IPv6 Default Allocation - What size allocation for Loopback Address

Sun Oct 12 22:44:17 UTC 2014

On 10/12/14 3:00 PM, William Herrin wrote:
> On Sat, Oct 11, 2014 at 1:41 AM, Faisal Imtiaz <faisal at snappytelecom.net> wrote:
>> A follow up question on this topic..
>>
>> For Router Loopback Address .... what is wisdom in allocating a /64 vs /128 ?
>> (the BCOP document suggests this, but does not offer any explanation or merits of one over the other).
> 
> Hi Faisal,
> 
> One of the viewpoints held by some in the IETF is that an IPv6 address
> is not 128 bits. Rather, it is 64 bits of network space and 64 bits of
> host space. I'm told this viewpoint is responsible for the existence
> of a 128 bit address instead of IPv6 using 64 bit addresses.
> 
> If you follow that reasoning, the subnet mask should always be /64, no
> matter where the address is assigned.

https://tools.ietf.org/html/rfc6164

Is a standards track document.

it is imho a repudiation of the assumptions about the dimensions of the
host field.

> There are, of course, excellent operational reasons not to religiously
> follow that plan.
> 
> Regards,
> Bill Herrin
> 
> 
> 

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