Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
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 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
EIGRP
This is correct because EIGRP’s default administrative distance of 90 is lower than OSPF’s 110.
B
Distractor review
OSPF
This is wrong because OSPF’s administrative distance is higher in this comparison.
C
Distractor review
Both equally
This is wrong because the lower administrative distance is preferred.
D
Distractor review
Neither, because route sources cannot overlap
This is wrong because routers can compare and choose between multiple sources for the same prefix.
Common exam trap
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.
Technical deep dive
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.
- Understanding administrative distance helps network engineers troubleshoot routing conflicts and optimize multi-protocol routing environments.
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?
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?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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