Cisco 6500 - Manual (Page 4)

4-4
Cisco IOS Software Configuration Guide, Release 12.2SX
OL-13013-06
Chapter 4 Configuring Virtual Switching Systems
Understanding Virtual Switching Systems
Virtual Switch Link
For the two chassis of the VSS to act as one network element, they need to share control information and
data traffic.
The virtual switch link (VSL) is a special link that carries control and data traffic between the two
chassis of a VSS, as shown in
Figure 4-3 . The VSL is implemented as an EtherChannel with up to eight
links. The VSL gives control traffic higher priority than data traffic so that control messages are never
discarded. Data traffic is load balanced among the VSL links by the EtherChannel load-balancing
algorithm.
Figure 4-3 Virtual Switch Link
When you configure VSL all existing configurations are removed from the interface except for specific
allowed commands. When you configure VSL, the system puts the interface into a restricted mode.
When an interface is in restricted mode, only specific configuration commands can be configured on the
interface.
The following VSL configuration commands are not removed from the interface when it becomes
restricted:
• mls qos trust cos
• mls qos channel-consistency
• description
• logging event
• load-interval
• vslp
• port-channel port
When in VSL restricted mode, only these configuration commands are available:
• channel-group
• default
• description
• exit
• load-interval
• logging
• mls
• mls ip
181322
Virtual switch link
(VSL)
Virtual switch
Chassis 1 Chassis 2