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CCNP/CCIE ENCOR Exam Series: Hierarchical LAN Design



This article discusses topics covered in Chapter 22 of the CCNP & CCIE ENCOR OCG.


Exam Topic 1.1: Enterprise network design such as Tier 2, Tier 3 & Fabric Capacity Planning

Key Points about Hierarchical LAN Design

The Hierarchical Model divides your network into 3 modular layers Access, Distribution, and Core. Each layer serves a specific function and these layers can be easily replicated throughout your network.

  • Access Layer: Gives endpoints and users access to the network via wired and wireless technologies

  • Distribution Layer: Provides an aggregation point for the access layer as well as a boundary between the access and core layer.

  • Core Layer: Provides connectivity to the distribution layers in large environments and home to the core network services (Data Center, Internet etc)

What are the Benefits?

This model offers the following benefits:

  • Easily scalable

  • Simplified Management and Troubleshooting

  • Provides fault containment

  • Minimized effect of changes

Access Layer

Gives endpoints and users access to the network via wired and wireless technologies

  • Commonly referred to as the Network Edge

  • Provides high bandwidth connectivity using wired and wireless technologies

  • QoS is typically in place here to enhance the QoE

  • Segmented with VLANs

  • Plays a major role in the security of the network

Distribution Layer

Aggregation Point for the access layer provides a service and control boundary between the core and access layers

  • Aggregates the Access layer switches

  • Provides a boundary between the L2 Domain and the L3 domain of the core

  • Prevents the propagation of L2 faults -> STP, Loops

  • Provides a point of route summarization for IP info as it enters the core

  • Easier troubleshooting

  • Reduction in protocol overhead

  • Switches at the layer should be deployed in pairs for redundancy and fully connected to the access switches with L2 or L3 Links

Core Layer

The backbone and aggregation for multiple networks

  • Provides scalability, HA, and Fast Convergence

  • Provides interconnectivity between the access layer and the data center, public & private clouds, WAN and other network services

  • Reduces network complexity

  • Should be considered once a network grows to 3 distribution layers.

Design Options

There are 6 different approaches to the Design Model:

  • Three-Tier

  • Two-Tier (Collapsed Core)

  • Layer 2, STP Based

  • Layer 3, Routed Access

  • Simplified Campus Design

  • Software-Defined Access

We'll dive more into these Design Options in my next article.

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