consistent policy != consistent announcements

Tony Li tli at
Mon Mar 17 06:58:48 UTC 1997

   2) generally speaking, BGP path length is too blunt an instrument.  More
   fine-grained control is needed to allow peers to fine-tune balance of
   their interests.  I'm sorry to be too naive, but i'm repeating that for
   years and nobody seems to agree that BGP needs real metrics.  How come? 

Well, for several reasons.

First, any such proposal should have a reasonable architecture.  Not just a
description of the mechanism.  Motivational explanations are most welcome,
preferably sprinkled with real world examples.

Second, there's the issue of the consistency of the values used.  As I
recall your proposal, each domain in the path would propose a metric for
its contribution for a prefix.  A receiving domain then weighted each
domain in whichever way it chose to arrive at a final, composite metric.
Thus, the semantics of the metric are hardly clear.

Third, there's the pragmatic issue of implementation cost.  Yes, the cost
of an integer per AS in an AS path is tolerable, tho not "cheap".  This
cost becomes painful if most domains are not using the metric.  And it
becomes more painful if two prefixes with otherwise identical attributes
have different metrics.  This results in them not landing in the same
update, thereby increasing overhead.  Are we willing to take a signficant
step forward in overhead for this flexibility?  


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