Hi Lazaros,
The hierarchical nature of IP addressing is addressed in the subnetting lesson, while the specific feature that helps to keep routing tables smaller is route summarization.
I read the lessons, and I agree that the subjects subnetting/summarization are there. But my intention with my previous suggestion was not to discuss the technical definitions, how to split prefixes, etc. This is important (especially for Cisco certifications), but the definitions (only) do not explain why hierarchical IP allocation is important and what are the design principles behind it.
Instead, I was proposing to explain (using examples) that IP was built to be hierarchical by design. On the Internet, IP allocation is hierarchical. And this is a great advantage over switching when thinking about scalability.
I think it’s worth to introduce the design/architecture concepts regarding hierarchical routing, with good examples, as soon as possible. And I think this first introductory lesson is the ideal place to put that explanation (if not, in another and independent lesson). So people will start to understand this important concept.
My idea is just to introduce the concept of hierarchical routing with one or two examples and explain why it’s good and its advantages over switching. Not just having the definitions of subnetting/summarization.
Side note: Lesson Introduction to Route Summarization is great! You did a great job explaining advantages like summarization saves CPU cycles. But lesson focus on the feature, and although explain advantages, doesn’t demonstrate that IP was built with hierarchical routing in mind, doesn’t provide examples that shows that Internet works this way (hierarchical routing, with bigger routes at borders, and smaller routes closer to “final users”), and doesn’t explain that Internet is possible only because routes are hierarchical. So, although lesson is great, I still think you would add a lot of value introducing the concept of hierarchical routing with one or two examples, and explaining why it’s important and it’s a basic IP principle.
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Side notes:
In practice, lots of people don’t understand this (they understand summarization as a feature, but they do not necessarily comprehending why it’s important and why it should be used) and do not plan networks with hierarchical routing in mind. What I see in practice is lots of /24 networks being allocated without any criteria, making impossible to aggregate afterwards, and generating a lot of scalability problems due to huge routing tables (or cost problems, because now every router needs to be big/expensive in order to process the big route tables).
Even talking about BGP, usually I have to explain people that there is a very good reason why BGP requires routes to be at minimum /24, and that it doesn’t mean that you must only use /24 (if you can summarize to /20 or /21, you should).