Hierarchical Network Design

Hierarchical Network Design

To meet a customer's business and technical goals for a corporate network design, you might need to recommend a network topology consisting of many interrelated components. This task is made easier if you can "divide and conquer" the job and develop the design in layers. Network design experts have developed the hierarchical network design model to help you develop a topology in discrete layers. A hierarchical network design model breaks the complex problem of network design into smaller, more manageable problems. Each level, or tier in the hierarchy addresses a different set of problems. This helps the designer optimize network hardware and software to perform specific roles. For example, devices at the lowest tier are optimized to accept traffic into a network and pass that traffic to the higher layers. Cisco offers a three-tiered hierarchy as the preferred approach to network design.

In the three-layer network design model, network devices and links are grouped according to three layers: 

• Core
• Distribution
• Access

CORE LAYER

Core Layer consists of biggest, fastest, and most expensive routers with the highest model numbers and Core Layer is considered as the back bone of networks. Core Layer routers are used to merge geographically separated networks. The core layer provides an optimized and reliable transport structure by forwarding traffic at very high speeds. In other words, the core layer switches packets as fast as possible. Devices at the core layer should not be burdened with any processes that stand in the way of switching packets at top speed. This includes the following:

• Access-list checking
• Data encryption
• Address translation
• Layer 3 support
• Very high forwarding rates
• Gigabyte Ethernet/ 10 Gigabyte Ethernet
• Redundant components
• Link Aggregation
• Quality of Service (QoS)

DISTRIBUTION LAYER

The distribution layer aggregates the access traffic to the core layer, which is a the high speed backbone of the network.  So this allows for traffic to be classified into three different types of services in relation to the end users.  Distribution Layer is located between the access and core layers. The purpose of this layer is to provide boundary definition by implementing access lists and other filters. Therefore the Distribution Layer defines policy for the network. Distribution Layer include high-end layer 3 switches. Distribution Layer ensures that packets are properly routed between subnets and VLANs in your enterprise. Switch features in the Distribution layer. The distribution layer aggregates the data received from the access layer switches before it is transmitted to the core layer for routing to its final destination.

• Layer 3 support
• High forwarding rate
• Gigabyte Ethernet/ 10 Gigabyte Ethernet
• Redundant components
• Security policies/Access Control Lists
• Link Aggregation
• Quality of Service (QoS)

ACCESS LAYER

In a LAN environment, the access layer highlighted grants end devices access to the network. In the WAN environment, it may provide teleworkers or remote sites access to the corporate network across WAN connections. Access layer includes access switches which are connected to the end devices (Computers, Printers, Servers etc). Access layer switches ensures that packets are delivered to the end devices. Switch features in the access layer: The access layer supplies traffic to the network and performs network entry control. End users access network resources by way of the access layer. Acting as the front door to a network, the access layer employs access lists designed to prevent unauthorized users from gaining entry. 

• Port security
• VLANs
• Fast Ethernet/Gigabyte Ethernet
• Power over Ethernet (PoE)
• Link aggregation
• Quality of Service (QoS)

The benefit of dividing a flat network into smaller, more manageable blocks is that local traffic remains local. Only traffic that is destined for other networks is moved to a higher layer.

Layer 2 devices in a flat network provide little opportunity to control broadcasts or to filter undesirable traffic. As more devices and applications are added to a flat network, response times degrade until the network becomes unusable.

BENEFITS OF HIERARCHICAL NETWORK DESIGN

The main benefits of Cisco Three-Layer hierarchical model is that it helps to design, deploy and maintain a Scalable, trustworthy, cost effective hierarchical inter-network.

Better Performance: Cisco Three Layer Network Model allows in creating high performance networks

Better management & troubleshooting: Cisco Three Layer Network Model allows better network management and isolate causes of network trouble.

Better Filter/Policy creation and application: Cisco Three Layer Network Model allows better filter/policy creation application.

Better Scalability: Cisco Three Layer Network Model allows us to efficiently accommodate future growth.

Better Redundancy: Cisco Three Layer Network Model provides better redundancy. Multiple links across multiple devices provides better redundancy. If one switch is down, we have another alternate path to reach the destination.

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