We present a novel proactive routing algorithm that continuously searches f
or failures via frequent ICMP echo requests, Our approach differs from its
predecessors in that it is proactive instead of reactive. That is, we conti
nuously;search for failures before they affect message transmissions. When
a failure is detected, an alternative route is identified and used. The Dyn
amic Routing System (DRS) is currently deployed commercially by one of the
top-three United States telecommunications companies in over 27 major citie
s nationwide. In production use, the use of DRS has improved availability b
y 13%. (C) 1999 Elsevier Science B.V. All rights reserved.