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Re: IPv6 PI block is announced - update your filters 2620:0000::/23

  • From: Stephen Sprunk
  • Date: Wed Sep 13 19:14:43 2006

Thus spake "Jeroen Massar" <[email protected]>
IPv6 Assignment Blocks   CIDR Block
Expect blocks in between /40 and /48 there.
Expect mostly /48s and /44s, given that ARIN has not defined any criteria for what justifies more than a /48. Of course, some folks will announce a /44 instead since the block is reserved, but it should still only be one route.

Still, even if every org that qualified for an assignment today got one, you're still only looking at a couple tens of thousands of routes max. ARIN using a /23 for PIv6 is either serious overkill or "we'll never need to allocate another block" at work.

That is enough space for best-case 2^(40-23) = 131.072 routes, worst
case 2^(48-23) = 33.554.432 extra routes in your routing table, I hope
Vendor C can handle it by the time that happens. In order words: better
start saving up those bonus points, you will be buying quite a lot of
new gear if this ever comes off the ground ;)

Most likely case is a bit more optimistic if one takes /44's: 2.097.152
Still a lot more than the IPv4 routing table is now. It will take time,
and possibly a lot, but it could just happen...
IMHO, BGP will fall over and die long before we get to that many ASNs. Remember, the goal in giving people really big v6 blocks, vs. IPv4-style multiple allocations/assignments, is to reduce the necessary number of routes to (roughly) the number of ASNs.

If PIv6 folks start announcing absurd numbers of routes within their allocation, I'd expect ISPs to start filtering everything longer than /48 -- if they don't do so from the start. The next step is to filter everything longer than /44; since everyone is getting a reserved /44 at a minimum, that's safe (everyone just announces the /44 in addition to more-specifics). If filtering at /44 isn't enough, ISPs will just drop all PIv6 routes except for their customers' and the concept dies a quick death. No routers will be harmed in the making of this movie.

It just occured to me that this policy is a perfect counterexample to Kremen's claims that ARIN is run by big ISPs for their own benefit. The big ISPs wailed and moaned and tried to stop it, and history may even prove them right one day, but the little guys won for now. Even if we're wrong, that's a good thing for a variety of reasons.


Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking