mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting a BGP route reachability issue
A network engineer is troubleshooting a BGP route reachability issue. R1 learns the prefix 10.1.1.0/24 via eBGP from R2 with an AD of 20, and via OSPF from R3 with an AD of 110. The engineer notices that R1 installs the OSPF route in the routing table instead of the eBGP route, even though the eBGP route is preferred by default. What is the most likely cause of this behavior?
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 distance bgp 20 200 200 command is configured under the BGP process, increasing the AD of eBGP routes to 200.
The default administrative distance for eBGP is 20, and for OSPF is 110, so eBGP should be preferred. However, if the distance command is applied to the eBGP neighbor or the BGP process, it can increase the AD of eBGP routes, making them less preferred than 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.
- ✗
The OSPF route has a lower metric than the eBGP route.
Why it's wrong here
Administrative distance is compared before metric; eBGP AD 20 is lower than OSPF AD 110 regardless of metric.
- ✓
The distance bgp 20 200 200 command is configured under the BGP process, increasing the AD of eBGP routes to 200.
Why this is correct
This command sets the AD for eBGP routes to 200, making OSPF (AD 110) preferred.
- ✗
The OSPF route is an inter-area route, which has a lower AD than intra-area routes.
Why it's wrong here
OSPF AD is fixed at 110 for all OSPF routes unless modified; inter-area does not change AD.
- ✗
The eBGP route is not the best path because the next-hop is unreachable.
Why it's wrong here
If the next-hop were unreachable, the route would not be installed at all, but the symptom states the OSPF route is installed, not that eBGP is missing.
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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Same concept, more angles
2 more ways this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer is troubleshooting a multi-homed BGP setup. R1 receives the prefix 10.1.1.0/24 from two eBGP peers: R2 (AS 100) and R3 (AS 200). The engineer configures the distance bgp 20 20 20 command on R1 to make all BGP routes have the same AD. However, R1 still prefers the route from R2 over R3. What is the most likely reason?
hard- A.The route from R2 has a lower MED than the route from R3.
- ✓ B.The route from R2 has a higher local preference than the route from R3.
- C.The route from R2 is the oldest BGP route.
- D.The AS path for the route from R2 is shorter than that from R3.
Why B: The distance bgp command sets AD for eBGP, iBGP, and local routes. With AD equal, the router uses other BGP path attributes, such as local preference, AS path length, or MED. The most common tie-breaker is local preference (default 100) or the oldest route.
Variation 2. 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?
medium- A.The engineer applied the distance bgp 20 200 200 command, which lowers eBGP AD but not iBGP.
- B.The engineer applied the distance 150 0.0.0.0 255.255.255.255 under the OSPF process, raising OSPF AD to 150.
- ✓ C.The engineer applied the distance bgp 20 100 200 command, lowering iBGP AD to 100.
- D.The OSPF route is a type 5 LSA, which has a higher AD than type 3 LSAs.
Why C: 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.