- A
The IS-IS route is a level 2 route, which has a default AD of 115, but the distance command only affects level 1 routes.
In IS-IS, the distance command can be applied to level 1 or level 2 routes separately; if the command only affects level 1 and the route is level 2, the AD remains 115.
- B
The OSPF route has a lower metric than the IS-IS route.
Why wrong: AD is compared before metric; if IS-IS AD is 105 and OSPF is 110, IS-IS is preferred regardless of metric.
- C
The distance command was applied under the OSPF process instead of IS-IS.
Why wrong: This would affect OSPF, not IS-IS, but the question states it was applied under IS-IS.
- D
The IS-IS route is redistributed from another protocol, so it has a higher default AD of 115.
Why wrong: Redistributed routes in IS-IS have AD 115 by default, but the distance command should still override it.
Quick Answer
The answer is that the distance command under the IS-IS process only affects Level 1 routes, not Level 2 routes. By default, IS-IS Level 2 routes have an administrative distance of 115, and the distance 105 ip 10.0.0.0 0.255.255.255 command will not override that value for a Level 2 route, leaving its AD unchanged at 115. Since OSPF’s default AD is 110, the OSPF route remains preferred. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of IS-IS route types and the granularity of the distance command—a common trap is assuming the command applies globally to all IS-IS routes. To fix this, you must either use the distance command with the level-2 keyword or adjust the OSPF distance. Memory tip: “Level 2 is left out—distance only drops Level 1 doubt.”
300-410 Administrative Distance Practice Question
This 300-410 practice question tests your understanding of administrative distance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is troubleshooting a route selection issue between two routing protocols. R1 learns the prefix 10.0.0.0/8 via both IS-IS (AD 115) and OSPF (AD 110). The engineer wants R1 to prefer the IS-IS route. After configuring the distance 105 ip 10.0.0.0 0.255.255.255 under the IS-IS process, the IS-IS route is still not preferred. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
The IS-IS route is a level 2 route, which has a default AD of 115, but the distance command only affects level 1 routes.
The distance command under IS-IS can set AD for specific routes. With the new AD of 105, IS-IS should be preferred over OSPF (AD 110). If it is not, either the command was not applied correctly (e.g., wrong ACL) or the OSPF AD was also lowered.
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 IS-IS route is a level 2 route, which has a default AD of 115, but the distance command only affects level 1 routes.
Why this is correct
In IS-IS, the distance command can be applied to level 1 or level 2 routes separately; if the command only affects level 1 and the route is level 2, the AD remains 115.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The OSPF route has a lower metric than the IS-IS route.
- ✗
The distance command was applied under the OSPF process instead of IS-IS.
Why it's wrong here
This would affect OSPF, not IS-IS, but the question states it was applied under IS-IS.
- ✗
The IS-IS route is redistributed from another protocol, so it has a higher default AD of 115.
Why it's wrong here
Redistributed routes in IS-IS have AD 115 by default, but the distance command should still override it.
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
Redistributed routes in IS-IS have AD 115 by default, but the distance command should still override it.
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 300-410 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Administrative Distance — This question tests Administrative Distance — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The IS-IS route is a level 2 route, which has a default AD of 115, but the distance command only affects level 1 routes. — The distance command under IS-IS can set AD for specific routes. With the new AD of 105, IS-IS should be preferred over OSPF (AD 110). If it is not, either the command was not applied correctly (e.g., wrong ACL) or the OSPF AD was also lowered.
What should I do if I get this 300-410 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 300-410 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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