Discuss redundant switch supervisors.
What are the redundancy modes?
bigger switches have 2 supervisor modules. the secondary one can be in a state of readiness to take over.
RPR (Route processor redundancy) - only partially booted up, upon main failure must reload all switch modules and take over.
RPR+ (Route processor redundancy Plus) - is booted up, up to route engine initialization. No L2 or L3 functions are started. Upon failure, all switch modules don't have to reload.
SSO (Stateful Switchover) - Secondary supervisor is fully booted and running all functions up to L3, ( L2 FIB table is synchronized).
Note: NSF (Non Stop Forwarding) takes SSO a step further, and makes rebuilding of the FIB faster using other NSF aware neighbors. (aka, it does not have to wait for L3 routing protocols to fully converge)