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300-410 Practice Question: Is troubleshooting a BGP peering issue between…
A network engineer is troubleshooting a BGP peering issue between two directly connected routers, R1 and R2. R1 is configured with 'neighbor 10.1.1.2 remote-as 65002' and 'neighbor 10.1.1.2 update-source Loopback0', while R2 uses 'neighbor 10.1.1.1 remote-as 65001' and 'neighbor 10.1.1.1 update-source Loopback0'. The loopback interfaces are not advertised into any IGP, and there is no static route for the loopback addresses. The BGP session remains in Idle state. What is the most likely cause?
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 BGP session is stuck in Idle because the neighbor statements reference loopback interfaces that are not reachable.
BGP requires reachability to the neighbor's update-source address. Since the loopback addresses are not reachable via any routing protocol or static route, the TCP connection fails, keeping the session in Idle state.
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 BGP session is stuck in Idle because the neighbor statements reference loopback interfaces that are not reachable.
Why this is correct
Correct because BGP uses the update-source address for peering; without reachability, TCP cannot establish.
- ✗
The BGP session is stuck in Idle because the remote-as values are mismatched.
Why it's wrong here
Incorrect because the remote-as values match the configured AS numbers; this is not the issue.
- ✗
The BGP session is stuck in Idle because the update-source command is not allowed on directly connected interfaces.
Why it's wrong here
Incorrect because update-source can be used on any interface, including loopbacks, but requires reachability.
- ✗
The BGP session is stuck in Idle because the neighbor statements must use the directly connected interface IP addresses.
Why it's wrong here
Incorrect because BGP can peer using loopback addresses, but the loopbacks must be reachable.
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.