Mike Hammett nanog at
Sun Dec 20 16:57:49 UTC 2015

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. 

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

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? 

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. 

Mike Hammett 
Intelligent Computing Solutions 

----- Original Message -----

From: "Daniel Corbe" <corbe at> 
To: "Mike Hammett" <nanog at> 
Cc: "Mark Andrews" <marka at>, "North American Network Operators' Group" <nanog at> 
Sent: Saturday, December 19, 2015 10:55:03 AM 
Subject: Re: Nat 


> On Dec 19, 2015, at 11:41 AM, Mike Hammett <nanog at> wrote: 
> "A single /64 has never been enough and it is time to grind that 
> myth into the ground. ISP's that say a single /64 is enough are 
> clueless." 
> A 100 gallon fuel tank is fine for most forms of transportation most people think of. For some reason we built IPv6 like a fighter jet requiring everyone have 10,000 gallon fuel tanks... for what purpose remains to be seen, if ever. 

You’re being deliberately flippant. 

There are technical reasons why a single /64 is not enough for an end user. A lot of it has to do with the way auto configuration works. The lower 64 bits of the IP address are essentially host entropy. EUI-64 (for example) is a 64 bit number derived from the mac address of the NIC. 

The requirement for the host portion of the address to be 64 bits long isn’t likely to change. Which means a /64 is the smallest possible prefix that can be assigned to an end user and it limits said end user to a single subnet. 

Handing out a /56 or a /48 allows the customer premise equipment to have multiple networks behind it. It’s a good practice and there’s certainly enough address space available to support it. 

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