Saturday, May 16, 2026

CCDE Enterprise WAN Redesign Case Study | MPLS vs DMVPN vs Internet WAN Architecture

CCDE Enterprise WAN Redesign Case Study – MPLS vs Internet vs DMVPN Architecture

CCDE Enterprise WAN Redesign Case Study – MPLS, Internet, DMVPN and Cloud Migration Architecture

Modern enterprise networking is no longer just about connecting routers and switches together. Today, enterprise architects must design scalable, cloud-ready, secure, automated, and cost-efficient infrastructures capable of supporting business growth, mergers, acquisitions, cloud migrations, real-time collaboration, and modern applications.

In this complete CCDE-style case study, we analyze the Fishers Healthcare System (FHS) enterprise network redesign project. This is a large healthcare organization with multiple hospitals, data centers, cloud integrations, MPLS WANs, IPsec deployments, and legacy routing environments.

🎯 What You Will Learn

  • Enterprise WAN redesign strategies
  • MPLS vs Internet WAN architecture
  • DMVPN scalability and design logic
  • EIGRP routing design analysis
  • Cloud migration considerations
  • Data Center Interconnect design
  • Voice CAC and QoS challenges
  • VPN scalability comparison
  • SDN and automation migration
  • CCDE-level decision making methodology
  • Business-driven architecture analysis
  • Routing protocol selection reasoning

Table of Contents

1. Understanding the Business Background

Fishers Healthcare System is one of the largest healthcare organizations in Indiana and among the largest healthcare companies in the United States.

After acquiring AHS, the company inherited:

  • 77 hospitals
  • 240 urgent care centers
  • Multiple physical therapy centers
  • Hospice businesses
  • Complex WAN environments
  • Multiple data centers
  • Different operational teams
  • Different WAN providers

This immediately created architectural complexity.

Enterprise Complexity Formula

$$ Complexity = Sites + Applications + WANs + Protocols + Teams $$

As acquisitions increase:

$$ Complexity \propto Acquisitions $$

This is one of the most important realities in enterprise architecture: business growth almost always increases technical complexity.

2. Existing Network Problems

The organization already identified several major problems:

  • Expensive MPLS circuits
  • Cloud migration challenges
  • Voice traffic failures
  • DCI congestion
  • Operational complexity
  • Poor scalability
  • Lack of automation
  • QoS inconsistencies
  • Legacy applications

💡 Important Design Observation

The organization is not simply replacing routers. This is a complete transformation project involving:

  • Business transformation
  • Cloud transformation
  • WAN redesign
  • Operational redesign
  • Data center modernization
  • Automation adoption

3. Business and Technical Requirements

CCDE candidates must always separate:

  • Business requirements
  • Technical requirements
  • Operational requirements

Business Requirements

  • Reduce WAN cost
  • Improve scalability
  • Support cloud migration
  • Support acquisitions
  • Reduce operational complexity

Technical Requirements

  • Secure transport
  • Support voice traffic
  • QoS support
  • Dynamic routing
  • Automation capabilities
  • Asymmetric traffic handling

Operational Requirements

  • Easy troubleshooting
  • Simple deployment
  • Scalable VPN model
  • Minimal manual intervention

Enterprise Design Equation

$$ Optimal\\ Design = Business\\ Goals + Technical\\ Requirements + Operational\\ Simplicity $$

4. Current Routing Architecture

The current routing protocol is EIGRP.

The organization uses:

  • Single EIGRP AS
  • One large network statement
  • BGP only at internet edge
  • Redistribution between BGP and EIGRP

Why This Becomes a Problem

As enterprise networks grow:

  • Large routing domains become unstable
  • Convergence becomes slower
  • Troubleshooting becomes difficult
  • Route leaks become more dangerous

EIGRP Query Scope Formula

$$ Query\\ Scope \propto Number\\ of\\ Routers $$

As the routing domain increases:

$$ Convergence\\ Time \uparrow $$

5. MPLS WAN Analysis

Traditional MPLS WANs provide:

  • QoS support
  • Predictable latency
  • Traffic engineering
  • Reliable SLAs

However modern enterprises face major MPLS challenges:

  • High cost
  • Slow bandwidth upgrades
  • Limited flexibility
  • Vendor dependency

MPLS Cost Model

$$ Cost_{MPLS} = Bandwidth \times SLA \times Distance $$

As bandwidth increases:

$$ Cost \uparrow\uparrow $$

6. Internet-Based WAN Analysis

Internet-based WAN designs offer:

  • Lower cost
  • High bandwidth availability
  • Faster deployment
  • Transport diversity

But internet WANs require:

  • Overlay VPNs
  • Encryption
  • Traffic engineering
  • Dynamic path selection

Internet WAN Equation

$$ Flexibility \propto Number\\ of\\ Available\\ Paths $$

But:

$$ Security = Encryption + Authentication $$

7. Voice CAC and QoS Issues

One of the biggest issues in this environment involves voice traffic.

Calls from AHS locations fail across DCI due to CAC restrictions.

This causes:

  • PSTN failover
  • Unexpected carrier bills
  • Poor user experience
  • Suboptimal routing

Voice Quality Formula

$$ MOS \propto \frac{1}{Latency + Jitter + Packet\\ Loss} $$

As DCI congestion increases:

$$ Voice\\ Quality \downarrow $$

8. Cloud Migration Architecture

The company plans to migrate applications to the cloud.

However:

  • Some applications are legacy
  • Some applications remain on-premises
  • Backend integrations are required
  • Containers are being introduced

Key Cloud Migration Challenges

  • Latency
  • Application dependencies
  • Security compliance
  • Traffic engineering
  • Data synchronization

Cloud Migration Dependency Formula

$$ Migration\\ Complexity = Legacy\\ Dependencies + Application\\ Coupling $$

9. DCI and Data Center Design

FHS currently uses:

  • Cisco Nexus 7000
  • Cisco Nexus 5000
  • Cisco Nexus 2000
  • OTV

OTV allows:

  • Layer 2 extension
  • VLAN stretching
  • Data center mobility

But Problems Exist

  • Large failure domains
  • Broadcast extension
  • Complexity
  • Troubleshooting challenges

Layer 2 Extension Risk

$$ Failure\\ Domain \propto VLAN\\ Stretching $$

10. SDN Fabric Migration

FHS wants to adopt SDN fabrics.

This aligns with modern data center trends:

  • Automation
  • Policy-driven networking
  • Application-centric design
  • Container integration

🎯 Critical CCDE Observation

The company initially wants a network-centric deployment. This is important.

Architects must understand:

  • Organizations rarely jump directly into fully automated SDN
  • Migration phases matter
  • Operational readiness matters
  • Human factors matter

11. Question 1 – Best WAN Topology

The best topology should:

  • Avoid DCI transit traffic
  • Support direct site communication
  • Enable cloud integration
  • Reduce WAN cost
  • Support scalable VPNs

CCDE candidates must avoid focusing only on technology.

The correct design must satisfy:

  • Business requirements
  • Operational requirements
  • Scalability requirements
  • Future migration plans

Topology Decision Formula

$$ Best\\ Design = Scalability + Simplicity + Flexibility + Cost\\ Efficiency $$

12. MPLS + Internet Design Discussion

Question 2 discusses combining MPLS and Internet.

Valid Reasons

  • Allows DIA
  • Provides diversity
  • Supports internet breakout
  • Reduces MPLS dependence

This is a hybrid WAN architecture.

Hybrid WAN Formula

$$ Hybrid\\ WAN = MPLS + Internet + Intelligent\\ Routing $$

13. Routing Protocol Selection

Possible protocols:

  • EIGRP
  • IS-IS
  • OSPF
  • MP-iBGP

Why EIGRP Remains Strong

  • Operational familiarity
  • Fast convergence
  • Summarization flexibility
  • Low operational disruption

Convergence Formula

$$ Convergence = Detection + Calculation + Installation $$

EIGRP optimizes:

$$ Calculation\\ Time $$

14. EIGRP Design Advantages

Valid Answers

  • Supports summarization anywhere
  • Provides fast failover
  • Supports scalability

Code Example

router eigrp 100
 network 10.0.0.0
 eigrp stub

router eigrp 100
 network 10.0.0.0
 no auto-summary
 eigrp stub connected summary
Detailed Explanation

EIGRP stub reduces query scope.

This improves:

  • Convergence
  • Scalability
  • CPU utilization

15. VPN Technology Comparison

VPN Type Scalable Multipoint Encryption Routing Support
GRE No No No Yes
L2L IPsec Low No Yes Limited
GETVPN Very High Yes Yes Yes
DMVPN High Yes Yes Yes
S-VTI Medium No Yes Yes

VPN Scalability Formula

$$ Tunnel\\ Count = \frac{N(N-1)}{2} $$

For full mesh:

$$ Scalability\\ Problem \uparrow $$

16. Best VPN Selection

DMVPN best meets the requirements.

Why?

  • Dynamic tunnels
  • Multipoint support
  • Routing protocol support
  • Scalability
  • Cloud readiness
  • Transport independence

DMVPN Dynamic Tunnel Formula

$$ Dynamic\\ Tunnel = NHRP + mGRE + IPsec $$

17. Why DMVPN Wins

Valid Reasons

  • Handles dynamic IP addressing
  • Provides encryption and scale
  • Supports large deployments

Code Example

interface Tunnel0
 ip address 10.1.1.1 255.255.255.0
 tunnel mode gre multipoint

interface Tunnel0
 ip address 10.1.1.1 255.255.255.0
 tunnel source GigabitEthernet0/0
 tunnel mode gre multipoint
 ip nhrp network-id 1
 ip nhrp authentication CISCO
 tunnel protection ipsec profile DMVPN-PROFILE
CLI Verification Output 
R1#show dmvpn

Legend: Attrb --> S - Static, D - Dynamic

Interface: Tunnel0
Type:Hub, NHRP Peers:2

Peer NBMA Addr Peer Tunnel Add State
10.1.1.2 172.16.1.2 UP
10.1.1.3 172.16.1.3 UP

DMVPN Scale Formula

$$ Scalability_{DMVPN} \propto Dynamic\\ Tunnel\\ Creation $$

18. WAN Design Mathematics

Bandwidth Utilization

$$ Utilization = \frac{Traffic}{Available\\ Bandwidth} \times 100 $$

Packet Loss Impact

$$ TCP\\ Throughput \propto \frac{1}{\sqrt{Packet\\ Loss}} $$

Latency Calculation

$$ Latency = Propagation + Serialization + Queuing $$

QoS Queue Formula

$$ Delay \propto Queue\\ Depth $$

19. CLI Design Examples

QoS Policy Example

policy-map VOICE
 class VOICE
  priority percent 30

class-map match-any VOICE
 match ip dscp ef

policy-map WAN-QOS
 class VOICE
  priority percent 30

 class class-default
  fair-queue
QoS Verification 
show policy-map interface tunnel0

20. Automation Strategy

FHS wants heavy automation adoption.

Future Technologies

  • Ansible
  • Python
  • REST APIs
  • SDN Controllers
  • Container orchestration

Automation Benefit Formula

$$ Operational\\ Cost \propto \frac{1}{Automation} $$

21. Key Design Takeaways

💡 Critical CCDE Lessons

  • Business requirements always drive architecture
  • Cloud migration changes WAN design
  • Operational simplicity matters
  • Scalability is critical
  • Voice traffic requires careful QoS planning
  • Hybrid WANs improve flexibility
  • DMVPN provides strong scalability
  • Automation is no longer optional
  • Routing protocol familiarity matters operationally
  • Migration planning is as important as final design

Final Conclusion

This enterprise healthcare redesign scenario demonstrates exactly why CCDE-level thinking is different from traditional certification approaches.

The correct architecture is not selected based only on:

  • Protocol popularity
  • Configuration simplicity
  • Vendor recommendations

Instead, the architect must analyze:

  • Business requirements
  • Operational readiness
  • Scalability
  • Cloud transformation goals
  • Voice application requirements
  • Cost optimization
  • Automation maturity
  • Migration complexity

The final recommendation leans toward internet-based WAN transport combined with scalable VPN technologies such as DMVPN while preserving operational familiarity with EIGRP during transition phases.

This approach balances:

  • Scalability
  • Security
  • Cost
  • Cloud readiness
  • Operational simplicity

This is exactly the kind of multidimensional analysis expected from modern enterprise architects and CCDE candidates.

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