Three Tier Architecture Cisco

As companies grow, theirs networks become more complex.

Without a well-defined network design, performance suffers, troubleshooting becomes a nightmare for network engineers and scalability is impossible.

To address all these challenges, large enterprises can use the Three Tier Architecture Cisco model, which was originally developed by Cisco to organize networks more efficiently.

Figure 1 – Three Tier Architecture: Core, Distribution, and Access layers

As shown in the diagram above, this model organizes the network into three distinct layers:

This model is composed of three distinct layers:

• Core Layer

• Distribution Layer

• Access Layer

Each layer has a specific role and you need to understand every layer for your CCNA Exam.

Understanding the Three Tier Architecture Cisco model requires examining each layer individually, let's dive into the Access Layer.

Let's start with the Access Layer, the layer closest to your users.

Figure 2 – The Access Layer connects end-user devices

The Access Layer mainly operates at Layer 2 of the OSI model (Switching). At this level, devices forward frames based on MAC addresses, not IP addresses.

The Access Layer is responsible for connecting end devices such as:

• PCs

• IP phones

• Printers

• Wi-Fi Access Point (AP)

This layer is the link between users and the network.

Essential functions used at this layer are:

• Physical network access links for endpoints and wireless access points (APs).

• Power over Ethernet (PoE) to power devices such as IP telephones or wireless APs.

• VLANs to segment the network and create smaller broadcast domains.

• Spanning Tree Protocol (STP/RSTP) to prevent loops and ensure a resilient network.

  Security mechanisms:

  • Port security to restrict access based on MAC addresses.

  • DHCP Snooping to prevent rogue DHCP servers.

  • Dynamic ARP Inspection (DAI) to protect against ARP spoofing attacks.

• Quality of Service (QoS) trust boundary established by applying QoS classification and marking at the edge of the network.

So it's through the Access Layer that the user interacts with the network infrastructure.

Let's move on to the Distribution Layer.