AS17832 Korea Internet Security Agency
2001:2b8:51::/48 - KRNIC-NET
inet6num: 2001:2b8::/32 netname: KRNIC-NET descr: Korea Internet Security Agency country: KR admin-c: IM574-AP tech-c: IM574-AP status: ALLOCATED PORTABLE mnt-by: MNT-KRNIC-AP mnt-irt: IRT-KRNIC-KR last-modified: 2017-01-03T07:46:34Z source: APNIC irt: IRT-KRNIC-KR address: Seocho-ro 398, Seocho-gu, Seoul, Korea e-mail: firstname.lastname@example.org abuse-mailbox: email@example.com admin-c: IM574-AP tech-c: IM574-AP auth: # Filtered mnt-by: MNT-KRNIC-AP last-modified: 2017-10-19T07:36:36Z source: APNIC person: IP Manager address: Jeollanam-do Naju-si Jinheung-gil country: KR phone: +82-2-405-5118 e-mail: firstname.lastname@example.org nic-hdl: IM574-AP mnt-by: MNT-KRNIC-AP last-modified: 2017-07-27T05:56:18Z source: APNIC
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.