Renumbering for better aggregation (was Re: too many routes)

J.D. Falk jdfalk at
Tue Sep 9 18:12:52 UTC 1997

On Sep 9, Phil Howard <phil at> wrote: 

> In general, is it better to have you IP space scattered amongst a lot of
> different /24's /25's and /26's or would it be better to collect everything
> into a large /19 or /18, when going to BGP4?
> I would think the latter.  If so, would anyone know why it is that the
> backbone providers are so resistant to giving out blocks to do this?
> Could it be because they won't be able to do anything with the small
> pieces that get returned and those will end up going to waste because
> they are so fragmented?  Or perhaps they don't even have procedures in
> place to do anything with returned address space, yet?

	Okay, this is somewhat operational (more policy, but it's
	something backbone operators need to think about) -- how
	many of y'all actually /do/ have a policy in place for
	when your downstream customers want to reaggregate?  For
	that matter, how many of you have had to think about it
	before?  (I'm not looking for a show of hands, of course,
	just some interesting discussion.)

	Personally, I dealt with that somewhat in a previous job,
	where we were returning space originally allocated to us 
	by Net99 (yup, it's a common story), and therefore forcing 
	just about all of our long-time customers to renumber.  It 
	was not fun, but I tried real hard to make it go well.

	So, I figured out which of our customers were in a good
	position to be renumbered into a better aggregate block as
	long as they were going to have to renumber anyway, and
	assigned new addresses accordingly.

	The main failing in the plan was that I got assigned to a
	different project before the renumbering was completed.

	My guess would be that it'd be a little more difficult if
	you or your customer were trying to reaggregate without the
	impetus that your existing addresses didn't have valid 
	reverse DNS any more, and were gonna be forcibly reclaimed
	in a few months.

J.D. Falk                         voice: +1-415-482-2840 	
Supervisor, Network Operations      fax: +1-415-482-2844

"The People You Know.  The People You Trust."

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