Stacking and VSS

StackWise/StackWise Plus enable separate physical switches to act as a single logical switch.

Cisco Catalyst 3750-E, 3750-X, and 3850 platforms.

Virtual Switching System (VSS)

Cisco Catalyst 4500R, 6500, and 8500.

VSS - configure two identical chassis to act as one logical switch.

One supervisor in one of the chassis controls the operation of the logical switch. If it fails, the supervisor in the other chassis takes over.

The chassis must be linked together by multiple interfaces that have been configured as a virtual switch link (VSL).

Route Processor Redundancy (RPR) - The redundant supervisor is only partially booted and initialized. To become ative, the Standby module must reload every module in the switch and initialize all supervisor functions.

Route Processor Redundancy Plus (RPR+) - The redundant supervisor is booted, allowing the supervisor and route engine to initialize. No L2/L3 functions are started. To become active, the Standby module finishes initializing without reloading other switch modules.

Stateful Switchover (SSO) - The redundant supervisor is fully booted and initialized. Startup and running configurations are are synchronized between the supervisor models. L2 information is maintained on both supervisors so that hardware switching can continue during a failover.

Single Server Mode (SRM) - Two route processors are being used, but one is active.
Dual Router Mode (DRM) - Two route processors are active at all times. HSRP is used to provide redundancy in DRM.

SRM is not compatible with RPR and RPR+, because the route processor portion is not initialized by the standby unit.

SRM is inherent with SSO, witch brings up the standby processor.