🌐 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.
📚 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
🏗️ Architecture Explained
- Two hubs → Hub1 & Hub2
- Two DMVPN clouds
- Each spoke connects to both hubs
👉 Result: Redundancy + Load balancing + Better control
📐 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:
\[ Traffic \rightarrow Backup\ Hub \]
⚠️ 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 ...
🚀 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
⚙️ 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
🖥️ CLI Output
Show DMVPN Status
Router#show dmvpn Tunnel0, Type:Hub, NHRP Peers: 10 Tunnel1, Type:Hub, NHRP Peers: 10
🛠️ Best Practices
- Use different ISPs for hubs 🌍
- Set clear routing metrics
- Monitor traffic regularly
- Test failover scenarios
💡 Key Takeaways
- Dual DMVPN improves reliability
- Modern IOS simplifies configuration
- Math helps control routing behavior
- Failover becomes seamless
🎯 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.
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