4A0-105: Nokia Virtual Private LAN ServicesDemo

By Nokia · Question Mode

QuestionQ124

VPLS loop avoidance

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In the diagram, SAP 1 is placed into the blocking state by the spanning tree protocol. What happens in the VPLS instance if SAP 2 fails and SAP 1 moves to the forwarding state? Select the most accurate statement.

  • A A Spanning Tree BPDU will be sent across the mesh flushing the FDB table in all devices participating in the VPLS instance.
  • B Stale information will be used within the VPLS instance to forward traffic until the FDB ages out.
  • C An LDP control message will be sent to all devices in the mesh participating in the VPLS instance. Only MAC addresses associated with the PE that the failure occurred on will be flushed.
  • D An LDP control message will be sent to all devices in the mesh participating in the VPLS instance. The entire FDB in the VPLS instance will be flushed.
Explanation

An STP topology change is translated into an LDP MAC-address-withdrawal (MAC-flush) message and sent to VPLS peers across the mesh. This broad flush clears learned forwarding information so MAC addresses can be relearned using the newly active SAP, rather than retaining stale FDB entries or flushing only entries tied to the failed PE.

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