In Cisco Nexus switches, when transitioning from a single supervisor module to a dual supervisor

configuration, the behavior depends on the redundancy mode configured.​

Stateful Switchover (SSO): In configurations supporting SSO, the active and standby supervisors

synchronize their state and configuration, allowing for seamless failover without resetting other

modules.​

Stateless Switchover (Warm Standby): In certain modes, such as the ACI-mode on Cisco Nexus 9508

switches, the standby supervisor does not maintain synchronized state information with the active

supervisor. In this scenario, if a switchover occurs (e.g., due to the replacement of the active

supervisor), all modules in the switch are reset because the switchover is stateless.​

Therefore, when a supervisor module is replaced in a configuration that does not support stateful

switchover, all modules in the switch are reset due to the stateless nature of the switchover.​

Reference: Supporting Cisco Devices for Field Technicians (FLDTEC) – Maintenance and RMA

Procedures​

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