Vss Configuration Guidelines And Restrictions - Cisco Catalyst 4500 Series Software Configuration Manual

VSS Configuration Guidelines and Restrictions

System Initialization
If you boot both switches simultaneously, the switch configured as Switch 1 boots as VSS Active and
the one with Switch 2 boots as VSS Standby. If priority is configured, the higher priority switch becomes
active.
If you boot only one switch, the VSL ports remain inactive, and the switch boots as VSS Active. When
you subsequently boot the other switch, the VSL links become active, and the new switch boots as VSS
Standby. Because preemption is not supported, if a VSS Active is already running, the peer switch would
always receive the VSS Standby role, even if its priority is higher than that of the Active's.
VSL Down
If the VSL is down when both switches try to boot up, the situation is similar to a dual-active scenario.
One of the switch becomes VSS Active and the other switch initiates recovery from the dual-active
scenario. For further information, see the
VSS Configuration Guidelines and Restrictions
The following sections describe restrictions and guidelines for VSS configuration:
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General VSS Restrictions and Guidelines
When configuring the VSS, note the following guidelines and restrictions:
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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
5-28
startup-config. This means that if the Active switch was running prior to the Standby switch and
unsaved configurations existed, they would be written to the startup-config if the Standby switch
sends mismatched VSL information.
General VSS Restrictions and Guidelines, page 5-28
Multichassis EtherChannel Restrictions and Guidelines, page 5-29
Dual-Active Detection Restrictions and Guidelines, page 5-30
Beginning in Cisco IOS XE 3.8.0E, Quad-Supervisor VSS mode is supported on the Catalyst 4500
series switches.
In Cisco IOS XE 3.4.0E (15.1(2)SG, E, VSS did not support SMI (both Director and Client).
Beginning with Cisco IOS XE 3.5.0E (15.2(1)E, VSS supports SmartInstall Director but not SMI
Client.
Beginning with Cisco IOS XE 3.6.0E (15.2(2)E), VSS supports SmartInstall Director and SMI
Client.
VSS [mode] is transparent to SMI except for the changes in interface names.
The SMI Director has only one instance on VSS and runs on the VSS active switch. The standby
Catalyst 4500 switch in a VSS is not listed as a director in the output of the sh vstack status
command.
The VSS configurations in the startup-config file must match on both switches; that is, the domain
must match, the switch ID must be unique, and the VSL ports' information must match the physical
connection.
Chapter 5
"Configuring Dual-Active Detection" section on page
Configuring Virtual Switching Systems
5-52.