AS11644 Núcleo de Inf. e Coord. do Ponto BR - NIC.BR
2001:12f8:4::/48 - FAN4
inetnum: 2001:12f8:4::/47 status: assigned owner: Núcleo de Inf. e Coord. do Ponto BR - NIC.BR city: São Paulo country: BR owner-c: FAN4 tech-c: FAN4 abuse-c: FAN4 inetrev: 2001:12f8:4::/47 nserver: A.DNS.BR nserver: B.DNS.BR nserver: C.DNS.BR nserver: D.DNS.BR nserver: E.DNS.BR created: 2017-11-29 changed: 2017-11-29 source: LACNIC
IP address ranges, or netblocks, are groups of related IP addresses. They are usually represented as a base IP address, followed by a slash, and then a netmask which represents how many IP addresses are contained within the netblock. This format is known as CIDR. You'll also sometimes see netblocks given as a start ip address, and an end ip address, or an ip address range.
Traffic works its way around the internet based on the routing table, which contains a list of networks and their associated netblocks.