Explanation/Reference:
Section: Considerations for Expanding an Existing Network Explanation
Explanation:
A maximum of two chassis may be connected to form a Virtual Switching System (VSS). VSS is a Cisco physical device virtualization feature that can enable a pair of chassis-based switches, such as the Cisco Catalyst 6500, to function as a single logical device. The switch pair is connected by an EtherChannel bundle known as a Virtual Switch Link (VSL). Using VSS enables an administrator to increase link utilization without adding physical connections or hardware. There are two identical supervisors in a VSS, one on each physical device, and one control plane. One of the supervisors is active, and the other is designated as hot-standby; the active supervisor manages the control plane. If the active supervisor in a VSS goes down, the hot-standby will automatically take over as the new active supervisor.
With VSS, access layer devices can connect to the switch pair by using several active, physical uplinks that are bundled together into a single logical link using Multi-chassis EtherChannel (MEC). Because all of the links in the bundle to the distribution switch pair are active, each access layer device is reduced to having a single logical link to the virtual distribution layer switch; therefore, Spanning Tree Protocol (STP) is no longer required to prevent loops. In addition, since there is only a single logical link to the virtual distribution layer switch, the access layer device can load balance traffic across all of its active links and the device does not need to rely on a First Hop Redundancy Protocol (FHRP) for convergence if a link in the MEC bundle fails.
You cannot connect nine physical chassis to form a VSS? however, you can use StackWise to link up to nine individual switches to function as a single switch. StackWise is a Cisco-proprietary technology that is used to provide Open Systems Interconnection (OSI) Layer 2 or Layer 3 connectivity between switches so that a stack of workgroup switches acts as a single device. StackWise switches are connected sequentially by stack cables: the first switch is connected to the second, the second switch is connected to the third, and so on until the last switch is connected to the first. If a stack cable is broken, the bandwidth of the stack will be reduced by 50 percent until the cable is fixed.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 4, Virtualization Technologies, pp. 153-157 Cisco: Campus 3.0 Virtual Switching System Design Guide: VSS Architecture and Operation