Dual Hub Dual DMVPN Setup: Comparing Old vs New Cisco IOS Versions

🌐 Dual Hub Dual DMVPN – A Practical, Story-Driven Guide

Imagine your enterprise network as a transportation system.

You don’t want just one highway (hub)… because if it fails, everything stops.

So you build two highways, and every branch office (spoke) can use both.

That’s exactly what Dual Hub Dual DMVPN does.

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📚 Table of Contents

• Architecture Explained
• Routing Decision Logic (Simple Math)
• Challenges in Old IOS
• Modern IOS Improvements
• Configuration Example
• CLI Output
• Best Practices
• Key Takeaways
• Related Articles

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🏗️ Architecture Explained

• Two hubs → Hub1 & Hub2
• Two DMVPN clouds
• Each spoke connects to both hubs

👉 Result: Redundancy + Load balancing + Better control

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📐 Routing Logic (Made Simple)

Routing decisions depend on metrics like delay, bandwidth, or cost.

Example (EIGRP Metric)

\[ Metric = \frac{10^7}{Bandwidth} + Delay \]

Lower metric = preferred path.

👉 If Hub1 has lower delay → traffic goes to Hub1 👉 If Hub1 fails → Hub2 takes over

Failover Logic

\[ Primary < Secondary \]

When primary path fails:

\[ Traffic \rightarrow Backup\ Hub \]

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⚠️ Challenges in Older Cisco IOS

• High CPU usage (GRE + IPsec)
• Manual routing tweaks
• Complex configs
• Limited security features

Old CLI Example

interface Tunnel0
 ip nhrp map ...
 ip nhrp nhs ...

interface Tunnel1
ip nhrp map ...
ip nhrp nhs ... 

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🚀 Cisco IOS 15.9(3)M10+ Improvements

• Better encryption performance 🔐
• Faster convergence ⚡
• Smarter routing (EIGRP stub)
• Simplified QoS 🎯
• IKEv2 support

👉 Less manual work, more automation

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⚙️ Configuration Example (Modern)

interface Tunnel0 ip address 10.0.0.1 255.255.255.0 tunnel source Gig0/0 tunnel mode gre multipoint ip nhrp network-id 1 ip nhrp nhs 10.0.0.254

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🖥️ CLI Output

Show DMVPN Status

Router#show dmvpn

Tunnel0, Type:Hub, NHRP Peers: 10
Tunnel1, Type:Hub, NHRP Peers: 10 

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🛠️ Best Practices

• Use different ISPs for hubs 🌍
• Set clear routing metrics
• Monitor traffic regularly
• Test failover scenarios

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💡 Key Takeaways

• Dual DMVPN improves reliability
• Modern IOS simplifies configuration
• Math helps control routing behavior
• Failover becomes seamless

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🎯 Final Thought

Dual Hub Dual DMVPN isn’t just redundancy—it’s intelligent networking.

And with modern IOS, it’s finally practical to deploy at scale.

Setting Up Dual Hub DMVPNs: Redundancy Made Easy with Modern Cisco IOS

Dual Hub DMVPN: Complete Configuration & Optimization Guide

📚 Table of Contents

• Introduction
• Why Dual Hub DMVPN
• Deployment Models
• Single DMVPN
• Dual DMVPN
• Routing Protocols
• IOS Enhancements
• CLI Examples
• Key Takeaways
• Related Articles

📖 Introduction

Dynamic Multipoint Virtual Private Network (DMVPN) is a scalable VPN solution that allows secure communication over public networks. When combined with a dual hub architecture, it provides high availability and redundancy.

💡 Core Concept: DMVPN uses GRE + IPsec + NHRP to dynamically build tunnels.

🚀 Why Dual Hub DMVPN?

• High Availability
• Fault Tolerance
• Load Sharing
• Reduced Downtime

🔽 Expand: Real-world Scenario

If Hub1 fails, spokes automatically reroute traffic to Hub2, ensuring uninterrupted service.

🧩 Deployment Models

1. Single DMVPN Cloud

• One tunnel interface
• Two hubs (dual NHS)
• Simple design

2. Dual DMVPN Cloud

• Two tunnel interfaces
• Separate routing domains
• Advanced traffic control

📡 Single DMVPN Configuration

In this model, all routers belong to the same DMVPN cloud.

Configuration Code

interface Tunnel0
 ip address 192.168.1.2 255.255.255.0
 tunnel source GigabitEthernet0/0
 tunnel mode gre multipoint
 tunnel key 100
 tunnel protection ipsec profile IPSEC_PROFILE
 ip nhrp map 192.168.1.1 HUB1_PUBLIC_IP
 ip nhrp map 192.168.1.3 HUB2_PUBLIC_IP
 ip nhrp network-id 1
 ip nhrp nhs 192.168.1.1
 ip nhrp nhs 192.168.1.3

🔽 Expand Explanation

NHRP maps logical tunnel IPs to physical IPs. Dual NHS ensures redundancy.

🔁 Dual DMVPN Configuration

Each spoke connects to two hubs using separate tunnels.

interface Tunnel0
 ip address 192.168.1.2 255.255.255.0
 tunnel source GigabitEthernet0/0
 tunnel key 100
 ip nhrp nhs 192.168.1.1

interface Tunnel1
 ip address 192.168.2.2 255.255.255.0
 tunnel source GigabitEthernet0/1
 tunnel key 200
 ip nhrp nhs 192.168.2.1

🔽 Expand Benefits

Provides granular control and allows traffic engineering using routing metrics.

📊 Routing Protocols

EIGRP

• Easy metric manipulation
• Fast convergence

OSPF

• More complex
• Requires tuning

🔽 Expand Deep Comparison

EIGRP allows delay/bandwidth tuning, while OSPF uses cost-based routing requiring more manual adjustments.

⚙️ Cisco IOS 15.9 Enhancements

• Improved NHRP convergence
• DMVPN Phase 3 optimization
• Enhanced IPsec encryption
• Advanced logging tools

💡 Insight: Phase 3 enables direct spoke-to-spoke communication.

💻 CLI Output Examples

Show DMVPN Status

show dmvpn

Legend: Attrb --> S - Static, D - Dynamic
Tunnel0, NHRP Details
Type:Spoke, NHRP Peers:2
Peer NBMA Addr: 10.1.1.1
Peer NBMA Addr: 10.1.1.2

Debug Output

*Mar 1 12:00:01: NHRP: Resolution request sent
*Mar 1 12:00:02: NHRP: Resolution reply received

🔽 Expand CLI Explanation

Shows tunnel peers and NHRP resolution process.

🎯 Key Takeaways

• Dual Hub DMVPN ensures redundancy
• Single cloud = simple, less control
• Dual cloud = complex, more control
• EIGRP preferred for flexibility
• IOS 15.9 improves performance significantly

📘 Conclusion

Dual hub DMVPN designs provide scalable, resilient, and efficient networking solutions. Choosing between single and dual DMVPN depends on complexity vs control requirements.