v6 subnet size for DSL & leased line customers

Ross Vandegrift ross at kallisti.us
Sat Dec 22 20:23:17 UTC 2007

On Fri, Dec 21, 2007 at 01:33:15PM -0500, Deepak Jain wrote:
> For example... Within one's own network (or subnet if you will) we can 
> absorb all the concepts of V4 today and have lots of space available. 
> For example... for the DMZ of a business... Why not give them 6 bits 
> (/122?) are we anticipating topology differences UPSTREAM from the 
> customers that can take advantage of subnet differences between /64 and 
> /56 ?

I am confused on this point as well.  IPv6 documents seem to assume
that because auto-discovery on a LAN uses a /64, you always have to
use a /64 global-scope subnet.  I don't see any technical issues that
require this though.  ICMPv6 is capable of passing info on prefixes of
any length -  prefix length is a plain old 8bit field.

In fact, until I read the ARIN documents to receive an assignment at
work, I assumed this would be how people would operate.  So what's the
concern?  Give all end users a /64 and let them subnet that as they
see fit.  If DHCPv6 would take care of it automatically with shorter
prefixes, that's fine - I doubt it cares if it's doling out info for a
/56, /64, or /96.  Not like anything on the public internet is going to
care a lick either.

Ross Vandegrift
ross at kallisti.us

"The good Christian should beware of mathematicians, and all those who
make empty prophecies. The danger already exists that the mathematicians
have made a covenant with the devil to darken the spirit and to confine
man in the bonds of Hell."
	--St. Augustine, De Genesi ad Litteram, Book II, xviii, 37

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