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400-007 · Question #129

400-007 Question #129: Real Exam Question with Answer & Explanation

The correct answer is C: CPU usage on the hub router. IP SLA responders process all incoming probe packets in software on the hub router, so monitoring CPU usage on the hub is critical as spoke site count grows.

Question

Company XYZ has a hub-and-spoke topology over an SP-managed infrastructure. To measure traffic performance metrics, they implemented IP SLA senders on all spoke CE routers and an IP SLA responder on the hub CE router. What must they monitor to have visibility on the potential performance impact due to the constantly increasing number of spoke sites?

Options

  • ACPU and memory usage on the spoke routers
  • Bmemory usage on the hub router
  • CCPU usage on the hub router
  • Dinterface buffers on the hub and spoke routers

Explanation

IP SLA responders process all incoming probe packets in software on the hub router, so monitoring CPU usage on the hub is critical as spoke site count grows.

Common mistakes.

  • A. Each spoke router generates only its own IP SLA probes regardless of total spoke count, so spoke CPU and memory do not scale with the growing number of sites.
  • B. IP SLA responder operations are CPU-bound rather than memory-bound, so memory consumption on the hub does not increase significantly as more spoke sites send probes.
  • D. Interface buffer utilization relates to traffic queuing and congestion, not to the software processing overhead introduced by IP SLA responder operations.

Concept tested. IP SLA responder CPU scalability in hub-and-spoke

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipsla/configuration/xe-16/sla-xe-16-book/sla_overview.html

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