![Understanding DMVPN Phase 1, 2, and 3: A Practical Guide [CCNP ENTERPRISE]](https://networkjourney.com/wp-content/uploads/2025/06/Understanding-DMVPN-Phase_networkjourney.png)
I’m here to help you simplify one of the most important VPN technologies used in scalable WAN deployments — Dynamic Multipoint VPN (DMVPN). Whether you’re a network engineer working on real-world WAN rollouts or preparing for your next professional certification, this guide will equip you with hands-on knowledge and EVE-NG labs to truly master DMVPN Phases 1, 2, and 3.
Let’s dive into the theory, differences, CLI, and lab configuration — all in one place!
Table of Contents
Theory in Brief: What is DMVPN?
DMVPN is a Cisco proprietary solution that simplifies VPN management by allowing direct communication between remote sites without having to form permanent static tunnels. It uses:
- mGRE (Multipoint GRE): For dynamic tunnel creation.
- NHRP (Next Hop Resolution Protocol): To map public IPs to private ones.
- IPSec: To encrypt tunnel traffic securely.
DMVPN is divided into three phases based on how traffic is handled and what routing protocols can be used.
DMVPN Phase 1: Hub-and-Spoke Only
- All traffic flows through the hub
- No direct spoke-to-spoke communication
- Static or dynamic routing at the hub
DMVPN Phase 2: Spoke-to-Spoke Dynamic Tunnels
- Allows direct spoke-to-spoke tunnels
- Routing protocol enabled (EIGRP/OSPF/BGP)
- Requires NHRP redirection
DMVPN Phase 3: Enhanced Routing with Spoke Shortcuts
- Uses route summarization with NHRP shortcuts
- More scalable and efficient
- Excellent for large-scale enterprise VPNs
DMVPN Phase Comparison
| Feature | Phase 1 | Phase 2 | Phase 3 |
|---|---|---|---|
| Spoke-to-Spoke Traffic | No | Yes | Yes |
| Routing Protocol | Static or Dynamic | Dynamic (No summarization) | Dynamic (Supports summarization) |
| NHRP Redirection | Not Required | Required | Required |
| Scalability | 2 | 3 | 4 |
| Use Case | Small Hub & Spoke VPN | Medium deployments | Large scale, dynamic networks |
CLI Commands (Common to All Phases)
| Task | IOS Command Example |
| Configure Tunnel Interface | interface Tunnel0 |
| Assign IP to Tunnel | ip address 10.1.1.1 255.255.255.0 |
| Set Tunnel Source/Destination | tunnel source Gig0/0 / tunnel mode gre multipoint |
| NHRP Mapping | ip nhrp map <tunnel-ip> <nbma-ip> |
| NHRP Network-ID | ip nhrp network-id 1 |
| Enable IPSec Protection Profile | tunnel protection ipsec profile dmvpn-profile |
Real-World Use Cases
| Scenario | Phase Used | Reason |
| Remote site access via HQ only | Phase 1 | Centralized control & logging |
| Branch-to-branch direct communication | Phase 2 | Efficient peer-to-peer VoIP/file sharing |
| Large enterprise with summarization | Phase 3 | Optimized routing & fewer routes in RIB |
EVE-NG LAB: DMVPN Phase 1 Topology
Diagram
Objective
Build a hub-and-spoke DMVPN topology using Phase 1 (hub routes all traffic).
Sample Configuration: Hub
interface Tunnel0 ip address 10.1.1.1 255.255.255.0 tunnel source Gig0/0 tunnel mode gre multipoint ip nhrp network-id 1 ip nhrp authentication dmvpn
Spoke Example
interface Tunnel0 ip address 10.1.1.2 255.255.255.0 tunnel source Gig0/0 tunnel destination <Hub-IP> ip nhrp network-id 1 ip nhrp authentication dmvpn ip nhrp map 10.1.1.1 <Hub-NBMA> ip nhrp map multicast <Hub-NBMA>
EVE-NG LAB: DMVPN Phase 2 with EIGRP
Objective
Enable direct spoke-to-spoke communication with routing protocol.
! Hub router eigrp 100 network 10.1.1.0 ! interface Tunnel0 ip nhrp redirect ! ! Spoke interface Tunnel0 ip nhrp shortcut router eigrp 100 network 10.1.1.0
EVE-NG LAB: DMVPN Phase 3 with Summarization
Objective
Configure Phase 3 with summarization and NHRP shortcuts.
interface Tunnel0 ip nhrp redirect ip summary-address eigrp 100 10.1.0.0 255.255.0.0 ! Spoke: ip nhrp shortcut
Use show dmvpn, show ip nhrp, and debug nhrp for validation.
Troubleshooting Tips
| Issue | Likely Cause | Solution |
| No tunnel form | Tunnel source or NHRP config missing | Verify interfaces and NHRP settings |
| Spokes not reaching each other | Phase mismatch or no redirection | Use correct DMVPN phase and configs |
| IPSec not forming | Profile misconfigured or not applied | Attach the correct IPSec profile |
| No EIGRP routes | Network mismatch or NHRP issue | Check routing and tunnel connectivity |
FAQs
1. Can I use OSPF instead of EIGRP in DMVPN?
Answer:
Yes, you can use OSPF with DMVPN, but EIGRP is generally preferred due to better compatibility with DMVPN’s dynamic behavior. Here’s why:
- EIGRP handles NBMA networks more efficiently.
- EIGRP does not rely on DR/BDR roles, unlike OSPF.
- EIGRP supports route summarization and stub routing more flexibly across phases.
In multi-hub or large-scale environments, EIGRP simplifies routing and reduces convergence issues.
2. Do spokes talk directly in DMVPN Phase 1?
Answer:
No, in Phase 1, all communication must go through the hub router. Spoke-to-spoke tunnels are not dynamically built.
- Only static point-to-multipoint tunnels exist.
- Spokes register with the hub using NHRP, but the hub forwards all traffic.
If you need direct spoke-to-spoke tunnels, consider upgrading to Phase 2 or Phase 3.
3. Is IPsec mandatory in DMVPN?
Answer:
Not strictly, but highly recommended.
- DMVPN without IPsec is functionally possible but insecure.
- In practice, most deployments use IPsec for encryption and integrity.
- IPsec protects traffic over the public internet or MPLS when data confidentiality is needed.
In Cisco IOS, IPsec integration with DMVPN is seamless using profile-based or tunnel protection configurations.
4. Why use DMVPN Phase 3 over Phase 2?
Answer:
DMVPN Phase 3 is preferred in large networks because it:
- Supports route summarization at the hub.
- Allows NHRP redirect/shortcut messages, enabling dynamic spoke-to-spoke tunnels even with summarized routes.
- Offers better scalability and improved control over routing paths.
Unlike Phase 2, Phase 3 avoids routing black holes when using summarization.
5. Can I simulate DMVPN in EVE-NG?
Answer:
Yes! DMVPN labs are fully supported in EVE-NG, provided you use:
- Cisco IOS routers (e.g., c7200, IOSv, CSR1000v)
- Images that support NHRP, IPsec, and routing protocols
Simulation tips:
- Use at least one hub and two spokes.
- Test Phase 1, 2, and 3 topologies with EIGRP and OSPF.
- Validate NHRP mappings and tunnel behavior using CLI tools.
6. How do I validate tunnel status in DMVPN?
Answer:
You can use the following CLI commands:
show dmvpn
Displays NHRP mappings, tunnel states, and peer status.
show crypto session
Validates IPsec tunnels (ISAKMP and IPsec SAs).
show ip nhrp
Lists resolved next-hop addresses and peer info.
These commands help diagnose tunnel issues and verify successful registration and encryption.
7. What is the role of NHRP in DMVPN?
Answer:
NHRP (Next Hop Resolution Protocol) is a core DMVPN component. It:
- Maps tunnel IPs to real (NBMA) IPs.
- Enables dynamic spoke registration to the hub.
- In Phase 2 and 3, it supports shortcuts between spokes using redirect messages.
In short, NHRP acts like ARP for tunnels and is essential for dynamic connectivity.
8. How does DMVPN handle failover?
Answer:
DMVPN supports multi-hub configurations, allowing:
- Primary/secondary hubs using dynamic NHRP registration priorities.
- Spokes to failover to a backup hub if the primary becomes unreachable.
Configuration Tip:
Use different tunnel source IPs and NHRP registrations for each hub.
You can also combine routing protocols (like EIGRP/OSPF) with tracking objects for seamless failover.
9. Can DMVPN work over LTE or Broadband?
Answer:
Yes, DMVPN works well over any IP-based transport, including:
- Broadband (Cable, DSL)
- 4G/5G LTE
- Public internet
Just ensure the devices:
- Can form public IP-based tunnels
- Allow UDP 500/4500 (for IPsec)
- Are NAT-T capable if NAT is involved
This makes DMVPN ideal for branch sites with unreliable or mobile WAN links.
10. What are the key differences among DMVPN Phases?
Answer:
Here’s a quick breakdown of the differences:
| Feature | Phase 1 | Phase 2 | Phase 3 |
|---|---|---|---|
| Spoke-to-Spoke Tunnels | No | Yes | Yes (optimized via redirect) |
| Routing Requirement | Hub-only routing | Full mesh routing required | Allows summarization |
| NHRP Shortcuts | No | Yes | Yes with redirection |
| Best for | Small/Hub-spoke setups | Mid-size networks | Large-scale, scalable designs |
Phase 3 is the most scalable and flexible — and widely used in production environments today.
Related YouTube Video
Watch the Complete CCNP Enterprise: Understanding DMVPN Phase 1, 2, and 3: A Practical Guide Lab Demo & Explanation on our channel:
Final Note
Understanding how to differentiate and implement Understanding DMVPN Phase 1, 2, and 3: A Practical Guide is critical for anyone pursuing CCNP Enterprise (ENCOR) certification or working in enterprise network roles. Use this guide in your practice labs, real-world projects, and interviews to show a solid grasp of architectural planning and CLI-level configuration skills.
If you found this article helpful and want to take your skills to the next level, I invite you to join my Instructor-Led Weekend Batch for:
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