[ppml] Fwd: Keeping in reserve
> -------Original Message-------
> From: Kevin Loch <kloch at kl.net>
> Subject: Re: [ppml] Fwd: Keeping in reserve
> Sent: 05 Oct '06 13:11
> Iljitsch van Beijnum wrote:
> > So what is the downside of simply giving out an additional, non-
> > growable prefix when a /48 isn't enough?
> This results in involuntary fragmentation just like slow-start
> in IPv4.
> > Or just give out the space that would have been reserved immediately,
> > i.e., give out /44s instead of /48s?
> That provides more space with which to voluntarily deaggregate. That
> could be a feature or a problem depending on your perspective. It could
> also be seen as unnecessarily wasteful since /48 is already a very
> generous minimum assignment.
> I like the bisection method. It provides the maximum ability to expand
> delegations without fragmentation. It also removes any perceived
> relationship between reserved space and your delegation.
In general, bisection seems like a good strategy. The problem with bisection from my perspective is what happens when the super-block you are assigning from becomes close to "full."
In this case ARIN has decided to assign IPv6 PI from the block 2620:0000:/23 (http://www.arin.net/reference/ip_blocks.html).
Because of the IPv6 policy agreed to between IANA & the RIRs. ARIN can't go back and get more IPv6 address space until they have assigned/allocated/reserved 50% of the space they have been given. At least that is how I read the policy. (http://www.icann.org/policies/proposed-ipv6-policy-14jul06.htm)
If you are assigning /48s without reservations then you force bisection down to the /47 level. If any org wants to grow bigger than a /47 then you force fragmentation by not having a reserve. The IPv6 policy between the RIRs & IANA recognizes reserved address space as "unavailable" for the purposes for obtaining additional address resources from IANA.
The reserve method isn't perfect, but I believe it is reasonable based upon what we know now.