Dell POWEREDGE M1000E - Manual (Page 60)

60 Switch Features
Master Failover with Transparent Transition
The stacking feature supports a Standby or backup unit that assumes the
Master unit role if the Master unit in the stack fails. As soon as a Master
failure is detected in the stack, the Standby unit initializes the control plane
and enables all other stack units with the current configuration. The Standby
unit maintains a synchronized copy of the running configuration for the
stack.
Nonstop Forwarding on the Stack
The Nonstop Forwarding (NSF) feature allows the forwarding plane of stack
units to continue to forward packets while the control and management
planes restart as a result of a power failure, hardware failure, or software fault
on the stack management unit. This type of operation is called nonstop
forwarding. When the management unit fails, only the switch ASICs on the
management unit need to be restarted.
Hot Add/Delete and Firmware Synchronization
You can add and remove units to and from the stack without cycling the
power. When you add a unit, the Stack Firmware Synchronization feature
automatically synchronizes the firmware version with the version running on
the stack master. The synchronization operation may result in either upgrade
or downgrade of firmware on the mismatched stack member.
Security Features
Configurable Access and Authentication Profiles
You can configure rules to limit access to the switch management interface
based on criteria such as access type and source IP address of the
management host. You can also require the user to be authenticated locally or
by an external server, such as a RADIUS server.
For information about configuring access and authentication profiles, see
"Controlling Management Access" on page 171.