2001:420:5a00::/39 - CISCO-IPV6-1
V6NetHandle: NET6-2001-420-1 OrgID: CISCOS-2 Parent: NET6-2001-400-0 NetName: CISCO-IPV6-1 NetRange: 2001:420:: - 2001:420:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF NetType: allocation RegDate: 2000-06-14 Updated: 2018-05-13 Source: ARIN OrgID: CISCOS-2 OrgName: Cisco Systems, Inc. CanAllocate: Street: 170 West Tasman Drive City: San Jose State/Prov: CA Country: US PostalCode: 95134 RegDate: 1986-02-05 Updated: 2018-09-27 OrgTechHandle: GATC-ARIN OrgTechHandle: BRAEC-ARIN OrgAbuseHandle: DN5-ORG-ARIN OrgAdminHandle: GATC-ARIN OrgTechHandle: ZIEGL31-ARIN OrgNOCHandle: GATC-ARIN Source: ARIN
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.