[118171] in North American Network Operators' Group
Re: ISP customer assignments
daemon@ATHENA.MIT.EDU (Michael Dillon)
Tue Oct 13 14:40:43 2009
In-Reply-To: <4AD4818F.1060701@justinshore.com>
Date: Tue, 13 Oct 2009 19:40:01 +0100
From: Michael Dillon <wavetossed@googlemail.com>
To: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
> He didn't really give much of a reason for the /127s yet. =A0I think it's
> coming up in a later session. =A0I think it basically boiled down to whet=
her
> or not the customer would actually use anything bigger. =A0I'll write bac=
k
> when we get into that discussion.
As a service provider, you do not have any control over the customer's
environment.
As a starter, that means sticking to the /64 per subnet boundary because yo=
u
don't really know whether a customer might need some devices which assume
EUI-64 interface addressing.
But when you look at the source of your addresses, the RIRs, you will see t=
hat
there policy allows for a /56 or a /48 to be assigned to residential custom=
ers,
your choice. So, why would you want to use longer prefixes?
Admittedly, in an enterprise environment where you have total control over
the devices on the network, it may be reasonable to use /127s and other
odd prefix lengths. But only if you actually have a reason. Not wasting
addresses is not a reason, and any IPv6 architectural decisions driven by
not wasting addresses, are not reasonable decisions. It is fundamental to
IPv6 to use large address blocks that can never possibly be used up,
in order to design a network where your design decisions are based
on solid technical reasoning, and that design can remain unchanged even
if you massively scale up the number of devices on your network.
--Michael Dillon
