North American Network Operators Group
Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: shim6 @ NANOG (forwarded note from John Payne)

  • From: Iljitsch van Beijnum
  • Date: Thu Mar 02 10:52:55 2006 
On 2-mrt-2006, at 16:20, Mark Newton wrote:


Now, some may take that as a sign the IETF needs to figure out how
to handle 10^6 BGP prefixes...  I'm not sure we'll be there for a
few years with IPv6, but sooner or later we will, and someone needs
to figure out what the Internet is going to look like at that point.



It won't look good. ISPs will have to buy much more expensive
routers. At some point, people will start to filter out routes that
they feel they can live without and universal reachability will be a
thing of the past.





But don't we filter out routes we feel we can live without *right now*
without the world ending?




Did I say that the world would end? All of this is important stuff
but fortunately not THAT important...




I mean, who accepts prefixes longer than /24 these days anyway?
We've all decided that we "can live without" any network smaller
than 254 hosts and it hasn't made a lick of difference to
universal reachability.




...because everyone who can't get a /24 will find another way to
connect to the internet. Now suppose that today we all filter at /24
but tomorrow we start...




What's to stop someone who wants to carry around less prefixes from
saying, "Bugg'rit, I'm not going to accept anything smaller than
a /18"?




This will break connectivity to MANY parts of the internet. And yes,
you can do this if you want. Your customers may not like the new
policy, though. A more realistic scenario would be to go from /24 to /
23, which will make your routing tables a lot smaller but not break
_too_ much. If enough people start doing this, people who have a /24
will have to renumber into a larger block or move to PA space. And
two years later it's /22 and so on. At this point, the people at the
short end of that stick may start to think that shim6 wasn't so bad
after all.



Note that in IPv6 all of this will play out differently because you
basically have /32s for most ISPs (some shorter ones as well of
course, but no longer ones for ISPs) So filtering on prefix length
(other than as a safety mechanism against accidental deaggregation)
won't be useful. Today you can deaggregate a /16 into 256 /24s, but
deaggregating a /32 into 65536 /48s is of course more problematic.



But maybe in IPv6 people will filter out stuff from other regional
registries. Especially when they discover multihoming in Asia.