Re: ISP customer assignments

[Michael Dillon]

> He didn't really give much of a reason for the /127s yet.  I think it's
> coming up in a later session.  I think it basically boiled down to whether
> or not the customer would actually use anything bigger.  I'll write back
> 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 you
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 that
there policy allows for a /56 or a /48 to be assigned to residential customers,
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