a crude method of limiting long-prefix propagation
Curtis Villamizar
curtis at workhorse.fictitious.org
Mon Mar 26 20:28:58 UTC 2001
In message <4.2.2.20010326124351.00c3c700 at localhost>, "Joel M. Halpern" writes:
> 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 who
> 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
Joel,
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).
Curtis
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