Collapsed Core

1.6 Compare and contrast network topologies, architectures, and types

📘CompTIA Network+ (N10-009)

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A Collapsed Core is a network design architecture used in medium to large networks. It simplifies the traditional three-layer network model by combining layers, which can save cost and make management easier.

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1. Understanding the Traditional Three-Layer Network

Before understanding collapsed core, it’s important to know the three-layer network model:

1. Core Layer – The backbone of the network. It’s responsible for fast, reliable routing between different parts of the network. Usually very high-speed devices are used here.
2. Distribution Layer – Acts as a gateway between the core and access layers, handling routing, filtering, and network policies.
3. Access Layer – Where devices like computers, printers, and servers connect to the network.

A standard three-layer network is efficient but can be expensive and complex, especially for medium-sized organizations.

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2. What is a Collapsed Core?

A Collapsed Core is when the core layer and the distribution layer are combined into a single layer.

• Instead of having separate devices for core and distribution, a single set of high-performance switches handles both roles.
• This reduces the number of devices and simplifies network design.

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3. Key Characteristics of Collapsed Core

1. Simplified Design
   • Fewer devices in the network.
   • Easier to manage and maintain.
2. Cost-Effective
   • Combines layers, so fewer switches are needed.
   • Reduces hardware, power, and cooling costs.
3. High Performance
   • Collapsed core switches are usually high-capacity, fast switches, capable of handling all traffic efficiently.
4. Scalability
   • Can grow by adding additional high-performance switches.
   • Supports larger networks without adding extra layers.

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4. How It Works in a Network

Imagine a medium-sized organization:

• Instead of having a core switch connecting all the distribution switches, and multiple distribution switches connecting access switches, the organization uses two high-end switches that act as both core and distribution.
• Access switches then connect directly to these collapsed core switches.

This creates a network that looks simpler but still allows fast routing and connectivity.

Diagram (simplified):

Access Layer Switches
   |       |       |
-----------------------
|   Collapsed Core   |
| (Core + Distribution)
-----------------------

• Access switches → end devices (computers, printers, servers)
• Collapsed core → routing and forwarding for all access switches

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5. Advantages

1. Reduced Complexity – Fewer layers to configure.
2. Cost Savings – Less hardware needed.
3. High-Speed Backbone – Since the collapsed core handles both routing and distribution, data flows quickly.
4. Easier Troubleshooting – Fewer devices mean fewer points of failure.

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6. Disadvantages

1. Single Point of Failure – If the collapsed core switch fails, a lot of the network could go down.
   • Mitigation: Use redundant collapsed core switches.
2. Limited Scalability in Very Large Networks – For huge networks, the collapsed core might not handle all the traffic efficiently.

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7. Real-Life IT Environment Examples

• Corporate LAN – A medium-size office may use two high-capacity switches in a data center as a collapsed core. Access switches in different departments connect to these switches.
• Data Center Setup – Instead of separate distribution and core layers, a collapsed core switch handles all routing between servers and the access layer.
• Small ISP or Branch Office – They might implement a collapsed core to reduce hardware and simplify management while still having redundancy.

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8. Exam Tips

1. Know that Collapsed Core = Core + Distribution combined.
2. Understand advantages (cost, simplicity) and disadvantages (single point of failure).
3. Remember it is common in medium-to-large networks, but not always used in very large enterprise networks where traffic is massive.
4. For redundancy, always pair collapsed core switches.

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✅ In short:
A collapsed core simplifies a network by combining core and distribution layers into one set of high-performance switches. It reduces cost and complexity but needs redundancy to avoid a single point of failure. It’s popular in medium-to-large IT networks.

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