Route Flap Damping: Harmful ?

["Christian Panigl, ACOnet/VIX/UniVie" <]

    Dear RIPE Routing-WG members,
    
    at the RIPE43 meeting in Rhodes last week Randy Bush was giving an
    interesting presentation on recent observations of counterproductive
    effects of current implementations of BGP Route Flap Damp(en)ing.
    
    The presentation is available in Acrobat Reader format at:
    
http://www.ripe.net/ripe/meetings/archive/ripe-43/presentations/ripe43-routing-flap.pdf

    Brief summary:
    
    Basically because of "Cascaded Withdrawals" a single original flap of a
    prefix may cause the route flap penalty to exceed the suppress threshold
    at some points (routers) in the Internet.  Main reasons for this
    behaviour are the characteristics of BGP (path vector), variations in
    BGP timers and delays, algorythm, implementation and parameters of
    current Route Flap Damping.
    
    This phenomenon is also (though less clearly) described in RIPE-229
    (Flap Damping Parameter Recommendation), as it was in its predecessors
    since early 1998:
    
http://www.ripe.net/ripe/docs/ripe-229.html#4.1

    Only in late July this year I did again observe severe occurences of
    this phenomenon and was starting a conversation with Philip Smith
    (Cisco) and others.
    
    Now there is a SIGCOM 2002 Publication (August 2002)
    "Route Flap Damping Exacerbates Internet Routing Convergence"
    by Z.Mao and others:
    
http://www.cs.berkeley.edu/~zmao/Papers/sig02.pdf

    I would like to thank the authors for the excellent research and, as one
    of the authors of RIPE-229 and its predecessors, I'm acknowledging that
    we haven't yet been able to analyse this specific problem in detail, but
    have communicated it to e.g. the MERIT/IPMA project team.
    
    I'm therefore more than grateful that Z.Mao and his co-authors did
    finally investigate it and would like to propose to the RIPE Routing-WG
    that we formally acknowledge their work, and specifically support their
    conclusion.
    
    Comments are of course welcome !
    
    Kind regards
    CP
    
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