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Re: What is the limit? (was RE: multi-homing fixes)

  • From: George Michaelson
  • Date: Wed Aug 29 20:52:30 2001

> | If you had a router that could handle 2^32 prefixes, it will handle
> | the IPv4 Internet.  Forever.  The whole growth curve argument is
> | gone.
> Sure, just about anybody can build a router which has 2**32 forwarding
> directives burned into ROM.  It gets easier with fewer interfaces, too.
> But, who wants a static network?

I do. and probably 99% of the userbase like me. Because, when *we*
say static, we mean different to when you say static. Humpty Dumpty rules.

Really, nobody wants dynamic routing. They just pretend its a feature, but
given the amazingly static nature of cables in the ground and edge devices
Kansas miraculously stays in the mid-west, I say in Brisbane mostly and
what I want is a static declaration in the routing model of the world that
says Brisbane is not in Kansas. And, based on what I hear from smarter people
that is what BGP says. How much of the updates you see actually change
anything about which of your links packets flow on? I bet its marginal
change, not earth shattering change mostly. I mean, do you *WANT* to
live on the edge of mt etna, or would you rather look at it from a
stable place?

Dynamic updates are chicken little. "THEY SKY IS FALLING! I CAN'T SEE <x>"
followed 1/2 an hour later by "oh, yes I can" Better to say nothing to the
world, and tell your next door friend who isn't under the cardboard sheet
so they can help lift it for you. If you want dynamicism, do it locally please.

> In the early 90s we had a network where you could wait a week
> before the core of the Internet adapted to your topology change,
> and changed its routing towards a particular prefix.  It wasn't
> really much fun.

And guess what? Now we have a network where it can take two weeks to
make an upstream edit their hand-crafted BGP and nothing has changed.

Your point was?

> And neither can the rate of change.  The problem only has to be Too Hard
> to compute affordably, not NP-complete.

This is like a mathematical version of Godwins law. But, there would appear
to be people who assert its not unafordable to compute the routes for
the current, and the forseeable network. so its neither NP complete nor
unaffordable. Its also irrelevant because it looks like prefix collapse
on the global /24 or /32 table is workable for most% of the world forever
in internet terms. Saying CiDR makes BIFF admit the NETWORK FAILED is well,
like BIFF. Just because its set in capitals, doesn't make it TRUE!

> | "it's exponential and we'll never get ahead of it" is crap.  It
> | won't be forever, so let's get ahead of it.
> There's lots of irony in that too.   Other than the hand-wave,
> how do you propose to get (and stay) ahead of it?
> 	Sean.

By filtering the /24's which when removed, drop > 1% < 20% of the
routing table size (I invented those numbers) but lose >30% (I invented
that one too) of the dynamicicsm of silly/pointless route annoucements,
and appear to cause (after the two weeks of finding all the CNN like
agencies on /24) a markedly marginal loss of connectivity for most% of the
network. As if you also don't expect this to (a) work, and (b) continue
to make previously believed exponential growth become more linear.

Market forces also help. dotcom crash == merger & acquisitions == longterm
baseline no questions asked handback for aggregation == less demand
for new nets == less rate of growth of prefixes. rate of growth is measured
in months and years. BGP updates are in tens of seconds. the relationships
are not exactly 1:1 ratio are they?

Its coming. Rant as much as you like, filtering is back on the agenda.
And, I am willing to suggest once the brouhaha settles down, we all find
it suprisingly pleasant afterwards.

NOPEER is probably as relevant, because the /24 issue is about a more
local horizon of announcement. As Geoff Huston says, NOPEER flies as
far as your money. Randys /24 filters meet it at that point, and we all

Mind you, those two weeks of CNN suing everyone in sight is going to be fun!

My hope is this makes everyones mailfilters. I mentioned Godwins law so it
should do.