300-410 Infrastructure Services Practice Question
A network engineer is troubleshooting a DMVPN Phase 3 network. Spoke-to-spoke tunnels are not being established directly; traffic between spokes is going through the hub. The hub is configured with 'ip nhrp redirect' and spokes with 'ip nhrp shortcut'. Which additional configuration is required on the spokes to enable direct spoke-to-spoke communication?
⚠ Common exam trap
The trap here is focusing on NHRP commands like 'ip nhrp redirect' and 'ip nhrp shortcut' while overlooking the routing table requirement for specific routes to trigger shortcut switching.
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
✓
Ensure that the spokes have a route to the destination spoke's tunnel network via the hub, and that they are not using a default route that prevents shortcut switching.
In DMVPN Phase 3, spoke-to-spoke shortcut tunnels require that the spoke has a specific route to the destination network pointing to the tunnel interface. If the spoke uses a default route, it will not perform NHRP resolution for the specific destination, and traffic will continue to flow through the hub. Therefore, ensuring that spokes have specific routes (not just a default) is essential for direct 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.
- ✗
Configure 'ip nhrp network-id' with the same value on all spokes and the hub.
Why it's wrong here
The 'ip nhrp network-id' must match on all DMVPN routers for them to form a single NBMA network. However, if it were mismatched, the spokes would not be able to register with the hub or establish any tunnels, including hub-to-spoke. Since hub-to-spoke tunnels are working (traffic goes through the hub), the network-id is likely correct. Thus, this is not the missing configuration for spoke-to-spoke.
- ✓
Ensure that the spokes have a route to the destination spoke's tunnel network via the hub, and that they are not using a default route that prevents shortcut switching.
Why this is correct
For spoke-to-spoke shortcut tunnels to form, the spoke must have a specific route to the destination network that points to the tunnel interface, not a default route. If a default route is used, the spoke will not attempt NHRP resolution for the specific destination and will continue sending traffic via the hub. The spoke needs a more specific route (e.g., a /24 for the remote spoke's LAN) to trigger the shortcut. This is a common oversight in DMVPN Phase 3 deployments.
- ✗
Configure 'ip nhrp shortcut' on the hub tunnel interface.
Why it's wrong here
The 'ip nhrp shortcut' command is typically configured on spokes, not the hub. It allows the spoke to use NHRP resolution to find a direct path to another spoke when it receives a redirect message. Configuring it on the hub would not help spoke-to-spoke communication and is not the intended design. The hub should have 'ip nhrp redirect' instead.
- ✗
Configure 'ip nhrp map multicast dynamic' on the hub tunnel interface.
Why it's wrong here
The 'ip nhrp map multicast dynamic' command allows the hub to dynamically learn multicast mappings for spokes, which is essential for routing protocols over DMVPN. However, it does not directly enable spoke-to-spoke shortcut tunnels. The issue described is that shortcut tunnels are not forming despite redirect and shortcut being configured. This command is typically already present on the hub for dynamic routing, but it is not the missing piece for spoke-to-spoke.
Go deeper
Related to this question
Learn chapter
BGP Route Selection and Policy
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 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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