Route Flap Damping
Exacerbates Internet Routing Convergence.
Zhuoqing Morley Mao (UC abstract: Route flap damping is considered to be a widely deployed
mechanism in core routers that limits the widespread propagation of unstable
BGP routing information. Originally
designed to suppress route changes caused by link flaps, flap damping
attempts to distinguish persistently unstable routes from routes that
occasionally fail. It is considered to
be a major contributor to the stability of the Internet routing system. We show in this paper that, surprisingly,
route flap damping can significantly exacerbate the convergence times of
relatively stable routes. For example,
a route to a prefix that is withdrawn exactly once and re-announced can be
suppressed for up to an hour (using the current RIPE recommended damping
parameters). We show that such abnormal behavior fundamentally arises
from the interaction of flap damping with BGP path exploration during route
withdrawal. We study this interaction
using a simple analytical model and understand the impact of various BGP
parameters on its occurrence using simulations. Finally, we outline a preliminary proposal
to modify route flap damping scheme that removes the undesired interaction in
all the topologies we studied. Papers are provided as
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paper is available in Adobe PDF format. |