Simplification is a constant theme not only here, and in my talks, but across the network engineering world right now. But what does this mean practically? Looking at a complex network, how do you begin simplifying?
The first option is to abstract, abstract again, and abstract some more. But before diving into deep abstraction, remember that abstraction is both a good and bad thing. Abstraction can reduce the amount of state in a network, and reduce the speed at which that state changes. Abstraction can cover a multitude of sins in the legacy part of the network, but abstractions also leak!!! In fact, all nontrivial abstractions leak. Following this logic through: all non-trivial abstractions leak; the more non-trivial the abstraction, the more it will leak; the more complexity an abstraction is covering, the less trivial the abstraction will be. Hence: the more complexity you are covering with an abstraction, the more it will leak.
Abstraction, then, is only one part of the solution. You must not only abstract, but you must also simplify the underlying bits of the system you are covering with the abstraction. This is a point we often miss.
Which returns us to our original question. The first answer to the question is this: minimize.
Minimize the number of technologies you are using. Of course, minimization is not so … simple … because it is a series of tradeoffs. You can minimize the number of protocols you are using to build the network, or you can minimize the number of things you are using each protocol for. This is why you layer things, which helps you understand how and where to modularize, focusing different components on different purposes, and then thinking about how those components interact. Ultimately, what you want is precisely the number of modules required to do the job to a specific level of efficiency, and not one module more (or less).
Minimize the kinds of “things” you are using. Try to use one data center topology, one campus topology, one regional topology, etc. Try to use one kind of device (whether virtual or physical) in each “role.” Try to reduce the number of “roles” in the network.
Think of everything, from protocols to “places,” as “modules,” and then try to reduce the number of modules. Modules should be chosen for repeatability, functional division, and optimal abstraction.
The second answer to the original question is: architecture should move slowly, components quickly.
The architecture is not the network, nor even the combination of all the modules.
Think of a building. Every building has bathrooms (I assume). All those bathrooms have sinks (I assume). The sinks need to fit the style of the building. The number of sinks need to match the needs of the building overall. But—the sinks can change rapidly, and in response to the changing architecture of the building, but the building, it’s purpose, and style, change much more slowly. Architecture should change slowly, components more rapidly.
This is another reason to create modules: each module can change as needed, but the architecture of the overall system needs to change more slowly and intentionally. Thinking in systemic terms helps differentiate between the architecture and the components. Each component should fit within the overall architecture, and each component should play a role in shaping the architecture. Does the organization you support rely on deep internal communication across a wide geographic area? Or does it rely on lots of smaller external communications across a narrow geographic area? The style of communication in your organization makes a huge difference in the way the network is built, just like a school or hospital has different needs in terms of sinks than a shopping mall.
So these are, at least, two rules for simplification you can start thinking about how to apply in practical ways: modularize, choose modules carefully, reduce the number of the kinds of modules, and think about what things need to change quickly and what things need to change slowly.
Throwing abstraction at the problem does not, ultimately, solve it. Abstraction must be combined with a lot of thinking about what you are abstracting and why.