The stable paths problem and interdomain routing

  • Griffin T
  • Shepherd F
  • Wilfong G
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Dynamic routing protocols such as RIP and OSPF essentially
implement distributed algorithms for solving the shortest paths problem.
The border gateway protocol (BGP) is currently the only interdomain
routing protocol deployed in the Internet. BGP does not solve a shortest
paths problem since any interdomain protocol is required to allow
policy-based metrics to override distance-based metrics and enable
autonomous systems to independently define their routing policies with
little or no global coordination. It is then natural to ask if BGP can
be viewed as a distributed algorithm for solving some fundamental
problem. We introduce the stable paths problem and show that BGP can be
viewed as a distributed algorithm for solving this problem. Unlike a
shortest path tree, such a solution does not represent a global optimum,
but rather an equilibrium point in which each node is assigned its local
optimum. We study the stable paths problem using a derived structure
called a dispute wheel, representing conflicting routing policies at
various nodes. We show that if no dispute wheel can be constructed, then
there exists a unique solution for the stable paths problem. We define
the simple path vector protocol (SPVP), a distributed algorithm for
solving the stable paths problem. SPVP is intended to capture the
dynamic behavior of BGP at an abstract level. If SPVP converges, then
the resulting state corresponds to a stable paths solution. If there is
no solution, then SPVP always diverges. In fact, SPVP can even diverge
when a solution exists. We show that SPVP will converge to the unique
solution of an instance of the stable paths problem if no dispute wheel

Author-supplied keywords

  • BGP
  • Border gateway protocol
  • Interdomain routing
  • Internet routing
  • Path vector protocols
  • Stable routing

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  • Timothy G. Griffin

  • F. Bruce Shepherd

  • Gordon Wilfong

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