Comment by dredmorbius

Adding to this, Autonomous Systems, which are identified by ASNs, are the networks that the Internet is internetworking between.

That protocol is called BGP, or border gateway protocol. Most people's familiarity with that initialism, if any, comes from reports of major outages which occur when BGP routing --- effectively the list of peers to which a given AS connects --- gets fuxnored. This happens with somewhat distressing regularity (though not exceptionally high frequency), and along with some other notable failure points in modern telecoms (say, SIM spoofing, DDoS, or good old social engineering) is not-so-charmingly naive in its architecture of implied trust and lack of technical safeguards against either accident or malice.

As originally specified, ASNs ranged to 65,536 distinct systems (16 bits). That's since been bumped up to 32 bits, for 4,294,967,296 distinct systems.

Some old hands would track network abuse by ASN or a somewhat finer gradation, CIDR (classless internet domain routing), which tend to aggregate poorly-behaved networks into identifiable aggregates. That was somewhat more tenable with the smaller number of providers, though power laws and Zipf functions mean that bad behaviour does stil tend to self-organise in useful ways. Growth in indirection (VPNs and Tor) challenge this somewhat, with gateways now being identified as abuse sources, which is ... problematic.