hierarchical network Design

Cisco Borderless Networks enable secure, seamless connectivity for any user, device, or location, integrating wired and wireless access with advanced policy and performance management. Designed to address IT challenges like mobility, security, and scalability, this architecture leverages Cisco Catalyst switches, ISR routers, and tools like Cisco DNA Center. For CCNA and CCNP students, understanding Borderless Networks is crucial for mastering campus network design, a key exam topic. This article explores the hierarchical design, key components, and practical configurations to help you excel in Cisco certifications.

Cisco Borderless Networks Overview

Cisco Borderless Networks integrate wired and wireless access, delivering network and endpoint services through a scalable, secure architecture. Key services include:

• Network Services: Routing, QoS, and security policies via Cisco Catalyst switches (e.g., 9300 series) and ISR routers (e.g., 4400 series).
• Endpoint Services: Support for diverse devices (IP phones, laptops, IoT) using Cisco Identity Services Engine (ISE) for access control.
• Management: Cisco DNA Center provides centralized configuration, monitoring, and automation.

This design ensures seamless connectivity, high availability, and optimization, critical for CCNA/CCNP exam topics like network design and security.

Principles of Cisco Borderless Switched Networks

The Cisco Borderless switched network is built on four core principles, essential for CCNA and CCNP students to understand for designing scalable, secure campus networks:

• Hierarchical Network Design: Organizes the network into access, distribution, and core layers, each with specific roles. For example, Cisco Catalyst 9200 switches at the access layer connect end devices, while Catalyst 9500 switches at the core provide high-speed backbone connectivity.
• Modularity: Allows independent scaling of each layer, simplifying upgrades. Cisco DNA Center supports modular configurations, enabling easy addition of new switches or services.
• Resiliency: Ensures high availability using protocols like HSRP on Cisco routers and EtherChannel on switches to provide failover and redundancy, a key CCNP topic.
• Flexibility: Supports diverse devices and applications (e.g., VoIP, wireless) with Cisco ISE for access control and QoS for traffic prioritization, critical for unified communications.

These principles enable secure, scalable networks, aligning with CCNA/CCNP exam objectives on campus network design. It is very important to understand the principle to fit a different situation. The hierarchical borderless switched network provides a base for the network designer to cover security, mobility, and unified communication features. Cisco designs three-tier and two-tier hierarchical networks for a campus.

Hierarchical Network Design in Cisco Borderless Networks

Cisco’s hierarchical network design divides campus networks into access, distribution, and core layers, ensuring scalability and efficiency. Below are the layers, their roles, and Cisco-specific implementations.

Access, Distribution, and Core Layers

Access Layer

The access layer is where traffic enters or exits the campus network. It is also the edge of the campus network. Usually, the main function of an access layer is to give network connectivity and access to end-users.  The switches of the access layer connect to the switches of the distribution layer. The switches in the distribution layer apply network foundation technologies such as routing, QoS, and security.

To meet user needs and network applications, the next-generation switching platforms now present extra converged, integrated, and quick services to different types of endpoints at the edge of the network. Creating intelligence into the switches of an access layer allows applications to act more capably and securely on the network.

• Role: Connects end devices (PCs, IP phones, wireless APs) to the network, providing edge connectivity.
• Cisco Devices: Cisco Catalyst 9200 or 9300 switches for high-density ports and PoE support.
• Features: Implements VLANs (e.g., VLAN 10 for voice), QoS for traffic prioritization, and Cisco ISE for secure access.
• CCNA/CCNP Relevance: Configure VLANs and port security (switchport mode access, switchport port-security).

Distribution Layer

The distribution layer connects the access and core layers and includes many important functions. This layer provides intelligent switching and routing. It also provides network access policy functions to access the network and differentiated services to different classes of service applications at the edge of the network.

This layer also provides ease of use throughout the redundant distribution layer switches to the end-user and equal-cost paths to the core layer. The distribution layer also aggregates large-scale wiring closet networks, Layer 2 broadcast domains, and Layer 3 routing boundaries.

• Role: Aggregates access layer traffic, provides routing, QoS, and security policies.
• Cisco Devices: Cisco Catalyst 9300 or 9400 switches for redundancy and policy enforcement.
• Features: Supports HSRP for failover, ACLs for security, and inter-VLAN routing.
• CCNA/CCNP Relevance: Learn to configure HSRP (standby 1 ip 192.168.1.1) and QoS policies.

Core Layer

This layer is the backbone of the Cisco borderless network. The core layer connects several layers of the campus network, works as the aggregator for all the other campus blocks, and interconnects the campuses inside the network. The core layer’s main functions are speedy fault isolation and high-speed backbone connectivity.

• Role: Serves as the high-speed backbone, connecting distribution layers and campus blocks.
• Cisco Devices: Cisco Catalyst 9500 or Nexus 9000 switches for low-latency, high-throughput connectivity.
• Features: Uses OSPF or BGP for routing and EtherChannel for link redundancy.
• CCNA/CCNP Relevance: Understand core routing protocols and redundancy (ip routing, port-channel load-balance).

Collapsed Core Network

A three-tier campus network is usually planned for organizations where access, distribution, and core are required as separate layers. This is required because of the need for a basic, cost-effective, scalable, and efficient physical layout design for a large-scale network with many campuses. The best practice is to make an extended-star physical topology from the main campus to all other campuses.

A campus with fewer users accessing the network or a single-building campus usually does not require separate core and distribution layers. The network structure required in this situation is called a collapsed network.

It is also called a two-tier campus network.  In a collapsed network, the role of the core switches moves to the distribution switches, merging the core and distribution layers. The figure below illustrates the collapsed campus network example.

• Role: Combines core and distribution layers for smaller campuses or single-building networks, reducing costs.
• Cisco Devices: Cisco Catalyst 9300 switches handle both distribution and core functions.
• Design: Uses a two-tier (access and collapsed core) topology, ideal for small-to-medium networks with fewer users.
• CCNA/CCNP Relevance: Configure a collapsed core switch for routing and aggregation (ip routing, vlan 10,20,30).