Cisco is leaving VSS technology and moving towards StackWise. StackWise Virtual (SV) combines two switches into a single logical network entity from the network control plane and management perspectives. It uses Cisco IOS ® Stateful Switchover (SSO) technology, as well as Non-Stop Forwarding (NSF) extensions to routing protocols, to provide seamless traffic failover when one of the devices fails over. To neighboring devices, a StackWise Virtual domain appears as a single logical switch or router.