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Choose Simple Solutions

In my experience, simplicity is not valued enough in software development. Instead, there is a lot of emphasis placed on flexibility. —Felix

Replace “software” with “network,” and think about it. How often do network engineers select the chassis-based system that promises to “never need to be replaced?” How often do we build networks like they will be “in use” 20+ years from now? Now it does happen from time to time; I have heard of devices with many years of uptime, for instance. I have worked on AT&T Brouters in production—essentially a Cisco AGS+ rebranded and resold by AT&T—that were some ten or fifteen years old even back when I worked on them. These things certainly happen, and sometimes they even happen for good reasons.

But knowing such things happen and planning for such things to happen are two different mindsets. At least some of the complexity in networks comes from just this sort of “must make it permanent: thinking:

Many developers like to write code which handles any problem which might appear at any point in the future. In that regard, they are fortune tellers, trying to find a solution for eventual problems. This can work out very well if their predictions are right. Most of the time, however, this flexibility only causes unneeded complexity in the code which gets in the way and does not actually solve any problems. This is not surprising as telling the future is a messy business.

Let’s refactor: many network engineers like to build networks that can handle any problem or application that might appear at any point in the future. I know I’m close to the truth, because I’ve been working on networks since the mid- to late-1980’s.

So now you are reading this and thinking: “but it is important to plan for the future.” You are not wrong—but there is a balance that often is not well thought out. You should not build for the immediate problem ignoring the future; down this path leads technical debt. You should not plan for the distant future, because this injects complexity that does not need to be there.

How do you find the balance? The place to begin is knowing how things work, rather than just how to make them work. If you know how and why things work, then you can see what things might last for a long time, and what might change quickly.

When you are designing a protocol, does it make sense to use TLVs rather than fixed length fields? Protocols last for 20+ years and are used across many different network devices. Protocols are often extended to solve new problems, rather than being replaced wholesale. Hence, it makes sense to use TLVs.

When you are designing a data center or campus network, does it make sense to purchase chassis boxes that are twice as large as you foresee needing over the next three years to future proof the design? Hardware changes are likely to make a device more than three years old easier to replace than upgrade—if you can even get the parts you need in three years. Hence, it makes more sense to plan for the immediate future and leave the crystal ball gazing to someone else.

If you haven’t found the tradeoffs, then you haven’t looked hard enough.

But to look hard enough, you need to go beyond the hype and “future proofing,” beyond how to make things work. You need to ask how and why things work the way they do so you know where to accept complexity to make the design more flexible, and where to limit complexity by planning for today.

1 Comment

  1. Steve on 1 April 2019 at 11:32 am

    People also need to think of the real cost of “future proofing”. Every unused port is stranded capital, getting that license to cover every possible feature that you don’t use today is the same thing. The network should be flexible, but your wasting your companies money and your time deploy for events that may happen 3 years in the future. The present value of the extra line cards that you might use years after the purchase is very high and should factor into any future proofing.

    This is of course different than if you have high probability plans of using these extra bits, but often we make decisions off of maybes that hide the true costs of future, unplanned expansion.



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