Keeping in reserve, was: Re: [address-policy-wg] Provider Independent (PI) IPv6 Assignments for End User Organisations (2006-01)

On 28-sep-2006, at 14:35, JORDI PALET MARTINEZ wrote:

> One possibility will be to allocate /48 but keep reserved the  
> remaining /32.
> If the applicant justify that the /48 is getting filtered, then he  
> may opt
> to justify to obtain the /32. Is this a possible compromise solution ?

History, both in IPv4 and IPv6, has shown that keeping space in  
reserve to accommodate future request doesn't work very well: people  
often end up announcing several blocks anyway. So let's not waste the  
space and make filtering harder by doing this. Also, since a /48 is  
an incredible amount of space to begin with, coming back for more  
should be rare in IPv6.

The advantage of only giving out /48s with no unused space between  
them is that if, for instance, 12000 /48s are given out, that will be  
from a single /34 and allowing /48s from a /34 allows 16384 routes,  
while allowing /48s from a /20 (because for every /48 of 12000 a /32  
is kept in reserve) allows 268 million routes, more than enough to  
overload any reasonable routing system in an attack.