Case Study: Simulating a Modern Enterprise Network

To demonstrate the principles of modern network engineering, I designed and simulated a complete multi-site enterprise network from the ground up. The objective was to build a realistic, production-grade infrastructure that incorporates the key pillars of a modern business network: high availability, robust security, and essential operational services. This case study documents the architecture and the real-world features I implemented.

Figure 1: The complete, high-availability network engineering. (Click to enlarge)

1. Core Resiliency: High Availability with HSRP

A modern network must guarantee uptime. The foundation of this design is a redundant core at the headquarters, built using the Hot Standby Router Protocol (HSRP). By deploying a pair of core switches in an Active/Standby configuration, I created a virtual gateway that ensures seamless, automatic failover. This architecture eliminates the risk of a single hardware failure causing a network-wide outage.

Primary Switch (Active). (Click to enlarge)

Secondary Switch (Standby). (Click to enlarge)

2. Operational Efficiency: Centralized DHCP Services

To ensure scalability and ease of management at the remote stores, I configured the local routers to function as DHCP servers. I designed separate, segmented IP pools for corporate data, guest access, and VoIP devices. This automates IP allocation, simplifies device onboarding, and enforces proper network segmentation from the moment a device connects.

DHCP pool configuration for VLANs at Store 2. (Click to enlarge)

3. Business Services: Enterprise VoIP Telephony

A key feature of any modern company is unified communications. I implemented an enterprise VoIP system using Cisco Unified CME (Communications Manager Express) on the store routers. This included configuring the core telephony service, creating a logical dial-plan with `ephone-dn`, and registering physical IP phones, enabling seamless calling between remote sites.

Cisco CME `telephony-service` and `ephone-dn` configuration. (Click to enlarge)

IP Phone initiating call (ringing out). (Click to enlarge)

IP Phone showing active connection. (Click to enlarge)

4. The Security Posture: Encryption and Segmentation

Security was architected into the network from the start. All traffic between the headquarters and remote stores is encrypted end-to-end using site-to-site IPsec VPNs. Furthermore, a critical zero-trust principle was enforced by using Access Control Lists (ACLs) to completely isolate the Guest WiFi network, strictly blocking it from accessing any internal corporate resources.

IPsec VPN Crypto Map. (Click to enlarge)

Guest Isolation ACL. (Click to enlarge)

Conclusion: Validation Through Stress-Testing

The success of the architecture was validated with a "pull-the-plug" stress test, simulating a total failure of the primary core switch. The video below demonstrates the network's ability to automatically detect the failure and reconverge in seconds, proving the design's resilience and ensuring business continuity.