The Elusive Internet Flattening: 10 Years of IXP Growth


Over the past decade, IXPs have been playing a key role in enabling interdomain connectivity. Their traffic volumes have quickly become similar to those of Tier-1 ASes and their physical presence has spread across the world. While the relevance of IXPs is undeniable, their contribution to the shaping of the current Internet is not fully understood yet, especially on the so-called “flattening” phenomenon. In this paper, we disentangle “flattening” from “path shortening”: we show that the impact of IXPs on path-length is limited. Surprisingly, Internet path-lengths have globally barely decreased over the last decade, regardless of whether they cross IXPs or not. Instead of a “path-shortening”, we observe a diversion of the routes away from the central Tier-1 ASes, supported by IXPs. This diversion has however not fundamentally changed the existence of a hierarchy, but rather replaced the central Tier-1s with a new set of players.

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