mediumMultiple Choice
300-410 Practice Question: Which statement correctly describes the behavior…
Which statement correctly describes the behavior of the 'subnets' keyword when redistributing into OSPF?
⚠ Common exam trap
Watch out — candidates often confuse the default classful redistribution behavior with the effect of the 'subnets' keyword, leading candidates to select option A instead of B.
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
✓
It allows OSPF to redistribute subnetted routes in addition to classful networks.
The 'subnets' keyword in OSPF redistribution (e.g., 'redistribute connected subnets') instructs OSPF to include subnetted routes in the redistribution process. Without it, OSPF only redistributes classful network routes (major networks) and ignores any routes with a subnet mask longer than the classful default. This is a Cisco-specific behavior that ensures more specific routes are advertised into OSPF.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It causes OSPF to redistribute only classful network routes.
Why it's wrong here
'Subnets' does the opposite: without it OSPF redistributes only classful networks, and adding it advertises classless prefixes including their masks. It tempts because the keyword's absence genuinely produces classful-only redistribution, so the behaviour is easily inverted in recall.
- ✓
It allows OSPF to redistribute subnetted routes in addition to classful networks.
Why this is correct
The 'subnets' keyword removes OSPF's default classful redistribution restriction, permitting routes with non-classful masks to enter the domain. Without it, only networks matching their classful boundary are advertised. This satisfies the stem's requirement to redistribute subnetted routes alongside classful ones, which is essential in VLSM-addressed networks.
- ✗
It changes the metric of redistributed routes to the interface cost.
Why it's wrong here
The 'subnets' keyword controls which routes are advertised, permitting classless prefixes; it does not alter metric values, which redistribution metric-type or metric commands set. It tempts because interface cost is a real OSPF metric input, but it applies to default seed metrics, not this keyword.
- ✗
It is required only when redistributing BGP routes into OSPF.
Why it's wrong here
The subnets keyword is mandatory when redistributing any classful-routed protocol into OSPF, not just BGP, because OSPF needs the subnet mask attached to redistributed routes. It is tempting because BGP redistribution commonly pairs with it, but the requirement applies to all redistributed sources lacking mask information.
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.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 300-410 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 300-410 exam.