Cisco 6500 - Manual (Page 13)

4-13
Cisco IOS Software Configuration Guide, Release 12.2SX
OL-13013-06
Chapter 4 Configuring Virtual Switching Systems
Understanding Virtual Switching Systems
Failed Chassis Recovery
If the VSS active chassis or supervisor engine fails, the VSS initiates a stateful switchover (SSO) and
the former VSS standby supervisor engine assumes the VSS active role. The failed chassis performs
recovery action by reloading the supervisor engine.
If the VSS standby chassis or supervisor engine fails, no switchover is required. The failed chassis
performs recovery action by reloading the supervisor engine.
The VSL links are unavailable while the failed chassis recovers. After the chassis reloads, it becomes
the new VSS standby chassis and the VSS reinitializes the VSL links between the two chassis.
The switching modules on the failed chassis are unavailable during recovery, so the VSS operates only
with the MEC links that terminate on the VSS active chassis. The bandwidth of the VSS is reduced until
the failed chassis has completed its recovery and become operational again. Any devices that are
connected only to the failed chassis experience an outage.
Note The VSS may experience a brief data path disruption when the switching modules in the VSS standby
chassis become operational after the SSO.
After the SSO, much of the processing power of the VSS active supervisor engine is consumed in
bringing up a large number of ports simultaneously in the VSS standby chassis. As a result, some links
might be brought up before the supervisor engine has configured forwarding for the links, causing traffic
to those links to be lost until the configuration is complete. This condition is especially disruptive if the
link is an MEC link. Two methods are available to reduce data disruption following an SSO:
• Beginning in Cisco IOS Release 12.2(33)SXH2, you can configure the VSS to activate non-VSL
ports in smaller groups over a period of time rather than all ports simultaneously. For information
about deferring activation of the ports, see the
“Configuring Deferred Port Activation During VSS
Standby Recovery” section on page 4-44 .
• You can defer the load sharing of the peer switch’s MEC member ports during reestablishment of
the port connections. See the
“Failed Chassis MEC Recovery” section on page 4-16 for details about
load share deferral.
VSL Failure
To ensure fast recovery from VSL failures, fast link notification is enabled in virtual switch mode on all
port channel members (including VSL ports) whose hardware supports fast link notification.
Note Fast link notification is not compatible with link debounce mechanisms. In virtual switch mode, link
debounce is disabled on all port channel members.
If a single VSL physical link goes down, the VSS adjusts the port group so that the failed link is not
selected.
If the VSS standby chassis detects complete VSL link failure, it initiates a stateful switchover (SSO). If
the VSS active chassis has failed (causing the VSL links to go down), the scenario is chassis failure, as
described in the previous section.
If only the VSL has failed and the VSS active chassis is still operational, this is a dual-active scenario.
The VSS detects that both chassis are operating in VSS active mode and performs recovery action. See
the
“Dual-Active Detection” section on page 4-22 for additional details about the dual-active scenario.