Network Design Process - Part 2

In my last blog, I mentioned an e-mail discussion I had with a new network design engineer in Germany. In that blog, I discussed Cisco's PDIOO model and the "Planning" phase of a network design.

As with the "Planning" phase, I cannot cover every aspect of network design in blog, but I will try to provide a bullet list of tasks in the "Design" phases using the guidelines of Top-Down Network Design.

Design

• Read the Requirements Again - you probably spent a good time in the Planning phase and, hopefully, took good notes. Well, make sure you read those notes and documents; several times. The last thing you want to do is design a network, order equipment and circuits, and then find out you missed some of the requirements.
• Break the Design into Modules - If it's a large network design - let's say a campus or a data center - break the design into manageable modules. Getting an entire campus design in a single diagram is impossible, or at least useless to a user. Think about how your network will go together and then break down the network into sections that can be designed separately.
• Use Templates - a good network architect should have developed templates for you to use. Most network designs are repeatable - few require completely new designs (completely new design should be immediately made into templates). Find the template that most fits your customer's requirements and use it.
• Draw out the Traffic Flows - understanding traffic flows is key to any network design. And, in the spirit of documenting everything, draw out the traffic flows. This will give you a good idea of how the network design will support the users and applications.
• Design in Levels - a good network design should include a High Level Design (how the new network fits into the existing network), Physical Design (hardware types, ports, cables, etc), Logical (VLANs, IP addressing), and Layer-3 Routing (routing protocols, static routes). Design each of these levels independently, with the understanding they all work together. :-)
• Procure WAN Service - while WAN services are part of the "Design in Levels" process, they require a separate step because they have their own characteristics, the big one being they have to be ordered, usually 60-90 days out. Cost, technology type, bandwidth levels, handoff, contracts, and security all need to be considered.
• Evaluate Security at all Levels - enough said.
• Develop the Network Management Plan - if the customer does not have existing network operation tools and processes, you will need to develop them as part of the network design. The customer must be able to monitor the network day-to-day and be able to evaluate the network design. If they have an existing network management platform, understand how your new network will be managed by this platform.
• Conduct a Peer Review - get other engineers to review your design. No one is perfect. You will make mistakes or miss things. Plus, it makes the customer more comfortable to know a team has reviewed the design, not a single person.
• Test, Test, Test - at a minimum test all network aspects (routing, interfaces, traceroute, ping, etc). If possible, run the customers application over the network. Be sure to test outage conditions and convergence times.
• Develop Implementation Plan - how will the new network actually be implemented? This should explain what will happen to the existing network, what outages will occur, and expected timelines. This will allow the customer to gauge impact and schedule the implementation.
• Present the Design to the Customer - actually, you should be keeping the customer informed during the entire process. Do not wait to the last step to show the customer what you've done. However, at the end, there should be a formal presentation on all aspects of the design and a final approval to implement.

This is a simple process to follow for network design. Adding in good technology skills will produce great networks.