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

Marshall Eubanks tme at multicasttech.com
Mon Apr 25 18:16:32 EDT 2005

On Mon, 25 Apr 2005 14:08:29 -0700 (PDT)
 "william(at)elan.net" <william at elan.net> wrote:
> 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.

I think that IPv6 embedded RP multicast has shown that you can do cool things
in IPv6 because you can embed an address (with some restrictions)
completely inside of another one. 
(In embedded RP, what's embedded is the address of the RP for the multicast
group, which means that interdomain ASM multicast can be done without a raft of protocol
infrastructure, like MSDP.) 

I have a feeling that people will find other uses for those bits fairly quickly if IPv6
takes off.

Marshall Eubanks

> 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

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