My interpretation is, although netmasks (arguably) still exist, there is little use for them in IPv6. (shamelessly copied from http://en.wikipedia.org/wiki/Subnetwork#Subnetting_in_IPv6_networks) Subnetting in IPv6 networks The primary reason for subnetting in IPv4 was efficient utilization of the relatively small address space available, particularly to enterprises. Subnetting is also used in IPv6 networks. However, in IPv6 the address space available even to end-users is so large that address space restrictions no longer exist. The smallest recommended allocation to an end-user is an address space of 80 bits (prefix /48) or in some cases 64-bits (prefix /64) for smaller networks. An IPv6 subnet always has the size of 64 bits intended for the host portion of the address. Although technically possible, smaller subnets are impractical because of the methods used for stateless autoconfiguration of network interfaces (RFC 4862). Subnetting, based on the concepts of Classless Inter-Domain Routing is however used in the routing aspects between networks. http://en.wikipedia.org/wiki/Subnetwork http://wiki.linuxquestions.org/wiki/IPv6_deployment:addressing http://www.pkmz.com/uploads/manuals/ipv6.pdf hope that helps...