Nat

[owen at delong.com (Owen DeLong)]

> On Dec 20, 2015, at 08:57 , Mike Hammett <nanog at ics-il.net> wrote:
> 
> There's nothing that can really be done about it now and I certainly wasn't able to participate when these things were decided. 
> 
> However, keeping back 64 bits for the host was a stupid move from the beginning. We're reserving 64 bits for what's currently a 48 bit number. You can use every single MAC address whereas IPS are lost to subnetting and other such things. I could have seen maybe holding back 56 bits for the host if for some reason we need to replace the current system of MAC addresses at some point before IPv6 is replaced. 

That?s not what happened. What happened was that we added 64 bits to the address space (the original thought was a 64 bit address space) in order to allow for simplified host autoconf based on EUI-64 addresses. It did seem like a good idea at the time.

At the time, IEEE had realized that they were running out of EUI-48 addresses and had decided that the next generation would be EUI-64 and in fact, if you look at newer interfaces (e.g. firewire) you will see that they do, in fact, ship with EUI-64 addresses baked in. Given that IEEE had already decided on EUI-64 as the way forward for ?MAC? addresses, it seems to me that 64 bits makes more sense than 56.

> There may be address space to support it, but is there nimble boundary space for it?

I think you mean nibble-boundary space for it and the answer is yes.

> The idea that there's a possible need for more than 4 bits worth of subnets in a home is simply ludicrous and we have people advocating 16 bits worth of subnets. How does that compare to the entire IPv4 Internet? 

I have more than 16 subnets in my house, so I can cite at least one house with need for more than 4 bits just in a hand-coded network.

Considering the future possibilities for automated topological hierarchies using DHCP-PD with dynamic joining and pruning routers, I think 8 bits is simply not enough to allow for the kind of flexibility we?d like to give to developers, so 16 bits seems like a reasonable compromise.

> There is little that can be done about much of this now, but at least we can label some of these past decisions as ridiculous and hopefully a lesson for next time. 


TL;DR version: Below is a detailed explanation of why giving a /48 to every residence is harmless and just makes sense.

If you find that adequate, stop here. If you are still skeptical, read on?

Except that the decisions weren?t ridiculous. They not only made sense then, but for the most part, if you consider a bigger picture and a wider longer-term view than just what we are experiencing today, they make even more sense.

First, unlike the 100 gallon or 10,000 gallon fuel tank analogy, extra bits added to the address space come at a near zero cost, so adding them if there?s any potential use is what I would classify as a no-brainer. At the time IPv6 was developed, 64-bit processors were beginning to be deployed and there was no expectation that we?d see 128-bit processors. As such, 128 bit addresses were cheap and easily implementable in anticipated hardware and feasible in existing hardware, so 128-bits made a lot of sense from that perspective.