[117938] in North American Network Operators' Group
Re: ISP customer assignments
daemon@ATHENA.MIT.EDU (James Hess)
Tue Oct 6 20:03:44 2009
In-Reply-To: <20091006133613.GA5059@dan.olp.net>
Date: Tue, 6 Oct 2009 19:02:34 -0500
From: James Hess <mysidia@gmail.com>
To: Dan White <dwhite@olp.net>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
>> =A0unimaginably huge *classless* network. =A0Yet, 2 hours into day one, =
a
>> =A0classful boundary has already been woven into it's DNA. =A0Saying 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 t=
hem.
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
