The report explains how the outage of a single AS affects the global connectivity of the region, especially when it is the biggest ISP of a given country. Internet connectivity at the network level is driven by the interaction between autonomous systems (AS’s). As the number of alternate routes between AS’s increases, so goes the fault-resistance and stability of the internet in a given country. However, some paths become more important than others and having as many alternate routes as possible is the only viable way ensure the system is adequately robust.
The global connectivity of any AS, regardless of whether it is a minor provider or an international giant, depends on the quantity and quality of its paths to Tier-1 ISP’s. Usually, Tier-1 implies an international company offering global IP transit service over connections to other Tier-1 providers. But there is no obligation to maintain such connectivity. Only the market can motivate them to peer with other Tier-1’s to deliver the highest quality service. Is that motivation enough? We explore this question in the IPv6 section below. If an ISP loses its connection to at least one of its Tier-1 peers, it would likely become unreachable in some parts of the world.