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300-410 Practice Question: An engineer configures iBGP between two routers…
An engineer configures iBGP between two routers in the same AS. The BGP table shows the prefix, but it is not installed in the routing table. The next-hop is reachable via an IGP route. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the BGP synchronization rule as a subtle cause of routes being in the BGP table but not in the routing table, leading candidates to mistakenly focus on next-hop reachability or filtering issues.
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
✓
BGP synchronization is enabled, and the prefix is not present in the IGP.
When BGP synchronization is enabled, the router will not install an iBGP-learned prefix into the routing table unless the same prefix is also present in the IGP (e.g., OSPF or EIGRP). Since the next-hop is reachable via IGP but the prefix itself is not in the IGP, the synchronization rule blocks the route from being installed. This is a classic scenario where the BGP table shows the prefix, but it is missing from the routing table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
BGP synchronization is enabled, and the prefix is not present in the IGP.
Why this is correct
Correct. Synchronization prevents route installation if IGP does not have the prefix.
- ✗
The next-hop-self command is missing on the iBGP peer.
Why it's wrong here
Missing next-hop-self would cause unreachable next-hop, but next-hop is reachable.
- ✗
The prefix is filtered by an inbound route-map.
Why it's wrong here
Filtered prefix would not appear in BGP table.
- ✗
The maximum-paths limit is exceeded.
Why it's wrong here
Maximum-paths affects load balancing, not installation.
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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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.