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 < 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 
> 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
>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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