Migration failed : illegal network configuration: cluster subnet 100.64.0.0/14; overlaps built-in join subnet 100.64.0.0/16 in OpenShift Container Platform 4

Solution Verified - Updated -

Issue

  • While migrating OpenShift 4.6 from OpenShiftSDN to OVN-Kubernetes, migration failed with an error:

    Migration failed : illegal network configuration: cluster subnet "100.64.0.0/14" overlaps built-in join subnet "100.64.0.0/16"
    
  • How to change the OVN-Kubernetes internal join range of 100.64.0.0/16 if that is overlapping and already in use on the OCP cluster?

  • Migration from OpenShiftSDN to OVN-Kubernetes is blocked because the join subnet of OVN-Kubernetes can not be changed.

Environment

  • Red Hat OpenShift Container Platform (RHOCP) until 4.12
  • OpenShiftSDN to OVN-Kuberntes migration

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