North American Network Operators Group

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Re: IPv6 routing /48s

  • From: Michael Sinatra
  • Date: Mon Nov 17 18:22:20 2008

On 11/17/08 14:46, [email protected] wrote:

ARIN claims they are seeing /48s routed, at least in their route tables. I have seen some new momentum on the allocation of /32's, don't know if that is in response to rules like this?? Would be awefully difficult for our organization to come up with the rationale to need 65K /48s internally to justify a /32.

You may want to post this issue to the ARIN PPML list (see if you're not already subscribed), as that might be a useful venue for discussion as well.

You're right in noting that this is a catch-22. ARIN and other RIRs are now giving out PI /48s, but there is still a notion that /32 is considered the maximum routable prefix length. However, UCB sees a lot of globally-routed /48s (and /35s, /40s, etc.) in our DFZ routing table. (I also see some /48s disaggregated from a /32 and announced in at least one non-ARIN region, but I am sure this is happening elsewhere. :-( ) So, I do think that /48 is beginning to be the new /32 when it comes to prefix filtering, but I can also understand those who want to hold to the more strict IPv6 filtering policies.

I think in the end, we are going to end up generally accepting up to /48s. Basically, we're going to break the routing table anyway--the number of potential /32s is more than enough to do that, and forcing everyone who:

a. needs to be multi-homed; and
b. needs more than 1-2 subnets

to get a /32 has to be a waste, no matter how big the potential address space is overall.

One compromise would be to require that blocks that can be aggregated be aggregated, and then allow PI /48s. In theory, this could be enforced a number of ways, but I am sure we're all aware of how well that works...