The data center, core, and user networks
First, let's see what the areas in the organization's data network are. The data center is the network that holds the majority of the organization's servers. In many cases, as shown in the following diagram, we have two data centers that work in high availability mode; that is, if one data center fails, the other one can fully or partially take its place.
The user networks depend on the size, geographical distribution, and the number of users in the organization. The core network is the backbone that connects the users to the data center, remote offices, and the internet. The distribution switches will be in central locations in the campus and the access switches are located in buildings and small areas.
The data center, core, and user networks are illustrated in the following diagram, which is of a typical mid-sized network:
Figure 1.2 – The data center, core, and user networks
At the top, we can see the data center switches, when every server is connected via two cables. This connectivity can be implemented as port redundancy for redundancy only or Link Aggregation (LAG) for redundancy and load sharing. A typical connection is implemented with two wires, copper or fiber, when heavy-duty servers on server blades can be connected with 2-4 wires or more.
In the center, we can see the core switches. As the name implies, they are the center of the network. They connect between the data center and the user network, and they connect to remote sites, the internet, and other networks. The connectivity between the core switches and the data center switches can be implemented in Layer 2 or Layer 3, with or without an overlay technology, as we will see later in this chapter.
The user network holds the distribution and access areas. The access layer holds the switches that connect to the users, while the distribution layer aggregates access switches. For example, in a campus network, there will be a distribution switch for every building or group of buildings, while the access switches are connected to the nearest one. Distribution switches are usually installed in a redundant topology – that is, two switches per site – when the access switches are connected to both.
In the next section, we will learn about Layer 2 and Layer 3 by examining the data flow and how data passes through the network. We will describe various design options and describe the pros and cons from a security point of view.