Top-down vs. Bottom-up Network Design

Designing a network presents several challenges, particularly when time is of the essence. Where you begin the design process at the bottom of the OSI model with the physical layer, or at the top with the application layer, is critical to your success. Let's explore each approach (bottom-up vs. top-down), including the pros and cons of each. Here, we examine these two approaches.

Bottom-up Approach: This approach begins with the physical layer of the OSI model and works its way up. New, higher bandwidth links might be purchased, as well as new routers, switches, firewalls, etc. Designing a network with a bottom-up approach enables you to get your network set up much faster.

Top-down Approach: With this approach, we are going to start with the requirements of the organization, the technology that is needed, and then design it from the top-down. The application layer is the starting point, and the applications and services that are desperately needed are analyzed for their specific requirements first.  

Here is a look at some important comparison points between these very different approaches: 

Choosing the design approach that best fits your needs will result in a stronger network. Recognizing the pros and cons of each approach can help you build the case for the appropriate choice, giving you the opportunity to build a network that will meet the needs of the project or organization — and improve network performance.

Learn more about network design with our new course: Cisco CCDA 200-310 DESGN.