Cisco’s Three Layer Architecture Model
When Cisco talks about designing large networks, they like to break it down into different layers that display an ideal architecture. This is what any large network usually looks like in a nutshell:
These three layers describe what a campus WAN/LAN topology should look like. A campus LAN, usually is thought of a college network of some sort right? Well, it does, but “campus” can be an ambiguous term. A campus LAN really means its a network that is laid out on a company’s grounds, a group of buildings that would connect to one another, but they all lead to one single core part of the network. This could mean a university network, a hospital network, a federal agency network, a factory network, a network at a set of corporate buildings, etc. It’s simply the ideal network Cisco presents to you when talking about the architecture of large networks.
In this model shown above, you’ll see there is quite a bit of redundancy. All the core switches/routers will have more than one connection to the distribution switches, as the access switches will have multiple connections to the distribution switches. This redundancy is for obvious purposes: to reduces the chances of total network failure. When a link goes bad, the switches will always have an available path to the switch it was always once connected to. Of course, redundant links are there so the network doesn’t fail completely, but that does not mean its permanent. Once a link goes down, the device providing the alternate path will take an increase in data traffic, thus, making the part of the network it provides connectivity to, as well as the device that lost the connection, work harder and slow things down.
- Core Layer: As the name tells you, this is where every part of your network completely ties in, and usually this is where your Internet connections and other WAN connections come in. Also known as the backbone, this is where every point in your organization’s network will point to. This is usually where you’ll find your company’s corporate servers, your company’s cloud, where your network apps are, domain controllers (you will also see other servers and DCs scattered throughout a network, as well, and they are placed there for a good reason, such as providing end networks with services.)
- Distribution Layer: These are usually switches that act as the middle ground between your end user switches and the core of your network. These connect your organization’s core, to your end-user switches, and will pass data between them.
- Access Layer – This is where all your end users connect. The “access” point of how an end device will connect to a large network. Whether it be from a smartphone, a laptop, desktop, thin client, tablet, PDA, etc.
A neat site you can look to, where you can find lots of different topologies, is RateMyNetworkDiagram.com. Here you’ll find all sorts of topologies, from small home networks to large corporate networks. What we are looking for here though are large networks that use this type of architecture. See if you can find Cisco’s three-layered architecture implemented in these real network topologies.
Here are some examples: