A campus network is generally the portion of the enterprise network infrastructure that provides access to network communication services and resources to end users and devices that are spread over a single geographic location. It may be a single building or a group of buildings spread over an extended geographic area. Normally, the enterprise that owns the campus network usually owns the physical wires deployed in the campus. Therefore, network designers typically tend to design the campus portion of the enterprise network to be optimized for the fastest functional architecture that runs on high-speed physical infrastructure (1/10/40/100 Gbps). Moreover, enterprises can also have more than one campus block within the same geographic location, depending on the number of users within the location, business goals, and business nature. When possible, the design of modern converged enterprise campus networks should leverage the following common set of engineering and architectural principles 10:
- Hierarchy
- Modularity
- Resiliency
Enterprise Campus: Hierarchical Design Models
The hierarchical network design model breaks the complex flat network into multiple smaller and more manageable networks. Each level or tier in the hierarchy is focused on a specific set of roles. This design approach offers network designers a high degree of flexibility to optimize and select the right network hardware, software, and features to perform specific roles for the different network layers.
A typical hierarchical enterprise campus network design includes the following three layers:
- Core layer: Provides optimal transport between sites and high-performance routing. Due the criticality of the core layer, the design principles of the core should provide an appropriate level of resilience that offers the ability to recover quickly and smoothly after any network failure event with the core block.
- Distribution layer: Provides policy-based connectivity and boundary control between the access and core layers.
- Access layer: Provides workgroup/user access to the network.
The two primary and common hierarchical design architectures of enterprise campus networks are the three-tier and two-tier layers models.
Three-Tier Model
This design model, illustrated in Figure 3-1, is typically used in large enterprise campus networks, which are constructed of multiple functional distribution layer blocks.
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Figure 3-1 Three-Tier Network Design Model
Two-Tier Model
This design model, illustrated in Figure 3-2, is more suitable for small to medium-size campus networks (ideally not more than three functional disruption blocks to be interconnected), where the core and distribution functions can be combined into one layer, also known as collapsed core-distribution architecture.
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Figure 3-2 Two-Tier Network Design Model