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Troubleshooting Virtual Chassis Fabric

This topic describes troubleshooting some common issues for a Virtual Chassis Fabric (VCF):

Large-Scale Virtual Chassis Fabric Becomes Unstable When Logging is Enabled



When detailed system logging or trace operations are enabled in larger-scale VCFs, you observe significant impact on VCF stability, such as:

  • Increased VCF convergence time

  • Traffic interruption


System logging and tracing operations place a load on the primary Routing Engine device in a VCF, taking processing cycles away from managing VCF operations. Logging in general, especially higher levels of logging and tracing operations, can have an impact on VCF stability.


To help ensure good convergence and stable operation in a large-scale VCF, system logging and tracing should always be used with discretion. During normal VCF operation, system logging should be set at or below the notice level, and tracing options disabled. When logging or tracing is necessary to troubleshoot a particular issue, use the following guidelines to minimize impact on VCF stability:

  • Use the detail tracing option or system logging levels at or above the error level only for short periods of time during troubleshooting, and disable these settings after gathering enough information to begin analyzing the issue.

  • Avoid logging the same level of information to more than one log file, which adds extra processing without the benefit of providing more information. Setting up logging to different files for different levels or facilities is a better option.

  • Choose remote logging rather than local logging, and avoid logging to the console.

QFX5100 Leaf Device Assumes Routing Engine Role



A QFX5100 device configured as a leaf device assumes the Routing Engine role during VCF setup. The show virtual-chassis output confirms the role.


The device can assume the Routing Engine role for several minutes during setup before it receives the configuration from the primary Routing Engine, but eventually returns to the linecard role with no user intervention.