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

Stephen Sprunk stephen at sprunk.org
Thu Sep 14 00:39:57 CEST 2006

Thus spake "Jeroen Massar" <jeroen at unfix.org>
> 8<-----------------------------------------
> IPv6 Assignment Blocks   CIDR Block
> 2620:0000:/23
> ----------------------------------------->8
> 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 

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