Enterprise Campus Network Design

Networks can be designed in layers using a set of building blocks that can organize and streamline even a large, complex campus network. These building blocks can then be placed using several campus design models to provide maximum efficiency, functionality, and scalability.
There are two ways to design Enterprise Network i.e

1. Hierarchical Network Design
2. Modular Network Design

Hierarchical Network Design

A campus network is an enterprise network consisting of many LANs in one or more buildings, all connected and all usually in the same geographic area. A company typically owns the entire campus network and the physical wiring. Campus networks commonly consist of wired Ethernet LANs and shared wireless LANs.

An understanding of traffic flow is a vital part of the campus network design. You might be able to leverage high-speed LAN technologies and “throw bandwidth” at a network to improve traffic movement. However, the emphasis should be on providing an overall design that is tuned to known, studied, or predicted traffic flows. The network traffic can then be effectively moved and managed, and you can scale the campus network to support future needs.

A hierarchical network design involves dividing the network into discrete layers. Each layer, or tier, in the hierarchy provides specific functions that define its role within the overall network. Traffic flows in a enterprise networks can be classified as three types: core, distribution, and access layer.
 Cisco_hierarchial_Model


Access Layer

The access layer exists where the end users are connected to the network. Access switches usually provide Layer 2 (VLAN) connectivity between users. Devices in this layer, sometimes called building access switches, should have the following capabilities:

■ Low cost per switch port
■ High port density
■ Scalable uplinks to higher layers
■ High availability
■ Ability to converge network services
■ Security features and quality of service

Distribution Layer

The distribution layer provides interconnection between the campus network’s access and core layers. Devices in this layer, sometimes called building distribution switches , should have the following capabilities:

■ Aggregation of multiple access layer switches
■ High Layer 3 routing throughput for packet handling
■ Security and policy-based connectivity functions
■ QoS features
■ Scalable and redundant high-speed links to the core and access layers

Core Layer

A campus network’s core layer provides connectivity between all distribution layer devices. The core, sometimes referred to as the backbone, must be capable of switching traffic as efficiently as possible. Core switches should have the following attributes:

■ Very high Layer 3 routing throughput
■ No costly or unnecessary packet manipulations
■ Redundancy and resilience for high availability
■ Advanced QoS functions

Devices in a campus network’s core layer or backbone should be optimized for high-p rformance switching. Because the core layer must handle large amounts of campus-wide data, the core layer should be designed with simplicity and efficiency in mind.



Modular Network Design

Designing a new network that has a hierarchy with three layers is fairly straightforward. You can also migrate an existing network into a hierarchical design. The resulting network is organized, efficient, and predictable. However, a simple hierarchical design does not address other best practices like redundancy, in the case where a switch or a link fails, or scalability, when large additions to the network need to be added.

Consider the hierarchical network shown in the left portion of Figure below. Each layer of the network is connected to the adjacent layer by single links. If a link fails, a significant portion of the network will become isolated. In addition, the access layer switches are aggregated into a single distribution layer switch. If that switch fails, all the users will become isolated.
Modular Network
To mitigate a potential distribution switch failure, you can add a second, redundant distribution switch. To mitigate a potential link failure, you can add redundant links from each access layer switch to each distribution switch. One weakness is still present in the redundant design i.e the core layer has only one switch. If that core switch fails, users in the access layer will still be able to communicate with each other. However, they will not be able to reach other areas of the network, such as a data center, the Internet, and so on. To mitigate the effects of a core switch failure, you can add a second, redundant core switch. Redundant links should also be added between each distribution layer switch and each core layer switch.

With so many interconnecting links between switches, it becomes a “brain-buster” exercise to figure out where VLANs are trunked, what the spanning-tree topologies look like, which links should have Layer 3 connectivity, and so on. Users might have connectivity through this network, but it might not be clear how they are actually working or what has gone wrong if they are not working. This network looks more like a spider’s web than an organized, streamlined design.
Modular Network

To maintain organization, simplicity, and predictability, you can design a campus network in a logical manner, using a modular approach. In this approach, each layer of the hierarchical network model can be broken into basic functional units. These units, or modules, can then be sized appropriately and connected, while allowing for future scalability and expansion.

You can divide enterprise campus networks into the following basic elements or building blocks:

■ Switch block: A group of access layer switches, together with their distribution switches. This is also called an access distribution block , named for the two switch layers that it contains. The dashed rectangle in Above Figures represent typical switch blocks.

■ Core: The campus network’s backbone, which connects all switch blocks.