Re: [Idr] draft-walton-bgp-add-paths-06.txt as IDR WG document

Danny McPherson <danny@tcb.net> Tue, 25 November 2008 14:08 UTC

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From: Danny McPherson <danny@tcb.net>
To: PAPADIMITRIOU Dimitri <Dimitri.Papadimitriou@alcatel-lucent.be>
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Date: Tue, 25 Nov 2008 07:08:37 -0700
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Cc: Yakov Rekhter <yakov@juniper.net>, idr@ietf.org
Subject: Re: [Idr] draft-walton-bgp-add-paths-06.txt as IDR WG document
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On Nov 25, 2008, at 6:13 AM, PAPADIMITRIOU Dimitri wrote:
>
> if an id is prepended to the best path, and only the latter is
> advertized this would not incur more instability than today's  
> situation.
> except if for whatever reason the BGP speaker decides to modify that  
> id
> (if my reading is correct nothing prevent this from the current
> write-up)
>
> when multiple paths (each prepended with an id) are progressively
> advertized you have an effect on and then each would be progressively
> removed (A:ID1, A:ID2,..., A:IDn) and then (W:ID1, W:ID2,...,W:IDn)
> compared to the current situation where after the initial  
> advertisement,
> a sequence of increasing length path is advertized followed by a
> withdrawal or stabilization to a newly preferred path. So the effect  
> is
> the delta on the withdrawn sequence from W:ID1,...,W:IDi (in the work
> case, i=n i.e. the full sequence is withdrawn) and the delta on the
> advertized sequence A:IDj,...,A:IDn (in the worst case j=2 i.e. one
> would stabilize on the second path)

I mean between adjacent nodes, not system wide.  More paths
means more state, more paths means more churn.  This is the
obvious trade-off here when employing add-path.

-danny

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