Designing high-availability (HA) architectures is one thing. Watching them work under failure conditions is another entirely.
Theory becomes real only when you see the packets flow, fail, and recover.

In this lab, we’ll build a three-layer campus network model in Cisco Packet Tracer—designed for maximum availability. You’ll learn to simulate redundancy, implement key protocols, and observe how traffic remains uninterrupted even during link or device failure.

What is Cisco Packet Tracer?

Packet Tracer is a cross-platform visual simulation tool designed by Cisco Systems that allows users to create network topologies and mimic modern computer networks. The software allows users to simulate the configuration of Cisco routers and switches using a simulated command-line interface. Packet Tracer uses a drag-and-drop user interface, allowing users to add and remove simulated network devices as needed.

You can download the Packet Tracer from the following link: https://www.netacad.com/about-networking-academy/packet-tracer/

Objective: What You’ll Build

By the end of this lab, you’ll have a working redundant campus network that:

• Survives individual switch or link failures.
• Uses EtherChannel for link aggregation (redundant and load-balanced connections).
• Uses Rapid Spanning Tree Protocol (RSTP) for loop prevention and quick recovery.
• Uses HSRP (Hot Standby Router Protocol) for redundant gateways.

You’ll witness convergence, resilience, and stability in a real-time simulation.

Lab Overview

The lab depicted above represents a mature, enterprise-grade campus network built on high availability (HA) and modularity principles. The design demonstrates the classic separation of core, distribution, and access layers—ensuring that no single device or path failure can disrupt overall connectivity.

Core Concepts at a Glance

At the heart of the topology lies a robust core consisting of redundant switches and connections. This backbone enables high-speed, low-latency routing between all sections of the network. Notice that every key device—whether a distribution or multilayer switch—has dual or even triple connections ensuring failover. The green and black dashed lines denote active and backup links, guaranteeing seamless operation even during simulated outages.

Distribution & Access Layers

Each “pod” of the network, whether for server farms or large endpoint deployments, is tied to the distribution layer via highly available connections. The distribution switches act as intelligent intermediaries, managing VLAN routing, access policies, and redundancy (often leveraging HSRP or VRRP for gateway failover). From the distribution layer, multiple access switches fan out to connect dozens of endpoint devices across several VLANs.

Each access block is designed with load balancing and fault tolerance in mind. If one uplink or switch fails, traffic quickly reroutes, minimizing impact on users and critical servers.

Server and Edge Segments

To the right of the diagram, a specialized server segment is isolated yet protected through similar HA principles. Here, multilayer switches provide resilient connectivity to core and distribution, while also balancing load between servers and managing VLAN segmentation.

At the top of the diagram, routed test traffic simulates external connectivity, confirming that the HA architecture can support real-world use cases, including cloud connectivity and WAN uplinks

In the next section, I’ll be sharing screenshots and explanations of the main protocol configurations to give you a deeper technical understanding of how each role contributes to the overall resilience and high availability of the architecture.

The Core Layer

Within this layer, I used EIGRP as the routing protocol to maintain routes
between different network blocks. I linked the two Layer 3 switches using the Layer 3 EtherChannel mechanism to provide redundancy and high capacity between the cores.

The Edge Layer

In this layer, I defined the default route to the outside and implemented the NAT protocol to allow multiple devices on a local network to be mapped to a single public IP address to conserve IP addresses. They can therefore be routed to the outside network.

Distribution Layer

The distribution layer is used to allocate IP addresses to end hosts (DHCP) and act as a default gateway using HSRP. I also used RapidPVST+ to prevent layer 2 loops in the block. I set some VLANs by a distribution switch; the left switch handles VLANs 3 and 5, and the other for the rest.

The Access Layer

Within this layer, I configured trunking to distribute tagged VLANs within the network block and access ports to allow end hosts to communicate within the network. I’ve also configured port-security to restrict access to Switch’s ports.

Conclusion

This lab brought theory to life—transforming abstract concepts of network high availability into a working, observable reality. By structuring the campus network in modular layers, deploying redundant connections at every level, and leveraging protocols like EtherChannel, Rapid Spanning Tree (R-PVST+), and HSRP, we demonstrated not just resilience, but self-healing at the core of the topology.

Every simulated link failure, switch outage, or device misconfiguration was met, not with disruption, but with seamless recovery. The design proved its worth: with multiple paths, fast convergence protocols, and redundant gateways, user connectivity survived most scenarios with barely a hiccup.

More importantly, this lab illustrates a deeper truth: resilience isn’t achieved by accident—it’s engineered. It flows from thoughtful architecture, rigorous protocol integration, and relentless hands-on testing. Whether you’re building campus networks in the real world or architecting fault-tolerant solutions in the cloud, the underlying philosophy remains unchanged—design for failure, automate recovery, and document every step.

If you’ve followed along, you now have a solid foundation in both the logic and the practicalities of high-availability networking. In the next post, I’ll be sharing detailed configuration screenshots for each protocol, so you can visualize exactly how EtherChannel, RSTP, HSRP, and advanced VLANs operate within this architecture. Stay tuned and keep building—for every resilient network starts with a single, well-planned lab.