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Re: The Cidr Report

  • From: Warren Kumari, Ph.D, CCIE# 9190
  • Date: Sun Feb 13 10:20:13 2005

Hash: SHA1

On Feb 13, 2005, at 2:31 AM, Christopher L. Morrow wrote:

On Sat, 12 Feb 2005, Alexander Koch wrote:

On Sat, 12 February 2005 14:58:42 +0000, Stephen J. Wilcox wrote:
From: "Stephen J. Wilcox" <[email protected]>
[...] - would you agree that most of the poor deaggregating is not intentional
ie that they're announcing their '16 class Cs' or historically had 2 /21s and
Think about someone putting in a Null0 route and re-
exporting stuff unconditionally, now after he originates
his /19 he is then adding a /24 here, and a /25 there.
Lack of experience, when you suggest to them they should
remove these announcements they are afraid to change it,
not understanding the implications, etc.

Not to mention ppl using cisco and prefix lists, it is
way too easy with cisco to say '/19 le 24', and then they
use outbound prefix lists to their transit supplier
(different, but related as I see it). Some transit ISPs
use that a lot, and encourage the table growth.
There are some business reasons to de-aggregate. Look at some outages
caused by 'routing problems' (someone leaked my /24's to their peers,
peers, peer and my traffic got blackholed, because the public net only
knows me as a /20)

There are multiple reasons for deaggregation aside from 'dumb operator',
some are even 'valid' if you look at them from the protection standpoint.

That and the "I have 1 circuit to $good_provider and 1 circuit to $bad_provider and the only way I can make them balance is to split my space in half and announce more specifics out through each provider" argument. I have also often seen people do this without announcing the aggregate because <some undefined bad thing> will happen, usually justified with much hand-waving. The people who do this can usually not be reasoned with....

It happens all the time...


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