a crude method of limiting long-prefix propagation
Joel M. Halpern
joel at longsys.com
Mon Mar 26 20:55:55 UTC 2001
Fair enough. Given the potential size of the list, I wanted to make sure
we thought about the alternative. Having thought about it, we can
certainly conclude (as Curtis has) that instead we can treat a long list as
a warning sign that someone is doing something that probably causes problems.
At 03:28 PM 3/26/01 -0500, Curtis Villamizar wrote:
>In message <18.104.22.16810326124351.00c3c700 at localhost>, "Joel M. Halpern"
> > Using Exclude is better under certain topological conditions.
> > The primary condition is when the point where the disparate paths are
> > exquivalent (in an AS sense) is such taht a reasonably large number of AS
> > need the multiple advertisements
> > and
> > where topologically there are a relatively small number of boundary AS
> > only need the aggregation, and will take of further distribution of the
> > aggregated information.
> > The purpose is to have an alternative mechanism to limit how many AS one
> > must include in the distribution list. You or Yakov are probably in a
> > better position than I to see if the topology would actually make it
> > useful. It just seems that some knob for the more remote case might well
> > be helpful. [Remote of course has nothing to do with geography. In some
> > metros, there are be several AS between facilities two blocks apart.]
> > Yours,
> > Joel M. Halpern
>There are thousands of AS allocated and in use. Most leaks through
>aggregates need only be advertised to a few AS. The "include list"
>will be much shorter than an "exclude list". It is also better to
>require that the more specific be leaked to a well thought out set of
>AS where there is a known purpose for having the more specifics leaked
>(ie: a reason such as it is needed for local load balancing).
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