In addition to knowing the essential features of a flexible network, a network designer should also follow a methodology that must guide the entire lifecycle of the design process. In this regard, Cisco developed the PPDIOO model, which is a six-phase model that every network implementation will go through during its operational lifetime, as follows:
- Prepare
- Plan
- Design
- Implement
- Operate
- Optimize
The PPDIOO lifecycle model (Figure 2.4) and SONA have one common benefit: they both lower the TCO. In the early phases of the process, technology requirements are evaluated and validated, which allows for proper planning in response to changes in the infrastructure and requirements for resources. It also improves network availability by using a solid network design, and along the way, network operations are validated. In addition, it makes the company more agile by establishing business requirements and technology strategies and adjusting them on a regular basis. Finally, it speeds access to applications and services by improving the following issues:
- Availability
- Scalability
- Performance
- Reliability
- Security
Figure 2.4 – PPDIOO Lifecycle Model
The network’s lifecycle might not go through these six phases in this particular order without some type of iterative process. For example, after the implementation phase, you might need to go back to the planning or design phase and make some changes at that level. It can also be an iterative process where the flowchart can be modified based on changing technologies, budget, infrastructure, business needs, or business structure. Unplanned actions can happen, especially in the operation phase. Each phase is covered in detail below:
- Prepare Phase: The first phase of PPDIOO is the prepare phase. This is where you establish the company’s requirements and goals. The IT and the network/security infrastructure must always be in line with the company’s goals and business requirements. At this stage, a network strategy and high-level architecture to support that strategy is developed. Possible technologies that can support that architecture must be identified. A business case must also be established in order to have a financial justification for the overall network strategy. Representations from the company’s board of directors (CIO, COO, etc.) might be involved in this phase.
- Plan Phase: Planning is the most underutilized phase in the PPDIOO process. This includes identifying the decision- and policy-makers, and determining the fundamental network requirements (who needs what services and when). The plan phase is where the entire information gathering process is completed, and the network and security requirements are identified, as well as identifying the legislation to which the company or its customers must adhere (SOX, HIPAA, etc.).
The network security system lifecycle must be analyzed carefully, including the company’s needs and risk analysis. The security policies, guidelines, and processes must be evaluated, along with the security system that is in place or with possible future security system acquisitions, such as the Cisco Adaptive Security Appliances (ASAs). Planning also includes the study of best practices and case studies, and then putting into place the security operations, responses, monitoring, and compliance.
The network management processes also must be considered in this phase because they are closely related with the network infrastructure. This includes fault management to detect and correct specific problems; configuration management that helps in establishing a network baseline and in developing a configuration tracking process (for networking appliances and devices); accounting management that keeps track of circuits for billing of services; performance management to monitor the network’s effectiveness in delivering packets; and security management (AAA – RADIUS/TACACS+ protocols).
In the plan phase, you will characterize the network and perform an analysis against best-practice architectures, and look at the operational environment overall. A project plan must be created in order to help manage the tasks, identify the responsible parties or individuals, set the milestones, and identify the resources needed for the design and implementation of the project. This generated project plan must be followed through the remaining phases of the PPDIOO lifecycle.
- Design Phase: The next phase involves designing the network according to the company’s policies, procedures, business goals, and available budget and technologies. The design phase also might mean meeting with policy-makers, team leaders, and end-users in the process of gathering and analyzing data, and auditing all key activities. Results of the design phase are the basis for the approach taken in the next phase, which involves implementation. The focus of the CCDA blueprint is comprised of the first three PPDIOO phases – prepare, plan, and design – among which the design phase is the most complex. As such, the design phase will be covered in more detail later in this chapter and in the remaining chapters of the manual.
- Implement Phase: The competitive nature of business, and the rush to market products and services, forces many organizations to skip the first three phases of the PPDIOO lifecycle model and start with the implement phase. Many times, those companies become stuck in this phase because of a lack of planning and design. The implement phase involves constructing the network infrastructure with the best affordable technologies based on all the design specifications.
The implement phase includes configuration, installment, maintenance, and so on. This is where the new equipment is installed and configured using the command line interface (CLI) or graphical tools (SDM, ASDM, etc.). Old devices might be replaced with new devices, or some components might be upgraded (memory, operating systems, etc.). The project’s plan must be followed during the implement phase. Planned network changes should occur here, and they should be communicated through control channels in meetings and receive the appropriate approvals.
Each step in the implement phase should have a description, detailed implementation guidelines, a time estimate, and instruction steps for falling back to a previous state in case something goes wrong. It will also combine additional reference information, from either RFCs, white papers, case studies, or other Cisco documentation. Any changes implemented here should be tested before moving on to step 5 – the operate phase.
- Operate Phase: The operate phase is the final proof that the network design was implemented properly. Performance monitoring, fault detection, and operational parameters will be confirmed in this phase. This will also provide the data used for the final phase.
This phase involves maintaining the day-to-day operational maintenance and health of the network infrastructure. This includes managing the network components, monitoring, conducting analysis and creating reports, routine maintenance, managing the upgrades of the systems (hardware, software, of firmware), managing performance, and identifying and correcting any network faults or security incidences. This final test of the design process involves analyzing the actual operations of the implemented network system. Network management stations (NMSs) should monitor network health parameters, through SNMP traps (and certain thresholds reached) or other real-time monitoring solutions.
- Optimize Phase: Optimizing involves proactive and aggressive management and control over the network. Problems must be identified quickly so that troubleshooting can take place to assure fault detection. This phase is crucial because it is often followed by another planning or design session in order to redesign the implementation, which makes these phases all the more important. Much time and money might be invested into the optimize phase if some failures occur in the initial planning and design phases.
Optimization refers to proactive network management, meaning identifying and resolving issues before they move throughout the entire network. The optimize phase might also generate a modified network design if too many problems appear in the implement and operate phases. Sometimes, you might need to go back to the design phase in order to solve those problems and implement new solutions.
The goal of this entire process is constant improvement, and the IT Infrastructure Library (ITIL) might be used as a basis for network design and administration.
The following section will focus on the primary goals of a network designer in detailing the design phase and analyzing some design methodologies used in PPDIOO.
A proven method for network design is necessary because it provides consistency in the design process, it offers a framework from which to work, and it assures the network designer that no steps will be left out of the process.