Network Design Blog

7 abril 2009

Network design methodology – Cisco PPDIOO -

Filed under: Uncategorized — antoniopezuela @ 2:33 PM

Cisco has formalized a network’s life cycle into six phases:  Prepare, Plan, Design, Implement, Operate, and Optimize.

Prepare (Identify network requirements)

The prepare phase establishes organization and business requirements, develop network strategy, and proposes a high level architecture to support the strategy. This phase creates a business case to establish a financial justification for a network strategy.

The steps to identify customer requirements are as follows:

  • Identify network applications and services.
  • Define the organization goals (new customer services, reduce cost,…)
  • Define the possible organizational constraints (Budget, personnel, policy and schedule)
  • Define the technical goals. (Improve the network’s response time, simplify network failures, improve network security, improve the network’s scalability,…)
  • Define the possible technical constreints. (Legacy equipment, Legacy applications, …)

Plan(Characterize the existing network)

The Plan phase identifies the network requirements by characterizing and assesing the network, perfoming a gap analysis  against best-practice architectures, and looking at the operational enviroment.

Steps for gathering information:

  • Indentify all existing information and documentation. User imput.
  • Perform a network audit.
  • Use traffic analysis to augment information on applications and protocols used.

When performing a network audit, you have three sources of  information:

  • Existing documentation.
  • Existing network management software.
  • Network management tools.

The network audit should provide the folowing information:

  • Network device list.
  • Hardware models.
  • Software revisions.
  • Configurations.
  • Auditing tool output information.
  • Interface speeds.
  • Link, Cpu, and memory utilization.
  • Wan technology types and carrier information.


Design the Network  Topology an solutions (Design phase)
The network design is developed based on technical and business requirements obtained from the previous phases. The network design include network diagrams and an equipment list.

  • Top-Down approach. You start your design from the top layer of the OSI model and working you way down. Top-down design adapts the network and physical infrastructure to the network application’s need.

Incorporate the organization’s requirements, provide the big picture and the design meets currents and future requirements. (but it’s more time-consuming).

  • Bottom-up. The design is based on previous experience and allows for a quick solutions but may result in innappropiate design (organizational requirements are not included).

As soon as the design is complete and before the full implementation, it’s a best practice to test the new solution:

  • A prototype network is a subset of the full design, tested in an insolated enviroment.
  • 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.

The design document describe the business requirements; old network architecture; network requirements; and designs, plan and configurations information. It should include the following section:

  • Introduction
  • Design requirements.
  • Existing network infraestructure.
  • Design. (logical and physical topology, IP addressing, routing protocols, and security configurations)
  • Proof of Concept.
  • Implementation plan include the detailed steps for the network staff to implement the new installation an changes.
  • Appendixes.

Implement Phase

New equipment is installed and configured in the implement phase. Each step in the implementation should includes a description, detailed implementation guidelines, estimated time to implement, rollback steps in case of a failure, and any additional reference information. As changes are implementd they are also tested before moving to the Operate phase.

Operate Phase.

The Operate phase maintains the network’s day-to-day operational health.

Optimize Phase

The optimize phase involves proactive network management by identifying and resolving issues before they affect the networl.

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