- A
The engineer applied the distance bgp 20 200 200 command, which lowers eBGP AD but not iBGP.
Why wrong: This command only lowers the eBGP administrative distance to 20, not iBGP, so iBGP remains at default AD 200. It does not cause iBGP to be preferred over OSPF.
- B
The engineer applied the distance 150 0.0.0.0 255.255.255.255 under the OSPF process, raising OSPF AD to 150.
Why wrong: This command raises OSPF's AD to 150, but iBGP's AD remains 200. Since 150 < 200, OSPF is still preferred. This configuration does not cause iBGP to be used.
- C
The engineer applied the distance bgp 20 100 200 command, lowering iBGP AD to 100.
This command lowers iBGP's AD to 100 (the second parameter), which is less than OSPF's default AD of 110. Thus, iBGP becomes preferred and the network uses the iBGP route.
- D
The OSPF route is a type 5 LSA, which has a higher AD than type 3 LSAs.
Why wrong: The type of OSPF LSA (type 3 vs type 5) does not affect administrative distance; AD is a property of the routing protocol, not the LSA type.
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. A key principle to apply: administrative Distance. 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.
An engineer is troubleshooting a network where R1 and R2 are running iBGP, and R1 learns the prefix 192.168.1.0/24 from R2 with an AD of 200. R1 also learns the same prefix via OSPF from R3 with AD 110. The engineer notices that R1 uses the iBGP route. What configuration change would cause this?
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 engineer applied the distance bgp 20 100 200 command, lowering iBGP AD to 100.
Only Option C correctly makes the iBGP route preferred by lowering the iBGP administrative distance to 100, which is less than OSPF's default AD of 110. Option B raises OSPF's AD to 150, but since iBGP's AD remains 200, OSPF (150) is still preferred over iBGP (200). Option A lowers eBGP AD, which does not affect iBGP. Option D is false because OSPF LSA type does not change AD.
Key principle: Administrative Distance
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 engineer applied the distance bgp 20 200 200 command, which lowers eBGP AD but not iBGP.
Why it's wrong here
This command only lowers the eBGP administrative distance to 20, not iBGP, so iBGP remains at default AD 200. It does not cause iBGP to be preferred over OSPF.
- ✗
The engineer applied the distance 150 0.0.0.0 255.255.255.255 under the OSPF process, raising OSPF AD to 150.
- ✓
The engineer applied the distance bgp 20 100 200 command, lowering iBGP AD to 100.
- ✗
The OSPF route is a type 5 LSA, which has a higher AD than type 3 LSAs.
Why it's wrong here
The type of OSPF LSA (type 3 vs type 5) does not affect administrative distance; AD is a property of the routing protocol, not the LSA type.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common trap is assuming that raising OSPF AD to any value above its default (110) will make iBGP preferred, but the modified OSPF AD (150) must exceed iBGP's AD (200) to have that effect. In this scenario, 150 is still lower than 200, so OSPF remains preferred.
Trap categories for this question
Command / output trap
This command only lowers the eBGP administrative distance to 20, not iBGP, so iBGP remains at default AD 200. It does not cause iBGP to be preferred over OSPF.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Administrative Distance
- iBGP
- OSPF
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Administrative Distance
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.
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.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
Administrative Distance — This question tests Administrative Distance — Administrative Distance.
What is the correct answer to this question?
The correct answer is: The engineer applied the distance bgp 20 100 200 command, lowering iBGP AD to 100. — Only Option C correctly makes the iBGP route preferred by lowering the iBGP administrative distance to 100, which is less than OSPF's default AD of 110. Option B raises OSPF's AD to 150, but since iBGP's AD remains 200, OSPF (150) is still preferred over iBGP (200). Option A lowers eBGP AD, which does not affect iBGP. Option D is false because OSPF LSA type does not change AD.
What should I do if I get this 300-410 question wrong?
Review administrative Distance, then practise related 300-410 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Administrative Distance
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Last reviewed: Jun 18, 2026
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