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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