IPv6 Subnet tool

[Joe Abley]

On 14 Jan 2009, at 14:06, David Conrad wrote:

> On Jan 14, 2009, at 8:47 AM, Joe Abley wrote:
>> People whose habit it is to assign /56s seem like they are most  
>> likely to cause annoyance to customers who are migrating from some  
>> other provider who gave them (reasonably) a /48.
>
> Not sure what the annoyance would be: going from a /56 to a /48  
> doesn't require any more renumbering than going from one /48 to a  
> different /48.  Where the annoyance comes in is going from a /48 to  
> a /56...

Moving from a /56 to a /48 is easy; the annoyance is in the other  
direction. If your numbering scheme for your assigned /48 is of the form

   xxxx:xxxx:xxxx:SUBNET:<64-bit-EUI>

(i.e. you're identifying individual /64 prefixes using some 16-bit  
integer denoted as SUBNET above), that doesn't map nicely into a /56  
unless you make the conscious decision not to use the top eight bits  
of the SUBNET value (in which case you've really only got a /56).

I'm not saying it's a huge deal, but in general it seems like it is  
non-zero work. This seems like a shame for an address format that was  
chosen, in part, to make renumbering easier.


Joe