mediumMultiple Choice
CCNP Practice Question: An engineer is configuring a FlexVPN…
An engineer is configuring a FlexVPN hub-and-spoke network. The hub router has a loopback0 with IP 10.0.0.1/32. The spokes are configured to use IKEv2 with certificates. The engineer notices that the spokes can establish the IKEv2 tunnel and can ping the hub's tunnel IP, but cannot reach the loopback0 address. The hub has a static route for the spoke subnets. What is the most likely issue?
⚠ Common exam trap
Cisco often tests the distinction between tunnel reachability (IKEv2 and tunnel interface up) and routing reachability (prefixes advertised over the tunnel), leading candidates to incorrectly focus on IKEv2 or certificate issues when the tunnel is already established.
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 loopback0 is not advertised in the routing protocol.
The spokes can establish the IKEv2 tunnel and ping the hub's tunnel IP, confirming that the tunnel interface is up and the IKEv2 session is functional. However, the loopback0 address (10.0.0.1/32) is not reachable from the spokes because it is not advertised into the routing protocol (e.g., OSPF, EIGRP, or BGP) used over the FlexVPN tunnel. Without a route to the loopback0 prefix, the spokes' traffic to 10.0.0.1 is dropped by the hub's routing table, even though the tunnel is operational.
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 IKEv2 proposal does not match between hub and spoke.
Why it's wrong here
An IKEv2 proposal mismatch between hub and spoke would prevent the IKE SA and IPsec SA from ever being negotiated, so the tunnel would not initialize and the spoke would not be able to ping even the hub's tunnel IP. Since the tunnel is already established and the spoke can ping the tunnel interface, the IKE proposal must have matched successfully, and this cannot explain why the loopback is unreachable.
- ✗
The certificate authority is not trusted by the hub.
Why it's wrong here
In a certificate-based DMVPN, the hub must validate the spoke's certificate against a trusted root CA during IKEv2 authentication. If the CA were not trusted, certificate chain validation would fail, IKE_AUTH would be rejected, and the tunnel would never come up. Because the tunnel is operational and the spoke can ping the tunnel IP, the hub already trusts the CA, so this is not the cause of the loopback reachability problem.
- ✗
The tunnel interface is not in an up/up state.
Why it's wrong here
The tunnel interface being up/up indicates that the tunnel-protocol layer (e.g., GRE) and the underlying physical transport are functioning correctly. If the tunnel interface were down, the spoke could not ping the tunnel IP at all, because the interface would not process IP traffic. The fact that the tunnel IP responds proves the interface is up; this isolates the failure to the routing/route-propagation layer rather than the interface state.
- ✓
The loopback0 is not advertised in the routing protocol.
Why this is correct
The correct cause is that the hub's loopback0 network is not being advertised to the spokes by the dynamic routing protocol (such as EIGRP or OSPF) running over the DMVPN tunnel. Even though the tunnel is up and the tunnel IP is reachable, the spokes have no routing entry for the loopback0 prefix, so packets destined to that loopback are dropped or sent toward some default route. The fix is to include loopback0 in the routing protocol's network statements and ensure it is advertised through the tunnel, not just the tunnel interface itself.
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 350-401 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 350-401 exam.