hardMultiple Choice
300-410 Practice Question: An engineer configures iBGP between two routers…
An engineer configures iBGP between two routers in the same AS. The engineer notices that routes learned from one iBGP neighbor are not being advertised to another iBGP neighbor, even though the next-hop is reachable. The engineer verifies that the BGP session is established and that the routes are present in the BGP table. Which is the most likely explanation?
⚠ Common exam trap
300-410 often tests the iBGP split-horizon rule: candidates may incorrectly blame next-hop reachability or synchronization, but the core issue is that iBGP does not re-advertise routes learned from other iBGP peers.
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
✓
iBGP split-horizon rule prevents advertising iBGP-learned routes to other iBGP neighbors
The most likely explanation is the iBGP split-horizon rule, which states that routes learned from an iBGP neighbor are not advertised to other iBGP neighbors. This is a fundamental rule to prevent routing loops within an AS. Therefore, even though the next-hop is reachable and the session is established, the route will not be propagated to another iBGP peer unless a route reflector or full mesh is used.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
iBGP split-horizon rule prevents advertising iBGP-learned routes to other iBGP neighbors
Why this is correct
iBGP enforces split-horizon: a route learned from one iBGP peer is never re-advertised to another iBGP peer within the same AS. This prevents loops, so the second neighbour receives nothing. Routes must be reflected or confederated to propagate.
- ✗
The next-hop-self command is required for iBGP
Why it's wrong here
Next-hop-self changes the advertised next-hop for eBGP-learned routes, and the stem already states the next-hop is reachable, so it cannot explain the suppression. It is tempting because next-hop reachability is a frequent iBGP issue, but that condition is satisfied here, leaving the split-horizon rule as the actual cause.
- ✗
The BGP synchronization rule is enabled
Why it's wrong here
BGP synchronisation blocks iBGP-learned routes from being advertised until they are confirmed via IGP, matching the described behaviour. It is tempting because it is a legacy loop-prevention rule, but it is disabled by default on modern Cisco IOS, so its presence would be unusual unless explicitly configured.
- ✗
The routes are not valid because the next-hop is not reachable
Why it's wrong here
The stem explicitly states the next-hop is reachable, so validity is not the cause; routes are present in the BGP table. Next-hop reachability would be the explanation only if the advertising router's next-hop address were unresolvable in the IGP, which the scenario rules out.
Go deeper
Related to this question
Learn chapter
BGP Basics and Neighbor Relationships
Key term
BGP Route Reflector
A BGP Route Reflector is a networking device that reduces the number of BGP peer connections needed in a large network by allowing routers to share routing information without needing to connect to every other router directly.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.