There is an old saying that you should really apply to networking: think before you act. In fact, what separates you from tearing down the entire infrastructure is often a single command. While this is important, today we will focus on network design. Since networks grow organically, you need to plan everything from the beginning. To avoid the worst, you should know the lifecycle of a network. Cisco presents it in the Cisco PPDIOO: Prepare, Plan, Design, Implement, Operate, Optimize. Understanding this lifecycle will help you design beautiful networks. Let’s get started!
What is Cisco PPDIOO?
In short, Cisco PPDIOO is a lifecycle. This already indicates that networks are different from what most people believe. Sometimes, customers think networks are just devices you plop there until they die. You replace faulty devices one by one, as the faults dictate, and you are all set. This approach may even work well for a very static environment but is likely to fall apart in the enterprise.
With Cisco PPDIOO, you keep assessing if the networks still meet the requirements. After all, networks are there for a reason, and you need to evaluate if the reason is still valid. This way, you know early if it isn’t. This means you have the time to plan for changes and upgrades.
Can we translate “Cisco PPDIOO” simply in “Be on watch”? No, PPDIOO goes even further. In fact, it tells you to be alert, but it also tells you how to do that, and how to react to changes.
Cisco PPDIOO Phases
To structure the project of designing and maintaining a network, Cisco divided PPDIOO into phases. Since we are talking about a lifecycle, phases repeat themselves in a circular loop.
We will dive into each phase in detail later, but for now, here is a quick explanation.
- Prepare – This phase is the initial assessment of business needs, and definition of a conceptual architecture
- Plan – At this point, you translate business needs into technical requirements.
- Design – Here, the network design team produces clear network specifications.
- Implement – Once the customer approves the design, network engineers implement it by installing and configuring devices.
- Operate – After the network is created, in this phase the operation team maintains it in the day-by-day.
- Optimize – The operation team can understand identify any issue that arises or that may arise in the future. It may lead again to the Prepare phase in case a new design is needed to face the issue.
According to the size of the network, some phases may blend together. If the network is enterprise-sized, the phases will be distinct, maybe with even different teams working on each. As the network gets smaller, Prepare and Plan may blend into a single process, that may end up including design as well. Operate and Optimize may be the same thing, as long as the optimization does not require a whole new design. Network design is a creative process that must respect a schedule. Because of that, having a clear method like PPDIOO will help you to respect deadlines.
Network design is a creative process that must respect a schedule.
Breaking down Cisco PPDIOO Phases
Prepare
For PPDIOO, Preparation is everything. In this phase, you gain an understanding of the situation on customer’s needs and existing infrastructure. This is crucial because it tells you where to focus. If you don’t get the situation right, you may design something that does not address customer requirements. Failing here means creating a whole project that doesn’t do what the customer expected. To avoid that, assess the requirements, the current network, and define a conceptual architecture.
Assessing Customer Requirements
Customers are no network expert in general. Thus, they will pose you high-level conceptual requirements, that you need to evaluate. In fact, you may even help the customer clarify what he actually needs. If you know what the network is used for, you can plan it right. Because of that, understand what applications will the customer run. For each application, identify these items:
- Application type (like mail, web-browsing, conferencing, etc.)
- Actual application in use (Outlook, Google Chrome, Jabber etc.)
- Importance of the application, and any additional comment
Then, use what you gathered to identify organizational goals. Look for both short- and long-term goals by looking at the company’s activities and processes. Even applications are just means, as the network. Why is the company using these applications? Where are they going? If the company is a large enterprise, requiring a large project, they are likely to know what they need. In fact, they will put this information in a document: the Request for Proposal (RFP), or the Request for Information (RFI).
Knowing the goals is only half of your job. The other half is knowing organizational constraints. Here we are talking about hard limits for the project. Generally, budget and schedule are common constraints. However, you also need to consider the personnel to see if the company has the competencies to run the network. It is also good to understand company policies, particularly in terms of security. You may find some constraints here as well.
Assessing current network infrastructure
Another important item of the PPDIOO Prepare phase is having an understanding of the current infrastructure. This, of course, makes sense only if that infrastructure exists. In fact, the project may require to replace it or to integrate with it.
Identify the major features of a network. These could be the device inventory, the WAN speeds, and the addressing plan. If the network has remote sites, understand how they talk with each other. It is also important to have a site contact in the remote sites to coordinate the shipment and installation of new devices.
You can use tools to help you with the assessment. For example, you can NetFlow to gather information about flows going over the network. Many tools are available for network auditing, you just need to find the one that works best for your needs.
Defining a conceptual design
This is not the design itself. However, once the prepare phase finishes, you should have an idea of what you need to do. Do you need WAN links? Do you need wireless? Is the customer asking for a VoIP setup?
Always produce a deliverable. In other words, finish the phase by writing a document. In that document, list all the requirements and constraints you see. Add to them the conceptual design, that will guide you through the next phase.
Plan
In the PPDIOO plan phase, we translate the customer requirements from the prepare phase in technical requirements. Our goal here is the production of a document that designers can read. This document must tell how the network should be with clarity. The designers must have a clear idea about the technical requirements and do not have to interpret them.
To create this document, you should identify the technical goals. Generally, you can address customer’s needs with technical goals similar to the ones below.
- Improve responsiveness and throughput
- Simplify network management
- Improve security and reliability
- Decrease downtime and related expenses
- Modernize legacy technologies
- Improve scalability
Use the assessment of the existing network to identify technical constraints. Like in the prepare phase, these are hard limits you need to cope with. Often, you will have limits in the following areas.
- Existing equipment, as it has to coexist with the new equipment (at least during migration phase)
- Bandwidth availability, that might come from budget constraints or from other issues like coverage, in case sites are in remote locations
- Application compatibility
Use what you find out at this step to produce a clear set of specifications. If you have too many limits, and can’t produce valid specifications, check with the customer to adjust the goals and constraints with the reality. You may get back to the prepare phase if that is the case.
Design
Since PPDIOO is all about network design, you can imagine the importance of the design phase. Here you need to produce the design document of the network, starting from the specifications. This is the primary goal of network designers. In this document, try to include at least the following items.
- Layer 3 topology, divided into modules if the network is large
- Layer 1 maps
- Audit results (from the prepare phase)
- Summary of services, routing, and applications to implement
- Configuration of existing devices
- Time estimations (for implementation)
The more you detail the design, the fewer skills you will require for the engineers implementing it. With this document in hand, the implementer should know what to do. Of course, use time estimations to allow the customer to benchmark the project. A project manager may be helpful here.
After this phase, the customer will buy the devices. We are ready to start!
Implement
There is little to say regarding the PPDIOO implement phase. The network engineer will take the document and implement it. Here the configuration of the devices happens, but not just that. Cables are laid, and devices are actually installed in racks.
You do not expect any impediment here. If you encounter them, you haven’t planned everything carefully. Obviously, it may happen that you have some delay and that something is more complex than it seemed to be. However, if you followed this process right, here you won’t have any showstopper.
Operate
Depending on the size of the network and the customer requirements, a network will require some operations. Highly independent networks will require at least a team that can respond to the incident: monitor devices, and eventually ask the vendor for replacement in case one fails. To that, you may add additional services like configurations and so on.
In a large enterprise, someone will be needed to configure the ports of switches and to help users troubleshoot connectivity issues. This phase is highly coupled with company policies, and you need to know them well.
Furthermore, by monitoring the network, you can identify problems before they arise. This allows you to do the optimize phase, that would be impossible otherwise.
Optimize
If you are doing the operate phase correctly, you can do the PPDIOO Optimize phase as well. As soon as you see some problems arising, you can identify their entity and react to them. A common task of this phase relates to the bandwidth of WAN links. During the operate phase, you monitor their usage with tools like NetFlow. If they consistently breach a utilization threshold, generally 60%, you start planning for an upgrade. This way, you avoid bottlenecks on the WAN.
You can apply optimization to everything. It could be adding a switch, adding a new module in the data center, switching from single-links to port channels, or implementing a new security feature.
Wrapping it up
At this point, you should have an idea of how network design works. This can help you start your career as a network designer or architect. However, this knowledge is useful even if you just want to stick being a network engineer. Knowing the big picture you are part of is always good!
What do you think about PPDIOO? Are you applying it to your daily job? Have you improved it in some ways? Let me know what you think in the comments!
