hardMultiple Choice
300-410 Practice Question: An engineer configures AS path prepending on an…
An engineer configures AS path prepending on an eBGP route to influence inbound traffic. However, traffic from a specific iBGP neighbor still prefers the prepended path. What is the most likely explanation?
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 iBGP neighbor has 'bgp bestpath as-path ignore' configured, which ignores AS path length entirely.
AS path prepending normally increases the AS path length, and BGP does consider AS path length during best-path selection. However, if the iBGP neighbor has 'bgp bestpath as-path ignore' configured, it skips the AS path length step, so prepending will not be considered and that neighbor may prefer the prepended path based on other attributes such as local preference or IGP metric. Option A is incorrect because iBGP does not ignore AS path length by default.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AS path prepending only affects eBGP path selection; iBGP routers ignore AS path length when comparing paths from different eBGP routers.
Why it's wrong here
iBGP uses the IGP metric to the next hop, not AS path length, so prepending does not influence iBGP decisions.
- ✗
The prepending was applied with 'set as-path prepend last-as 1', which only prepends the last AS, not the full path.
Why it's wrong here
This would still affect eBGP, but iBGP still ignores AS path length.
- ✓
The iBGP neighbor has 'bgp bestpath as-path ignore' configured, which ignores AS path length entirely.
Why this is correct
This would make all paths equal, but the issue is that prepending is not considered.
- ✗
The prepending was done on a route reflector, and the client does not see the prepended AS path.
Why it's wrong here
Route reflectors pass the AS path unchanged, so the client would see it.
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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.