Vss functionality – Cisco 6500 User Manual
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Cisco IOS Software Configuration Guide, Release 12.2SX
OL-13013-06
Chapter 4 Configuring Virtual Switching Systems
Understanding Virtual Switching Systems
VSS Functionality
The following sections describe the main functionality of a VSS:
•
Redundancy and High Availability, page 4-6
•
•
•
VSS Quad-Sup Uplink Forwarding, page 4-7
•
Interface Naming Convention, page 4-8
•
Redundancy and High Availability
In a VSS, supervisor engine redundancy operates between the VSS active and VSS standby chassis,
using stateful switchover (SSO) and nonstop forwarding (NSF). The peer chassis exchange configuration
and state information across the VSL and the VSS standby supervisor engine runs in hot VSS standby
mode.
The VSS standby chassis monitors the VSS active chassis using the VSL. If it detects failure, the VSS
standby chassis initiates a switchover and takes on the VSS active role. When the failed chassis recovers,
it takes on the VSS standby role.
If the VSL fails completely, the VSS standby chassis assumes that the VSS active chassis has failed, and
initiates a switchover. After the switchover, if both chassis are VSS active, the dual-active detection
feature detects this condition and initiates recovery action. For additional information about dual-active
detection, see the
“Dual-Active Detection” section on page 4-22
Packet Handling
The VSS active supervisor engine runs the Layer 2 and Layer 3 protocols and features for the VSS and
manages the DFC modules for both chassis.
The VSS uses VSL to communicate protocol and system information between the peer chassis and to
carry data traffic between the chassis when required.
Both chassis perform packet forwarding for ingress traffic on their interfaces. If possible, ingress traffic
is forwarded to an outgoing interface on the same chassis to minimize data traffic that must traverse the
VSL.
Because the VSS standby chassis is actively forwarding traffic, the VSS active supervisor engine
distributes updates to the VSS standby supervisor engine PFC and all VSS standby chassis DFCs.
System Management
The VSS active supervisor engine acts as a single point of control for the VSS. For example, the VSS
active supervisor engine handles OIR of switching modules on both chassis. The VSS active supervisor
engine uses VSL to send messages to and from local ports on the VSS standby chassis.
The command console on the VSS active supervisor engine is used to control both chassis. In virtual
switch mode, the command console on the VSS standby supervisor engine blocks attempts to enter
configuration mode.
The VSS standby chassis runs a subset of system management tasks. For example, the VSS standby
chassis handles its own power management.