300-410 VPN Technologies Practice Question
A network administrator is troubleshooting a DMVPN Phase 3 network. Spokes register with the hub, and routing adjacencies are up. However, spoke-to-spoke traffic is not taking the optimal path; it still goes through the hub. The hub is configured with `ip nhrp redirect` and `ip nhrp map multicast dynamic`. The administrator verifies that the spokes have `ip nhrp shortcut` configured. What is the most likely cause?
⚠ Common exam trap
The trap here is assuming that `ip nhrp redirect` and `ip nhrp shortcut` alone are sufficient for spoke-to-spoke tunnels in Phase 3, while overlooking the need for specific routing information on 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
✓
The routing protocol is not advertising specific routes to the spokes.
In DMVPN Phase 3, the hub uses `ip nhrp redirect` to inform spokes of a better path, but spokes also need a specific route to the destination to trigger NHRP resolution. If the hub only advertises a default route or summary, spokes lack the specific route and continue forwarding through the hub. Advertising specific routes from the hub enables spokes to resolve next hops and build direct tunnels.
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 routing protocol is not advertising specific routes to the spokes.
Why this is correct
In DMVPN Phase 3, the hub must advertise specific routes (not just a default or summary) to the spokes so they can resolve next-hop addresses and build shortcuts. If the hub only advertises a default route, spokes will not have a specific route to trigger NHRP resolution. Ensuring the hub advertises specific routes allows shortcuts to form.
- ✗
The spokes are not configured with `ip nhrp redirect`.
Why it's wrong here
`ip nhrp redirect` is a hub-side command that instructs the hub to send redirect messages to spokes. Spokes do not need it; they need `ip nhrp shortcut` to act on redirects. Since the spokes already have shortcut configured, this is not the cause.
- ✗
The hub is not configured with `ip nhrp summary-map`.
Why it's wrong here
`ip nhrp summary-map` is used in DMVPN Phase 3 to allow the hub to advertise a summary route to the spokes, reducing routing table size. It is not required for spoke-to-spoke shortcut tunnels. The issue is that shortcuts are not being triggered, which is unrelated to summary mapping.
- ✗
The spokes are not configured with `ip nhrp network-id`.
Why it's wrong here
`ip nhrp network-id` is required for NHRP registration and must match on all routers. If it were missing, the spokes would not register with the hub, and routing adjacencies would not form. Since adjacencies are up, the network-id is correctly configured. This is not the cause of the shortcut failure.
Visual reference
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Related to this question
Learn chapter
ACL-Based Traffic Filtering and Policy-Based Routing
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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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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