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Virtual Switching System
Q. What is a virtual switching system (VSS)? A. A VSS is network system virtualization technology that pools multiple Cisco® Catalyst® 6500 Series Switches
into one virtual switch, increasing operational efficiency, boosting nonstop communications, and scaling system bandwidth capacity to 1.4 Tbps. At the initial phase, a VSS will allow two physical CiscoCatalyst 6500 Series Switches to operate as a single logical virtual switch called a virtual switching system 1440 (VSS1440). (See Figure 1.)
Figure 1. Virtual Switching System 1440 Compared to Traditional Network Design

Q. What is a VSS1440? A. VSS1440 refers to the VSS formed by two Cisco Catalyst 6500 Series Switches with the Virtual Switching
Supervisor 720-10GE. In a VSS, the data plane andswitch fabric with capacity of 720 Gbps of supervisor engine in each chassis are active at the same time on both chassis, combining for an active 1400-Gbps switching capacity per VSS. Only one of the virtual switch members has the active control plane. Both chassis are kept in sync with the interchassis Stateful Switchover (SSO) mechanism along with Nonstop Forwarding (NSF) to provide nonstopcommunication even in the event of failure of one of the member supervisor engines or chassis.

Q. What are the benefits of VSS? A. VSS offers superior benefits compared to traditional Layer 2/Layer 3 network design. Benefits can be grouped
into four main categories: 1. VSS increases operational efficiency by simplifying the network, reducing switch management overhead by at least 50 percent.
●Single point of management, IP address, and routing instance for the Cisco Catalyst 6500 virtual switch 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.
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© 2009 Cisco Systems, Inc. All rights reserved. Thisdocument is Cisco Public Information.

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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.

Multichassis EtherChannel (MEC) is a Layer 2multipathing technology that creates simplified loop-free topologies, eliminating the dependency on Spanning Tree Protocol, which can still be activated to protect strictly against any user misconfiguration.

Flexible deployment options. The underlying physical switches do not have to be colocated. The two physical switches are connected with standard 10 Gigabit Ethernet interfaces and as such can belocated any distance based on the distance limitation of the chosen 10 Gigabit Ethernet optics. For example, with X210GB-ER 10 Gigabit Ethernet optics, the switches can be located up to 40 km apart.


VSS boosts nonstop communications.

Interchassis stateful failover results in no disruption to applications that rely on network state information (for example, forwarding table info,NetFlow, Network Address Translation [NAT], authentication, and authorization). VSS eliminates L2/L3 protocol reconvergence if a virtual switch member fails, resulting in deterministic subsecond virtual switch recovery.

Utilizes EtherChannel (802.3ad or Port Aggregation Protocol (PAgP) for deterministic subsecond Layer 2 link recovery, removing the dependency on Spanning Tree Protocol forlink recovery.


VSS scales system bandwidth capacity to 1.4 Tbps.

Activates all available Layer 2 bandwidth across redundant Cisco Catalyst 6500 Series Switches with automatic, even load sharing. Link load sharing is optimized because it is based on more granular information, such as L2/L3/L4 parameters, unlike virtual LAN (VLAN)-based load balancing in Spanning Tree Protocol...
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