ISP customer assignments

James Hess mysidia at
Wed Oct 7 00:02:34 UTC 2009

>>  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...


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