Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
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 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
The EIGRP route
This is correct because EIGRP's default administrative distance is lower than OSPF's.
B
Distractor review
The OSPF route
This is wrong because OSPF's default administrative distance is higher in this comparison.
C
Distractor review
Both routes are installed equally because the prefix length matches
This is wrong because equal prefix length alone does not make the routes equally preferred.
D
Distractor review
Neither route is used because protocols cannot advertise the same prefix
This is wrong because routers can receive the same prefix from multiple sources and choose one.
Common exam trap
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.
Technical deep dive
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.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
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 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?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
Discussion
Loading comments…
Sign in to join the discussion.