AS13335 Cloudflare, Inc.
2400:cb00:137::/48 - CLOUDFLARE_2400_CB00_0000_36
inet6num: 2400:cb00::/36 netname: CLOUDFLARE_2400_CB00_0000_36 descr: Cloudflare, Inc. descr: 101 Townsend Street, San Francisco CA 94107 country: US admin-c: CTC17-AP tech-c: CTC17-AP status: ALLOCATED NON-PORTABLE mnt-by: MAINT-CLOUDFLARE-AP mnt-irt: IRT-CLOUDFLARE-AP last-modified: 2017-09-07T22:20:55Z source: APNIC role: Cloudflare Technical Contact address: 101 Townsend Street, San Francisco CA 94107 country: US phone: +1-650-319-8930 e-mail: firstname.lastname@example.org admin-c: CTC17-AP tech-c: CTC17-AP nic-hdl: CTC17-AP notify: email@example.com mnt-by: MAINT-CLOUDFLARE-AP last-modified: 2017-09-07T21:57:11Z source: APNIC irt: IRT-CLOUDFLARE-AP address: Cloudflare, Inc. address: 101 Townsend Street, San Francisco CA 94107 e-mail: firstname.lastname@example.org abuse-mailbox: email@example.com admin-c: CTC15-AP tech-c: CTC15-AP auth: # Filtered mnt-by: MAINT-CLOUDFLARE-AP notify: firstname.lastname@example.org irt-nfy: email@example.com last-modified: 2017-09-07T22:11:10Z 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.