300-410 Layer 3 Technologies Practice Question
A network engineer is troubleshooting a DMVPN Phase 3 network using OSPF. Spoke routers are unable to form OSPF adjacencies with each other directly, even though they can reach the hub. The engineer wants to enable direct spoke-to-spoke communication. Which configuration is required on the hub?
⚠ Common exam trap
A common mix-up: candidates confuse the roles of ip nhrp redirect and ip nhrp shortcut, placing shortcut on the hub instead of the spokes.
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
✓
ip nhrp redirect
In DMVPN Phase 3, the hub must have ip nhrp redirect to send redirect messages to spokes, enabling them to establish direct tunnels. Spokes require ip nhrp shortcut to act on those redirects. The other options are either configured on spokes or are basic NHRP settings not specific to enabling spoke-to-spoke communication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ip nhrp redirect
Why this is correct
In DMVPN Phase 3, the hub must be configured with ip nhrp redirect to send NHRP redirect messages to spokes when it receives traffic that could be sent directly between spokes. This allows the hub to inform the originating spoke of a better path, enabling direct spoke-to-spoke tunnels. Without this, spokes continue to route through the hub.
- ✗
ip nhrp shortcut
Why it's wrong here
ip nhrp shortcut is configured on spoke routers, not the hub. It allows the spoke to use NHRP redirect messages to create a shortcut path to another spoke. While essential for spoke-to-spoke communication, it is not the configuration required on the hub. The question asks for the hub configuration.
- ✗
ip nhrp map multicast dynamic
Why it's wrong here
ip nhrp map multicast dynamic is used on the hub in DMVPN Phase 1 or 2 to allow dynamic multicast mapping for routing protocols. In Phase 3, it is not the key command for enabling direct spoke-to-spoke communication; that is handled by NHRP redirect and shortcut. This command alone does not enable spoke-to-spoke tunnels.
- ✗
ip nhrp network-id 1
Why it's wrong here
ip nhrp network-id is a basic NHRP configuration that must match on all DMVPN routers. It identifies the NHRP network but does not enable spoke-to-spoke communication. It is required for NHRP to function, but it is not the specific command that triggers redirects or shortcuts.
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
DMVPN and FlexVPN Technologies
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.
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.
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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
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