[ppml] IPv6 & /48 [was 2005-1:Business Need for PI Assignments]

william(at)elan.net william at elan.net
Mon Apr 25 17:08:29 EDT 2005

On Mon, 25 Apr 2005, Randy Bush wrote:

> just to throw in a serious bomb, there is no actual real technical
> reason for the /64 magic boundary.  it's one of the last big pieces
> of the old v6 religion.  but beware that it does have some ties to
> ether-like mac addresses and hence auto-numbering.

I think early on people talked about having 64-bit ip addressed and then
talked about easy load-balancing and allowing multiple devices to have same
64-bit internet (ISP assigned) ip address with multiple actual devices at 
the end that have different physical addresses. That ended up being 128bit 
address with first 64bits designated for internet routing and last 64bits 
being unique device id. Entire 64bit for device id is because currently we 
use /48 MACs and extra /16 was added just in case as well as to allow for 
different MAC-like (or not like) device-id addressing systems (and BTW 
with /48 bits there and many more network cards sold then we have internet-
connected machines we still have not come close to exhausting those addresses)
Now possibly future astronauts and nanotech-engineers will find a better 
use for those last /64 bits (and they will then thank use for leaving 
those 64 bits open) but lets not worry about that right now because the
most important thing we need to do is to actually help get ipv6 deployed.

As far as why /48 for end-networks that was decision done not only by IETF 
but also discussed at all RIRs - I remember we had voted for that on at 
least two ARIN meetings in around 2000-2002 (I think Las Vegas was when it 
was finalized) and there was a consensus about it. It can be changed, but 
it'd have to be the same kind of process with everyone getting involved 
and agreeing on the change and it would cause yet another push of ip6 
deployment by several years. Plus I really don't see why we should be 
worrying about it when just for case like that it was decided that only 
1/4 of ipv6 space will actually be open for use and rest 3/4 are reserved 
in case we ever actually exhaust the first 1/4 and then if we do we can 
surely work out a lot more serious policies as to how not to exhaust 
remaining 3/4 quickly...

William Leibzon
Elan Networks
william at elan.net

More information about the ARIN-PPML mailing list