An IRR AS-SET is a named collection of Autonomous System Numbers (ASNs) within the Internet Routing Registry (IRR) used to define and manage BGP routing policies. By grouping related networks, such as customers and downstream peers, under a single identifier, network operators can automate the creation of BGP filters, which are essential for preventing the propagation of BGP route leaks. AS-SETs can be hierarchical, meaning they can include other AS-SETs as members, creating a scalable but complex structure. To quantify this complexity, the "AS Cone" measures the total number of unique ASNs in a fully expanded set (its downstream footprint), while "Upstreams" measures how many other AS-SETs include it directly or indirectly, providing insight into its role in the global routing system.
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