- A
Configure passive-interface Lo0 under the OSPF process
Why wrong: Passive-interface only suppresses OSPF hello packets on the loopback; it does not prevent the loopback IP from being used in router-ID election. The highest loopback IP will still become the router-ID at next process restart.
- B
Configure a static router-id using the router-id command under the OSPF process
Explicitly setting the OSPF router-ID prevents the process from dynamically re-electing a new router-ID based on interface IPs. This guarantees a stable router-ID regardless of added loopbacks, avoiding adjacency resets.
- C
Set a higher OSPF priority on the router’s interfaces
Why wrong: OSPF priority is used only for Designated Router (DR) election on multi-access networks, not for router-ID selection. Changing priority will not influence the router-ID or prevent its dynamic change.
- D
Configure the OSPF area as a stub area
Why wrong: Stub areas limit LSA types but have no effect on router-ID selection or adjacency resets caused by router-ID change. The issue is purely a router-ID stability problem.
Quick Answer
The answer is to configure a static router-id using the router-id command under the OSPF process. This prevents OSPF router-id change disruption because OSPF dynamically selects the highest loopback IP, or the highest physical interface IP if no loopback exists, as its router-id; adding a new loopback triggers a re-election upon process restart, which resets all adjacencies. On the CCNA 200-301 v2 exam, this tests your understanding of OSPF neighbor stability and the router-id selection order—a common trap is assuming a loopback addition won’t cause disruption if the process isn’t restarted, but any OSPF restart re-evaluates the router-id. The static router-id command locks the value, making it immune to interface changes. Memory tip: “Static stops the swap”—tying the router-id to a fixed address ensures your neighbors never see a new identity.
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A network engineer adds a loopback interface Lo0 with IP address 172.16.0.1/32 to router R1. After restarting the OSPF process, the OSPF router-ID changes from 10.1.1.1 to 172.16.0.1, and the neighbor relationship with R2 resets. What should the technician do next to prevent this disruption the next time a loopback is added?
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
Configure a static router-id using the router-id command under the OSPF process
Configuring a static router-id under the OSPF process ensures the router-ID never changes due to interface IP changes or loopback additions. This directly addresses the root cause of the adjacency reset—dynamic router-ID re-election.
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.
- ✗
Configure passive-interface Lo0 under the OSPF process
Why it's wrong here
Passive-interface only suppresses OSPF hello packets on the loopback; it does not prevent the loopback IP from being used in router-ID election. The highest loopback IP will still become the router-ID at next process restart.
- ✓
Configure a static router-id using the router-id command under the OSPF process
- ✗
Set a higher OSPF priority on the router’s interfaces
Why it's wrong here
OSPF priority is used only for Designated Router (DR) election on multi-access networks, not for router-ID selection. Changing priority will not influence the router-ID or prevent its dynamic change.
- ✗
Configure the OSPF area as a stub area
Why it's wrong here
Stub areas limit LSA types but have no effect on router-ID selection or adjacency resets caused by router-ID change. The issue is purely a router-ID stability problem.
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.
✓Configure a static router-id using the router-id command under the OSPF processCorrect answer▾
Why this is correct
Explicitly setting the OSPF router-ID prevents the process from dynamically re-electing a new router-ID based on interface IPs. This guarantees a stable router-ID regardless of added loopbacks, avoiding adjacency resets.
✗Configure passive-interface Lo0 under the OSPF processWrong answer — click to see why▾
Why this is wrong here
Passive-interface does not influence router-ID selection, which is based solely on highest active loopback IP address at process initialization.
✗Set a higher OSPF priority on the router’s interfacesWrong answer — click to see why▾
Why this is wrong here
Confusing DR election parameters with router-ID election leads candidates to a parameter that is irrelevant to router-ID stability.
✗Configure the OSPF area as a stub areaWrong answer — click to see why▾
Why this is wrong here
Changing area type does not address router-ID fluctuation; it targets LSDB optimization, which is unrelated to the dynamic router-ID re-election after loopback addition.
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.
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?
IP Routing — This question tests IP Routing — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Configure a static router-id using the router-id command under the OSPF process — Configuring a static router-id under the OSPF process ensures the router-ID never changes due to interface IP changes or loopback additions. This directly addresses the root cause of the adjacency reset—dynamic router-ID re-election.
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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Last reviewed: Jun 14, 2026
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