consistent, predictable route selection.
A common exam trap is confusing administrative distance with metrics or prefix length. While metrics like EIGRP’s composite metric or OSPF’s cost influence path selection within the same protocol, AD is the primary factor when comparing routes from different protocols. Another trap is assuming that routes with the same prefix length cannot come from multiple protocols; in reality, routers often receive overlapping routes and must use AD to choose. Practically, understanding AD helps network engineers troubleshoot routing issues and optimize route selection in multi-protocol environments.
KKey Concepts to Remember
Administrative distance is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols.
A router selects the route with the lowest administrative distance when multiple protocols advertise the same destination prefix with identical prefix lengths.
EIGRP uses a default administrative distance of 90, which is lower and thus preferred over OSPF’s default administrative distance of 110.
Routing metrics influence path selection only within the same routing protocol, not across different protocols when administrative distance is compared.
Routers can receive overlapping routes from multiple protocols and use administrative distance to determine which route to install in the routing table.
Prefix length equality means the router cannot use longest prefix match to decide, so administrative distance becomes the deciding factor.
A lower administrative distance indicates a more trusted route source and leads to route preference in Cisco routing decisions.
→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 is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols.
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 is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — Administrative distance is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols..
What is the correct answer to this question?
The correct answer is: EIGRP — The EIGRP route is preferred because its administrative distance is lower. In practical terms, once the prefix length is the same, the router compares the trustworthiness of the route source. Lower administrative distance wins. Since 90 is lower than 110, EIGRP is preferred over OSPF for that destination.
This is an administrative-distance comparison question, not a longest-prefix question. The key is that the prefix length is equal, so source preference becomes the deciding factor.
What should I do if I get this 200-301 question wrong?
Review administrative distance is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Administrative distance is a Cisco router’s method to compare the trustworthiness of routes from different routing protocols.
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