300-410 Layer 3 Technologies Practice Question
A network engineer is deploying DMVPN Phase 3 with EIGRP as the routing protocol over a hub-and-spoke topology. The hub router is configured with `ip nhrp redirect` on its tunnel interface, and each spoke has `ip nhrp shortcut`. A spoke needs to send traffic to a remote subnet behind another spoke. Which mechanism allows the spoke to install a direct route to the remote spoke's tunnel IP without traversing the hub for every packet?
⚠ Common exam trap
The trap here is assuming that ICMP redirect or a hub-advertised host route can trigger spoke-to-spoke path optimization, when DMVPN specifically relies on NHRP redirect and NHRP resolution to build shortcut entries.
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
✓
NHRP resolution request triggered by the hub's redirect message, followed by installation of a shortcut entry in the NHRP cache and a /32 route in the RIB.
In DMVPN Phase 3, the hub uses NHRP redirect to tell a spoke that a better path exists. The spoke then sends an NHRP resolution request for the destination, receives the remote spoke's NBMA address, installs a shortcut entry, and creates a /32 route. This enables direct spoke-to-spoke forwarding without hairpinning through the hub for every packet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
NHRP resolution request triggered by the hub's redirect message, followed by installation of a shortcut entry in the NHRP cache and a /32 route in the RIB.
Why this is correct
With NHRP redirect on the hub, the hub sends an NHRP redirect message to the originating spoke when it forwards traffic out the same tunnel interface. The spoke then sends an NHRP resolution request for the destination NBMA address, receives a resolution reply, installs a shortcut entry in the NHRP cache, and the routing protocol (or NHRP) installs a /32 route, enabling direct spoke-to-spoke forwarding.
- ✗
The hub advertises a host route for each spoke's tunnel IP, and the spoke uses that route with the hub as next hop until the NHRP cache is populated by regular traffic.
Why it's wrong here
Advertising host routes for tunnel IPs does not create spoke-to-spoke shortcuts. The hub would still be the next hop, so traffic remains hairpinned. NHRP shortcut switching requires the spoke to resolve the remote spoke's NBMA address and install a shortcut entry; simply having a host route via the hub does not trigger that resolution or bypass the hub.
- ✗
The hub sends an ICMP redirect to the spoke, which then uses the hub's next-hop IP as the gateway for the remote subnet.
Why it's wrong here
ICMP redirects are not used by DMVPN to signal spoke-to-spoke path optimization. DMVPN uses NHRP redirect messages, which are a distinct NHRP protocol message type, not ICMP. Relying on ICMP redirect would leave traffic hairpinned through the hub and would not create the necessary NHRP shortcut entry or /32 route for direct forwarding.
- ✗
The spoke performs a recursive lookup on the hub's public IP and automatically derives the remote spoke's tunnel IP from the hub's NHRP database.
Why it's wrong here
A spoke cannot derive another spoke's tunnel IP from the hub's NHRP database without an explicit NHRP resolution exchange. The hub's NHRP database is not replicated to spokes. The spoke must send an NHRP resolution request for the remote spoke's NBMA address, which is triggered by the hub's redirect, not by recursive lookup on the hub's public IP.
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.
Go deeper
Related to this question
Learn chapter
Advanced EIGRP Features (Stub, Load Balancing, Named Mode)
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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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.