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300-410 Practice Question: Is troubleshooting an IPv6 connectivity issue on…
A network engineer is troubleshooting an IPv6 connectivity issue on a router that is receiving routes via EIGRP for IPv6. The engineer notices that some routes are not being installed in the routing table, even though the EIGRP neighbor relationship is established. The engineer checks the interface configuration and finds an inbound IPv6 ACL that permits only certain EIGRP packets. The ACL permits EIGRP hello packets and updates, but not EIGRP queries or replies. What is the most likely cause of the missing routes?
⚠ Common exam trap
Cisco often tests the misconception that only hello and update packets are needed for EIGRP route installation, but the trap here is that query and reply packets are essential for DUAL convergence and route installation, even when neighbors are up.
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 ACL is blocking EIGRP query and reply packets, which are necessary for the EIGRP process to install routes.
EIGRP for IPv6 uses multicast address FF02::A for all EIGRP packets, including hello, update, query, and reply. The ACL permits only hello and update packets, blocking query and reply packets. EIGRP requires query and reply packets for the Diffusing Update Algorithm (DUAL) to converge and install routes; without them, the router cannot complete the route installation process, even though the neighbor relationship is established.
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 ACL is blocking EIGRP query and reply packets, which are necessary for the EIGRP process to install routes.
Why this is correct
Correct because EIGRP queries and replies are used to ensure route consistency and convergence; blocking them can prevent route installation.
- ✗
The EIGRP router ID is not configured.
Why it's wrong here
Incorrect because the neighbor relationship is established, indicating the router ID is valid.
- ✗
The ACL is applied outbound, blocking the EIGRP updates from being sent.
Why it's wrong here
Incorrect because the ACL is inbound, as stated.
- ✗
The EIGRP for IPv6 is not enabled on the interface.
Why it's wrong here
Incorrect because the neighbor relationship is established, meaning EIGRP is enabled.
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.