Troubleshoot common router, operation problems

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Questions derived from the 642-425 – IP Telephony Troubleshooting Exam Cisco Self-Test Software Practice Test.


Objective: Troubleshoot common router, switch and gateway configuration, integration and operation issues and problems
SubObjective: Determine the effect of Layer 2 configuration errors on an IPT network operation


Item Number: 642-425.4.1.12
Single Answer, Multiple Choice


A Cisco IP phone appears to reset only when there is heavy FTP download or SAP application access on computers that connect to the same switch as the IP phone. Which of the following is the most likely cause of the problem?



  1. There is an IP address conflict.
  2. The voice VLAN is not added to VLAN database.
  3. The Cisco IP phone does not have voice VLAN configured.
  4. The Cisco IP phone lost connectivity to the CallManager.
  5. The DHCP lease for the Cisco IP phone IP address expired.


C. The Cisco IP phone does not have voice VLAN configured.


The most likely reason for IP phone resetting is that the Cisco IP phone does not have voice VLAN configured. As the IP phone supports the connection to the PC, the Ethernet link that connects to an IP phone can carry both voice and data traffic. Because voice traffic is delay sensitive, it should be sent on a separate voice VLAN with necessary QoS implemented. This is required because QoS parameters for data traffic differ from real-time traffic such as voice and video.


In this scenario, if voice VLAN is not configured, and IP phone operates via regular VLAN, heavy data traffic activity could interfere with the delay-sensitive voice traffic causing the IP phone to loose connectivity with Cisco CallManager and reset.


If Voice VLAN is not added to the VLAN database, there will be no communication; therefore, this is not a correct option.


All other options can be valid reasons for IP phone resetting. But they are not related to the specific condition of IP phone resetting only under heavy network transaction as in this scenario.



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