CCNA IP Routing Practice Question
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?
⚠ Common exam trap
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.
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
✓
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.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Install both routes and use equal-cost multipath forwarding
Why this is correct
OSPF is a link-state protocol that computes the shortest path tree using Dijkstra's algorithm, and when two or more paths to a destination have identical metrics, it intentionally installs them all as equal-cost multipath routes. These parallel next hops are placed in the routing table, and Cisco IOS uses CEF to load-balance traffic across them, maximizing bandwidth utilization and providing fast failover if one link goes down.
- ✗
Discard both routes because OSPF cannot handle duplicates
Why it's wrong here
OSPF does not treat multiple equal-cost paths as duplicates to be discarded; instead, the SPF calculation is specifically designed to recognize and preserve all viable equal-cost routes. Distinct next hops to the same prefix are not an error condition, and OSPF's link-state database inherently supports such topologies without any duplication conflict. Throwing away both routes would be destructive and would violate OSPF's fundamental multipath capability.
When this WOULD be correct
In a hypothetical exam scenario where the question specifies that OSPF is configured to only allow unique routes and duplicates are filtered out, option B would be correct. For example, if the question states that 'OSPF is configured with a unique route filter,' then discarding duplicates would be the expected behavior.
- ✗
Always keep only the route learned first
Why it's wrong here
Keeping only the route learned first is a misconception that confuses OSPF's deterministic SPF computation with hop-by-hop distance-vector behavior. OSPF does not track arrival order of routes; it calculates the entire topology and selects routes based on metric alone, and it can select multiple equal-cost paths simultaneously. By installing only one path, the router would waste available bandwidth and lose redundancy, which directly contradicts OSPF's design goal of efficient, loop-free multipath routing.
When this WOULD be correct
In a different scenario where a routing protocol only allows a single route to a destination, such as a legacy protocol that does not support multipath routing, the question might ask what happens when two routes are learned, leading to the correct answer being to keep only the first learned route.
- ✗
Replace both routes with a default route
Why it's wrong here
Replacing valid equal-cost specific routes with a default route would discard the more specific, directly computed paths and send traffic through a less optimal gateway. OSPF always prefers the longest prefix match, so a specific route to the destination is chosen over a default route, regardless of whether multiple equal-cost specifics exist. Also, a default route is typically injected into OSPF only by an ASBR or via configuration, not automatically generated just because parallel paths are present.
When this WOULD be correct
In a different scenario, if the question specified that OSPF was configured to use a default route for all traffic due to specific routing policies or if the network was designed to only allow a default route for redundancy, then this option could 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.
✓Install both routes and use equal-cost multipath forwardingCorrect answer▾
Why this is correct
OSPF is a link-state protocol that computes the shortest path tree using Dijkstra's algorithm, and when two or more paths to a destination have identical metrics, it intentionally installs them all as equal-cost multipath routes. These parallel next hops are placed in the routing table, and Cisco IOS uses CEF to load-balance traffic across them, maximizing bandwidth utilization and providing fast failover if one link goes down.
✗Discard both routes because OSPF cannot handle duplicatesWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPF can handle multiple equal-cost paths and does not discard routes simply due to duplication. Instead, it installs both routes for load balancing.
★ When this WOULD be the correct answer
In a hypothetical exam scenario where the question specifies that OSPF is configured to only allow unique routes and duplicates are filtered out, option B would be correct. For example, if the question states that 'OSPF is configured with a unique route filter,' then discarding duplicates would be the expected behavior.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of OSPF's capabilities, thinking that it cannot manage multiple paths to the same destination, leading to the assumption that duplicates must be discarded.
✗Always keep only the route learned firstWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPF is designed to support equal-cost multipath routing; it does not discard routes simply because they were learned at different times. Both routes would be installed in the routing table if they have the same cost.
★ When this WOULD be the correct answer
In a different scenario where a routing protocol only allows a single route to a destination, such as a legacy protocol that does not support multipath routing, the question might ask what happens when two routes are learned, leading to the correct answer being to keep only the first learned route.
Why candidates choose this
Candidates may find this option tempting due to a misunderstanding of OSPF's capabilities, mistakenly believing that it cannot handle multiple routes to the same destination, leading them to choose the option that suggests discarding duplicates.
✗Replace both routes with a default routeWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPF does not replace multiple equal-cost routes with a default route; it can use multiple paths for load balancing instead. The default behavior in OSPF is to install all equal-cost routes in the routing table.
★ When this WOULD be the correct answer
In a different scenario, if the question specified that OSPF was configured to use a default route for all traffic due to specific routing policies or if the network was designed to only allow a default route for redundancy, then this option could be correct.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of OSPF's behavior with multiple routes, confusing it with other routing protocols that may discard routes in favor of a default route under certain conditions.
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
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
Key term
OSPF
OSPF is a link-state routing protocol used to find the best path for data packets to travel across IP networks, like a smart GPS that recalculates routes when traffic changes.
Key term
Metric
A metric is a quantifiable measurement used to assess the performance, health, or status of IT systems, networks, or applications.
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JA
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.