Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
An OSPF-enabled router has two paths to the same destination network, and both paths have the same OSPF cost. What is the most likely default behavior?
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
Install both routes and use equal-cost multipath forwarding
This is correct because OSPF can install multiple equal-cost paths to the same destination.
B
Distractor review
Discard both routes because OSPF cannot handle duplicates
This is wrong because OSPF can use multiple equal-cost routes.
C
Distractor review
Always keep only the route learned first
This is wrong because equal-cost multipath behavior is possible and common.
D
Distractor review
Replace both routes with a default route
This is wrong because there is no need to prefer a default route over valid equal-cost specific routes.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is believing that OSPF must select only one best route when multiple paths have the same cost. Many candidates mistakenly think OSPF discards duplicates or keeps only the first learned route. This misunderstanding leads to incorrect answers suggesting route discarding or default route replacement. The trap arises because some routing protocols or older implementations do not support equal-cost multipath. However, OSPF explicitly supports installing multiple equal-cost routes to improve load balancing and fault tolerance, so assuming otherwise causes errors in exam scenarios.
Technical deep dive
How to think about this question
OSPF (Open Shortest Path First) is a link-state routing protocol that calculates the best path to a destination based on the cumulative cost metric, which is derived from the bandwidth of each link along the route. The cost is inversely proportional to bandwidth, meaning higher bandwidth links have lower cost values. When a router receives multiple OSPF routes to the same destination, it compares the total cost of each path to determine the best route. If OSPF finds two or more paths with exactly the same cost, it installs all these equal-cost routes into the routing table. This behavior is known as equal-cost multipath (ECMP) forwarding. ECMP allows the router to forward packets over multiple paths simultaneously, effectively balancing the traffic load and providing redundancy. Cisco routers typically support up to four or more ECMP routes by default, depending on the platform and configuration. A common exam trap is assuming that OSPF will only keep one route and discard the others when multiple equal-cost paths exist. In reality, OSPF’s design encourages using all equal-cost paths to optimize network utilization and resilience. This behavior contrasts with protocols or scenarios where only a single best route is chosen. Understanding ECMP is critical for CCNA candidates because it affects how traffic is distributed and how routing tables are populated in OSPF-enabled networks.
KKey Concepts to Remember
- OSPF selects routes based on the lowest cumulative cost metric calculated from interface bandwidth values along the path.
- When OSPF discovers multiple paths with the same cost to a destination, it installs all equal-cost routes into the routing table for load balancing.
- Equal-cost multipath (ECMP) forwarding allows OSPF routers to distribute traffic evenly across multiple paths with identical metrics to improve bandwidth utilization and redundancy.
- OSPF does not discard routes simply because duplicates exist; it prefers to use all equal-cost routes rather than choosing only one.
- The OSPF routing process compares path costs and installs multiple routes only if their costs are exactly equal according to OSPF’s metric calculation.
- OSPF’s ability to install multiple equal-cost routes contrasts with some protocols that only select a single best path based on administrative distance or metric.
- Routers performing ECMP use per-packet or per-flow load balancing methods to forward traffic across equal-cost paths without causing routing loops.
- OSPF’s metric is based on bandwidth, so paths with different bandwidths will have different costs, preventing ECMP unless costs match exactly.
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?
OSPF selects routes based on the lowest cumulative cost metric calculated from interface bandwidth values along the path.
What is the correct answer to this question?
The correct answer is: Install both routes and use equal-cost multipath forwarding — When OSPF learns two equally good paths to the same destination, the router can install both and perform equal-cost multipath forwarding. In plain language, the router does not have to throw one away simply because there are two valid answers. If the routes are truly equal from OSPF’s perspective, it can use both paths to improve resilience and share traffic. This is a classic routing behavior question because many candidates assume the router must always choose only one best path. In reality, equal-cost multipath is a normal feature in many routing environments. The key is that the paths must be equally good according to the protocol’s metric logic.
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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