5-3
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)SG
OL-30933-01
Chapter 5 Configuring Virtual Switching Systems
Understanding Virtual Switching Systems
• Hardware Requirements, page 5-9
• Understanding VSL Topology, page 5-11
Key Concepts
The VSS incorporates the following key concepts:
• Virtual Switching System, page 5-3
• VSS Active and VSS Standby Switch, page 5-3
• Virtual Switch Link, page 5-4
• Multichassis EtherChannel, page 5-5
Virtual Switching System
A VSS combines a pair of switches into a single network element. For example, a VSS in the distribution
layer of the network interacts with the access and core networks as if it were a single switch. See
Figure 5-2.
An access switch connects to both switches of the VSS using one logical port channel. The VSS manages
redundancy and load balancing on the port channel. This capability enables a loop-free Layer 2 network
topology. The VSS also simplifies the Layer 3 network topology by reducing the number of routing peers
in the network.
Figure 5-2 VSS in the Distribution Network
VSS Active and VSS Standby Switch
When you create or restart a VSS, the peer switches negotiate their roles. One switch becomes the VSS
Active switch, and the other switch becomes the VSS Standby switch.
The VSS Active controls the VSS, running the Layer 2 and Layer 3 control protocols for the switching
modules on both switches. The VSS Active switch also provides management functions for the VSS,
such as module online insertion and removal (OIR) and the console interface.
The VSS Active and VSS Standby switches perform packet forwarding for ingress data traffic on their
locally hosted interfaces. However, the VSS Standby switch sends all control traffic to the VSS Active
switch for processing.
181321
Virtual Distribution Switch Virtual Distribution Switch
Access
Access
Physical view Logical view
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