Why Core or Backbone is used in Networking?

Why Core or Backbone is used in Networking?. Before we start explaining this question, let's note that these two terms are used interchangeably. Usually, Service Providers use Backbone, and Enterprise Networks use Core terminology but they are the same thing.


Why Network Core is Necessary?

The Key Characteristics of the Core, the Backbone part of the networks are:

  • High-Speed Connectivity. Today it is 100s of Gigabit networks and is usually used as a bundle to increase the capacity.
  • Bringing Internet Gateway, Access, Aggregation, and Datacenter networks together. It connects many different parts of the network, and glues together.
  • Redundancy and High Availability are so important. Redundant physical circuits and devices are very common.
  • Failure impact is so high in this module, compared to other modules
  • Full Mesh or Partial Mesh deployment is seen mostly as these type of topologies provides the most amount of redundancy and the direct path between the different locations.
  • Commonly known in the Operator community as Backbone or ‘P Layer

Redundancy in this module is very important.

Most of the Core Network deployments in ISP networks are based on Full Mesh or Partial Mesh.

The reason for having full mesh physical connectivity in the Core network is that full mesh connectivity provides the most optimal network traffic and the shortest path between the two locations.

But not every network can have full mesh architecture, because it is the most expensive design option.

Instead, many operators connect their Core/Backbone locations in a partial mesh model.

In the partial mesh physical connectivity model, all of the core locations are not connected to each other, instead only the Core POP locations which have high network traffic demand are connected together.

Core/Backbone provides scalability to the Service Provider networks.

Without this layer, many Aggregation layers are required to be connected to each other to provide end-to-end connectivity.

This would be too costly and so many physical links are required to be provisioned.

The Core layer reduces the number of circuit requirements between different Aggregation networks.


If the cost is a concern and size is small and scalability is not critical consideration, then the network can be designed by collapsing Aggregation and Core networks and having only one layer.  

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Orhan Ergun, CCIE/CCDE Trainer, Author of Many Networking Books, Network Design Advisor, and Cisco Champion 2019/2020/2021

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