unimaginably huge *classless* network. Yet, 2 hours into day one, a classful boundary has already been woven into it's DNA. Saying it's
No bit patterns in a V6 address indicate total size of a network. v6 doesn't bring classful addressing back or get rid of CIDR.. v6 dispenses with something much older: common use of VLSM on the local LAN and sizing subnets based on the number of hosts. Instead a form of FLSM is recommended, a fixed standard subnet size of /64 that essentially all IPv6 networks use for the subnets that have hosts on them. This restores consistency to LAN addressing. In V4 there is a valid reason for choosing VLSM and sizing every subnet: IP addresses are scarce. V6 removes that scarcity problem. No more unanticipated growth necessitating an addressing re-design, or at least error-prone adjustment of netmasks on all hosts. No more hodgepodge of different netmask settings for different sized LANs. No more LAN address ranges starting or ending with a different trailing string of digits than other LANs. /64 is the standard. V6 leaves the operator able to pick something different, but in most cases it would be a very poor design practice, and ISPs should think long and hard before ignoring the standard and trying to issue a customer subnet a /128, instead of /48 or /56. However... none of the network protocol documents were ever able to prevent determined people from coming up with bad designs, or ignoring recommendations due to politics or preconceived notion(s); don't hold your breath on that one... -- -J