Designing the Network Topology and Solutions CCIE Security Training in Gurgaon

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This section describes the top-down approach for network design, reviews pilot and prototype test networks, and describes the components of the design document. As part of the Design phase of the PPDIOO methodology, a top-down approach is used that begins with the organization's requirements before looking at technologies. Network designs are tested using a pilot or prototype network before moving into the Implement phase.

Top-Down Approach

Top-down design simply means starting your design from the top layer of the OSI model and working your way down. Top-down design adapts the network and physical infrastructure to the network application's needs. With a top-down approach, network devices and technologies are not selected until the applications' requirements are analyzed.

Figure 1-3 shows a top-down structure design process. The design process begins with the applications and moves down to the network. Notice that SONA's Network Infrastructure and Infrastructure Services are incorporated into the design process. Logical subdivisions are then incorporated with specifics.

Figure 1-3. Top-Down Design Process

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Table 1-2 compares the top-down approach to the bottom-up approach to network design.

Table 1-2. Top-Down Design Compared to Bottom-Up Design

Design Approach	Benefits	Disadvantages
Top-down	Incorporates the organization's requirements. Provides the big picture. The design meets current and future requirements.	More time-consuming.
Bottom-up	The design is based on previous experience and allows for a quick solution.	May result in inappropriate design. Organizational requirements are not included.

Pilot and Prototype Tests

As soon as the design is complete and before the full implementation, it is a best practice to test the new solution. This testing can be done in one of two ways: prototype or pilot.

A prototype network is a subset of the full design, tested in an isolated environment. The prototype does not connect to the existing network. The benefit of using a prototype is that it allows testing of the network design before it is deployed before affecting a production network.

A pilot site is an actual "live" location that serves as a test site before the solution is deployed to all locations in an enterprise. A pilot allows real-world problems to be discovered before deploying a network design solution to the rest of the internetwork.

With both a prototype and a pilot, successful testing leads to proving the design and moving forward with implementation. A failure leads to correcting the design and repeating the tests to correct any deficiencies.

Design Document

The design document describes the business requirements; old network architecture; network requirements; and design, plan, and configuration information for the new network. The network architects and analysts use it to document the new network changes, and it serves as documentation for the enterprise. The design document should include the following sections:

• Introduction describes the project's purpose and the reasons for the network design.
• Design Requirements lists the organization's requirements, constraints, and goals.
• Existing Network Infrastructure includes logical (Layer 3) topology diagrams; physical topology diagrams; audit results; routing protocols; a summary of applications; a list of network routers, switches, and other devices; configurations; and a description of issues.
• Design contains the specific design information, such as logical and physical topology, IP addressing, routing protocols, and security configurations.
• Proof of Concept results from live pilot or prototype testing.
• Implementation Plan includes the detailed steps for the network staff to implement the new installation and changes.
• Appendixes contains additional information and configurations