Our inference algorithm relies on public BGP data from RouteViews and RIPE RIS. Importantly, per the figure, we do not infer an AS's
customer cone based on paths observed directly from that AS. Rather, we use paths observed from the peers and providers of the
AS in question. The reason for this filtering is that an AS selectively announces paths: to its customers, it may announce everything,
but to its "upstream" providers or peers ASes, it will announce only paths to its customers. Thus, we need to observe a
path through one of the AS's inferred providers or peers in order to infer the destination prefix (and its origin AS) is in the customer cone of that AS.
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