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 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
With BGP synchronisation enabled, iBGP-learned routes are not installed unless the same prefix exists in the IGP. The prefix sits in the BGP table but is withheld from the routing table until IGP convergence provides it.
- ✗
The next-hop-self command is missing on the iBGP peer.
Why it's wrong here
The stem states the next hop is reachable via an IGP, so next-hop-self is unnecessary; missing it would leave the next hop unreachable, not reachable. It is tempting because next-hop-self is a common iBGP fix, and would be correct if the advertised next hop were an unreachable external address.
- ✗
The prefix is filtered by an inbound route-map.
Why it's wrong here
An inbound route-map filtering the prefix would remove it from the BGP table entirely, yet the stem says the prefix appears there. It is tempting because inbound filtering is a frequent cause of missing routes, and would be correct if the prefix were absent from the BGP table rather than present.
- ✗
The maximum-paths limit is exceeded.
Why it's wrong here
Maximum-paths affects how many equal-cost paths are installed for a prefix already eligible; it does not prevent a single valid path from being selected. It is tempting because path-count limits do govern route installation, and would be correct if multiple equal-cost paths existed and only some were wanted.
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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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.