IPv6 addresses are 128 bits long. One key architectural shift with IPv6 is the fixed boundary between the network and host portions of an address, which is set at /64. Eliminates ambiguity around subnetting, routing continues to work by prefix, just as it did with CIDR under IPv4, but routers are not required to examine all 64 bits of the network portion.

IPv6 Address Notation: The Basics

An IPv6 address is expressed as 8 groups of 16 bits, separated by colons. For example: