If I assign 4M /48's of IPv6 (one to each cable modem on my
network), according to the HD-ratio I am justified to obtain
something around a /20 of IPv6 addresses. In other words, I am
justified in getting 268M /48's even though I am only
using 4M of
them. That would be enough for me to assign at least two for
every household in the US (not just the 19M on my network).
Anyhow, you can see where this might lead...
Yes, towards a rethinking of whether the HD ratio is an appropriate way
to measure the size of an ISP's second allocation.
If one does the math, giving every home user a /56 instead of
a /48 provides almost two orders of magnitude more headroom
in terms of address usage. And at what cost? Surely, everyone
will agree that giving a /56 to home sites is more than
enough space for the foresable future! That's enough for 256
subnets per home site! That's an incredible amount of address space!
And since it is very rare for a home site to change into a non-home site
while under the same ownership/occupancy, the rule of /56 for home users
maintains the same-size-for-all philosophy that was suggested with /48
blocks. A home user can move across town to another residence, hook up
to another ISP and be reasonably guaranteed to get another /56.
That leads me to
doubt that the specific propoasl that was mentioned that
started this thread will actually get much traction within
ARIN, but that is not my problem. :-)
Nevertheless, a lot of this controversy around IPv6 addressing is not
very well informed and is often based on IPv4 architecture, not IPv6.
There is a gap in education here, and due to the scramble to deal with
the imminent runout of IPv4 addresses, people don't have time to get
properly educated. This is a scenario in which informed guidelines from
the IETF would have great value even if they cannot be prescriptive.
I find the fact that RFC 3177 has not been revised to reflect
the reality of today is a bit disapointing.
Precisely! At one time the IETF put some effort into producing IPv6
educational material but that effort seems to have faded away.
And, FWIW, I was one of those that pushed for the changes.
As one who originally supported of the /48 recommendation in
RFC 3177, I think it was a mistake. Giving a /48 to every
home user by default is simply not managing the address space
prudently. Home users will do more than fine with a /56.
I agree. What I don't agree about is the idea that /56's should go to
small sites, i.e. that the ISP makes some judgement about how many
subnets a business might need, and then decide whether or not to give
them a /48 or a /56. Technically, the ARIN policy wording allows for
this.
--Michael Dillon
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