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300-410 Practice Question: Configures a DMVPN Phase 3 network with EIGRP and…
A network engineer configures a DMVPN Phase 3 network with EIGRP and uses the 'ip nhrp redirect' and 'ip nhrp shortcut' commands on the hub and spokes. Unexpectedly, spoke-to-spoke traffic still goes through the hub even after the shortcut is established, based on show ip nhrp shortcut output. Which is the most likely explanation?
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 EIGRP route to the remote spoke's network still has the hub as the next-hop with a lower metric than the NHRP shortcut, so the router prefers the hub path.
In DMVPN Phase 3, the shortcut is created when the spoke receives a redirect from the hub and sends a resolution request to the target spoke. However, for the shortcut to be used, the routing table must have a route that points to the shortcut next-hop. EIGRP, by default, installs routes with the hub as the next-hop. The corner case is that the spoke's routing table still prefers the hub as the next-hop because the EIGRP metric for the hub route is lower than the shortcut. The fix is to use 'ip nhrp shortcut' with 'ip nhrp redirect' and ensure that the routing protocol's metric is adjusted (e.g., using offset-list) or that the shortcut is installed with a better metric via NHRP.
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 EIGRP route to the remote spoke's network still has the hub as the next-hop with a lower metric than the NHRP shortcut, so the router prefers the hub path.
Why this is correct
The NHRP shortcut creates a host route or /32 route, but if the EIGRP route has a lower administrative distance or better metric, the router will use the hub path.
- ✗
The 'ip nhrp shortcut' command is not configured on the spoke's tunnel interface, so the shortcut is not used for forwarding.
Why it's wrong here
The engineer configured it, so it should be present.
- ✗
The NHRP redirect is not enabled on the hub, so the spoke never receives redirect messages to trigger shortcut creation.
Why it's wrong here
The engineer configured it, so redirects should be sent.
- ✗
The spoke's CEF is disabled, causing the shortcut to not be used in the forwarding path.
Why it's wrong here
CEF is typically enabled by default; disabling it would affect all forwarding, not just shortcuts.
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.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
DMVPN Phase 3
DMVPN Phase 3 is a Cisco networking technology that allows branch offices to connect directly to each other without always going through a central hub, but with smarter routing that lets the hub control the traffic paths more efficiently.
Key term
DMVPN Phase 2
DMVPN Phase 2 is an advanced Cisco routing technology that allows spoke routers to communicate directly with one another without sending traffic through a central hub, using dynamic routing protocols and multipoint GRE tunnels.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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