58 Switch FeaturesMaster Failover with Transparent TransitionThe stacking feature supports astandby or backup unit that assumes thestack master role if the stack master fails. As soon as a stack master failure isdetected, the standby unit initializes the control plane and enables all otherstack units with the current configuration. The standby unit maintains asynchronized copy of the running configuration for the stack.Nonstop Forwarding on the StackThe Nonstop Forwarding (NSF) feature allows the forwarding plane of stackunits to continue to forward packets while the control and managementplanes restart as a result of a power failure, hardware failure, or software faulton the stack master and allows the standby switch to quickly takeover as themaster.Hot Add/Delete and Firmware SynchronizationYou can add and remove units to and from the stack without cycling thepower. When you add a unit, the Stack Firmware Synchronization featureautomatically synchronizes the firmware version with the version running onthe stack master. The synchronization operation may result in either anupgrade or a downgrade of firmware on the mismatched stack member. Inaddition, the running-config on the member is updated to match the masterswitch. The startup-config on the standby and member switches is notupdated to match the master switch due to configuration changes on themaster switch. Saving the startup config on the master switch also saves it tothe startup config on all the other stack members.The hardware configurationof every switch is updated to match the master switch (unit number, slotconfiguration, stack member number, etc.).Security FeaturesConfigurable Access and Authentication ProfilesYou can configure rules to limit access to the switch management interfacebased on criteria such as access type and source IP address of themanagement host. You can also require the user to be authenticated locally orby an external server, such as a RADIUS server.
