QuestionQ26

Network Design

In a redundant hub-and-spoke “wheel” topology, every spoke is connected to the hub, and spokes also connect to other spokes. If one spoke link fails, traffic from that site can be sent to a neighboring site, which forwards it to the hub site. However, at peak hours, an overloaded link causes traffic to be rerouted to a neighbor that then becomes overloaded. This overload produces network-traffic oscillation as the load changes at each spoke site. The design supplies more redundancy but not more resiliency because the routing protocol must evaluate many alternate paths to identify the lowest-cost path.

Which two design changes help improve resiliency in this situation?

Choose two
  • A Increase the number of redundant paths considered during the routing convergence calculation.
  • B Eliminate links between every spoke.
  • C Increase routing protocol convergence timers.
  • D Increase unequal-cost parallel paths.
  • E Use two links to each remote site instead of one.
Explanation

Resiliency improves when remote sites have redundant direct connectivity to the hub while spokes are prevented from becoming transit routers for one another. Eliminating inter-spoke links removes the large set of alternate transit paths that drives oscillation and routing complexity. Providing two links to each remote site preserves link-failure protection through direct parallel paths, avoiding dependence on a neighboring spoke. Cisco design guidance identifies redundant parallel paths as a basis for resiliency and recommends simplifying multiple physical paths into a logical bundled interface.

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