Internetworking Part 10

Cisco Three-Layer Hierarchical Model

This is the last part of the Internetworking series and we will move on to another area of Cisco CCENT/CCNA Certification.

We have been exposed to hierarchies all throughout our lives.  Hierarchies work within the human race as well as the electronic and computer fields…this is just how everything seems to work, meaning through a set and organized fashion.  Well, not so much with the human race, but you get the idea.

There are three layers to the Cisco Hierarchical Model, which essentially equates to a pyramid:

  • The core layer: backbone
  • The distribution layer: routing
  • The access layer: switching

Each layer has specific duties and responsibilities.

  1. The Core Layer, or the backbone, is truly the core of the network itself because it is responsible for the transporting of large amounts of traffic and must do it both reliably and quickly.  If there is a failure at the core, then potentially every user may be affected.  So, latency and and speed are a big concern to keep in mind.
  2. The Distribution Layer also referred to as the workgroup which provides routing.  This is the layer where all user data is processed which forwards requests if necessary.  The main function is to provide routing, filtering, WAN access and to determine how packets will access the core, if necessary.
  3. The Access Layer and is sometimes referred to as the desktop layer.  The network resources most users need will be available local to this layer.  Some functions are as follows:
  • Use of access control and policies, which are a continuation from the distribution layer
  • Segmentation or the creation of separate collision domains
  • Workgroup connectivity via the distribution layer

Though, I have not seen any reference to this 3 layer hierarchical model, as it is more than likely Cisco proprietary – because it is a Cisco test, it is testable.  But my personal & non-professional, opinion is that you will not see much of this outside of an all Cisco system.

See also: Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8, Part 9

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.


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