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Question 840 of 1,052
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CCNA Practice Question: Which TWO statements correctly describe OSPFv2…
This 200-301 practice question tests your understanding of 200-301 exam topics. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO statements correctly describe OSPFv2 router-id selection and verification in a single-area configuration?
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
✓
When no 'router-id' is configured, a loopback interface with the highest IP address is preferred over a physical interface for the router-id.
The OSPF router-id is a 32-bit identifier used to uniquely identify a router. It is selected in the following order: 1) explicitly configured router-id via 'router-id' command, 2) highest loopback interface IP address, 3) highest active physical interface IP address. The 'show ip ospf' command displays the current router-id. Option D is correct because a loopback interface address is preferred over a physical interface address. Option E is correct because the 'show ip ospf' command is the primary verification tool. Option A is incorrect because the router-id is not derived from the MAC address. Option B is incorrect because changing the router-id requires a reload or a 'clear ip ospf process' command. Option C is incorrect because the router-id must be unique across the OSPF domain.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The OSPF router-id is automatically derived from the MAC address of the first Ethernet interface.
Why it's wrong here
The router-id is not derived from the MAC address.
- ✗
If the router-id is changed using the 'router-id' command, the change takes effect immediately without any additional action.
Why it's wrong here
Changing the router-id requires a reload or a 'clear ip ospf process' command to take effect.
- ✗
The router-id must be the same on all routers in a single OSPF area.
Why it's wrong here
The router-id must be unique within the OSPF domain.
- ✓
When no 'router-id' is configured, a loopback interface with the highest IP address is preferred over a physical interface for the router-id.
Why this is correct
Loopback interfaces are preferred due to their stability.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
The 'show ip ospf' command displays the current OSPF router-id.
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.
✓When no 'router-id' is configured, a loopback interface with the highest IP address is preferred over a physical interface for the router-id.Correct answer▾
Why this is correct
Loopback interfaces are preferred due to their stability.
✗The OSPF router-id is automatically derived from the MAC address of the first Ethernet interface.Wrong answer — click to see why▾
Why this is wrong here
The router-id is selected based on the highest IP address of a loopback or active physical interface, or an explicitly configured value.
✗If the router-id is changed using the 'router-id' command, the change takes effect immediately without any additional action.Wrong answer — click to see why▾
Why this is wrong here
The OSPF process must be reset for the new router-id to be used.
✗The router-id must be the same on all routers in a single OSPF area.Wrong answer — click to see why▾
Why this is wrong here
Each router must have a unique router-id to avoid adjacency issues.
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?”
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
Changing the router-id requires a reload or a 'clear ip ospf process' command to take effect.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 200-301 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 200-301 question test?
OSPF neighbours must agree on key parameters.
What is the correct answer to this question?
The correct answer is: When no 'router-id' is configured, a loopback interface with the highest IP address is preferred over a physical interface for the router-id. — The OSPF router-id is a 32-bit identifier used to uniquely identify a router. It is selected in the following order: 1) explicitly configured router-id via 'router-id' command, 2) highest loopback interface IP address, 3) highest active physical interface IP address. The 'show ip ospf' command displays the current router-id. Option D is correct because a loopback interface address is preferred over a physical interface address. Option E is correct because the 'show ip ospf' command is the primary verification tool. Option A is incorrect because the router-id is not derived from the MAC address. Option B is incorrect because changing the router-id requires a reload or a 'clear ip ospf process' command. Option C is incorrect because the router-id must be unique across the OSPF domain.
What should I do if I get this 200-301 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 200-301 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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