“Ex uno plures”: Finding and blocking a spanning set of IP addresses when starting from just one

This blog-style guide explains how to pivot from an IP address to the originating ASN using the University of Oregon Route Views data, how to extract IPv4 and IPv6 prefix lists from MRT RIB files, condense them into minimal covering CIDR sets (using tools like cidrmerge and cidr-merger), and apply those CIDR lists to Debian ufw firewalls via ipset and iptables/ip6tables for blocking or filtering purposes. It includes example commands, tool installation notes, and practical considerations for persistence and capacity.