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Here are some examples of conditions that demonstrate the complex nature of the Internet:

Slammer worm

Source: Jon Crowcroft, Mark Handley [1]: "The worm attacks end systems and is an example of a scanning system that propagates very rapidly exploiting code weaknesses in end-systems, together with lists of addresses to visit next. The problem that showed up in this particular case was that the end systems were often routers (normally one considers a router as an intermediate system, but when traffic is directed to the router itself, it should be thought of as an end system). Some routers were so inundated with traffic that they were unable to compute and send routing updates to their neighbours. The net effect of this is that they are “dropped” from routing tables, and so connectivity starts to fail. This interaction between end system role and intermediate system role (control plane and data plane) shows up as an emergent property, which is that the network starts to partition."

BGP prefix damping

Source: RIPE-378: "The major issue is that if one path is withdrawn, all BGP speakers will use best path selection to pick the next best path, and advertise this best path to all their neighbours. These neighbours will see a change in path; a change in path is a change in attribute, so the prefix as seen on a neighbouring router will attract a flap penalty - even though that path is perfectly valid and there has been no disappearance of the prefix from the routing table [5]. And this path "hunting" goes on throughout the Internet - a simple prefix withdrawal can result in the appearance of a major flap event a few AS hops away in the Internet, with the result that vendor default and even the RIPE-229 recommended flap damping parameters will mark the prefix to be suppressed. While the operator can see this is an error, the routers are simply reacting to the circumstances presented to them."

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