300-410 VPN Technologies Practice Question
A network administrator is deploying DMVPN Phase 3 with IKEv2 between a hub and two spokes. The hub is configured with a dynamic multipoint VPN tunnel and uses NHRP. Spoke1 can reach Spoke2 via the hub, but direct spoke-to-spoke communication fails. The administrator verifies that NHRP registrations are successful and that the hub has routes to both spokes. Which action is most likely to enable direct spoke-to-spoke communication?
⚠ Common exam trap
Many candidates confuse DMVPN Phase 2 and Phase 3 requirements; Phase 3 specifically needs NHRP redirect on the hub and NHRP shortcut on the spokes to enable direct spoke-to-spoke tunnels.
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
✓
Enable NHRP redirect on the hub and NHRP shortcut on the spokes.
In DMVPN Phase 3, direct spoke-to-spoke tunnels are established through NHRP. The hub must be configured with 'ip nhrp redirect' to send redirect messages to spokes, and each spoke must have 'ip nhrp shortcut' to intercept traffic and initiate NHRP resolution for the destination spoke. Without these, spokes will continue to forward traffic through the hub even though NHRP registrations succeed.
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 the hub as a route reflector for BGP.
Why it's wrong here
A route reflector is used in iBGP topologies to reduce full-mesh peering, but it does not enable direct spoke-to-spoke data forwarding. In DMVPN Phase 3, the hub already forwards routing information; the issue is likely NHRP resolution or tunnel protection. Route reflection alone will not create direct tunnels.
- ✗
Disable split horizon on the hub's tunnel interface.
Why it's wrong here
Split horizon is relevant for distance-vector routing protocols like EIGRP or RIP to prevent routing loops. While DMVPN often uses EIGRP, disabling split horizon on the hub is not the mechanism that enables direct spoke-to-spoke forwarding. NHRP and routing protocol next-hop preservation are the key factors.
- ✓
Enable NHRP redirect on the hub and NHRP shortcut on the spokes.
Why this is correct
DMVPN Phase 3 requires NHRP redirect on the hub to inform spokes of a better path, and NHRP shortcut on the spokes to dynamically create direct tunnels. Without these, spokes continue to route through the hub. Enabling both features allows the spoke to resolve the remote spoke's NBMA address and build a direct GRE tunnel.
- ✗
Configure the spokes to use the hub as the next-hop for all routes.
Why it's wrong here
This describes Phase 2 behavior where spokes have a default route or summarized route pointing to the hub, but direct spoke-to-spoke tunnels are still possible with NHRP. However, in Phase 3, the goal is to avoid forcing all traffic through the hub. Setting the hub as next-hop for all routes would actually prevent direct spoke-to-spoke communication by design.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
Go deeper
Related to this question
Learn chapter
DMVPN and FlexVPN Technologies
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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