minimum IPv6 announcement size

William Herrin bill at
Fri Sep 27 18:11:02 UTC 2013

On Fri, Sep 27, 2013 at 1:04 PM, Randy Carpenter <rcarpen at> wrote:
>> There is no bit length which allocations of /20's and larger won't
>> quickly exhaust. It's not about the number of bits, it's about how we
>> choose to use them.
> True, but how many orgs do we expect to fall into that category? If the majority are getting /32, and only a handful are getting /24 or larger, can we assume that the average is going to be ~/28 ? If that is so, then out of the current /3, we can support over 30,000,000 entities. Actually, I would think the average is much closer to /32, since there are several orders of magnitude more orgs with /32 than /20 or smaller. Assuming /32 would be 500 million out of the /3. So somewhere between 30 and 500 million orgs.
> How many ISPs do we expect to be able to support? Also, consider that there are 7 more /3s that could be allocated in the future.

Hi Randy,

If that's how we choose to use IPv6 then runout should be a long way
away. That's a big "if". And choosing to stay that course is a form of

> Therefore, I don't see any reason to artificially inflate
> the routing table by conserving, and then making
> orgs come back for additional allocations.

I'm not convinced of that. Suppose the plan was: you start with a /56.
When you need more you get a /48. Next is a /40. Next a /32. Next a
/28. You can hold exactly one of each size, never more. And the RIRs
tell us all which address banks each size comes from.

In such a scenario, the RIR doesn't have to reserve a /28 for
expansion every time the allocate a /32. 'Cause, you know, that's what
they've been doing. And you can easily program your router to discard
the TE routes you don't wish to carry since you know what the
allocation size was. That means you only have to carry at most 5
routes for any given organization. You'd want to allow some TE for the
sake of efficient routing, but you get to choose how much.

As things stand now, you're going to allow those guys with the /19s
and /22s to do traffic engineering all the way down to /48. You don't
have a practical way to say "no."

Food for thought.

Bill Herrin

William D. Herrin ................ herrin at  bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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