Virtual Switching System (VSS)

Virtual Switching System (VSS) allows two Cisco Catalyst 6500 or 4500 switches to be connected together so that they appear to the network as a single switch. Other devices in the network will see the VSS configured switches as a single switch, which allows the engineer the ability to create multi chassis Ether-Channels between the VSS pair and other devices while appearing to other protocols like spanning-tree as a single switch.

 

What are the benefits of VSS?  

By far the best feature of VSS is NSF (Non Stop Forwarding) / SSO (Stateful Switchover) which allows the failure of a single device without any downtime. This is due to the routing table / CEF table etc. being stored in supervisor module of both chassis, allowing one device to take over when the other fails similar to the failover that occurs between supervisor modules in a switch equipped with dual supervisors.

Another great feature of VSS is the ability to have a single point of management  to make changes. Changes made to configuration or IOS on the supervisor of one device within the VSS pair are synchronized to the supervisor of the other device, similar to a 6500 or 4500 with dual supervisors or a 3750 stack.

VSS increases operational efficiency by simplifying the network, reducing switch management overhead by at least 50 percent.

– Single configuration file and node to manage. Removes the need to configure redundant switches twice with identical policies.

– Only one gateway IP address is required per VLAN, instead of the three IP addresses per VLAN used today.

– Removes the need for Hot Standby Router Protocol (HSRP), Virtual Router Redundancy Protocol (VRRP), and Gateway Load Balancing Protocol (GLBP) 

– CiscoWorks LAN Management System (LMS) 3.0 can be used to centrally manage a Cisco Catalyst 6500 virtual switch as a single entity. 

- VSS boosts nonstop communications

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If for some rare reason all Virtual Switching Link (VSL) connections are lost between the virtual switch members leaving both the virtual switch members up, the VSS will transition to the dual active recovery mode.
In the dual active recovery mode, all interfaces except the VSL interfaces are in an operationally shut down state in the formerly active virtual switch member. The new active virtual switch continues to forward traffic on all links.