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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
78-6511-05
Chapter 5 Clustering Switches
Planning a Switch Cluster
Standby Command Switches
Because a command switch manages the forwarding of all communication and
configuration information to all the cluster members, we strongly recommend that
you configure a standby command switch to take over if the command switch
fails. We also recommend redundant cabling from the standby command switch
to the switch cluster.
IOS Release 12.0(5)XU and higher supports a version of the Hot Standby Router
Protocol (HSRP) so that you can configure a standby group of command switches.
A standby group is a group of switches that meet the requirements described in
the “Standby Command Switch Characteristics” section on page 5-3.
Note Catalyst 2900 XL and Catalyst 3500 XL switches running releases earlier
than IOS Release 12.0(5)XU can belong to clusters supported by standby
command switches, but they cannot belong to a standby group.
The standby group of command switches are ranked according to a set of
user-defined priorities. Switches are ranked first by the number of links they have
and second by the switch speed. If switches have the same number of links and
speed, they are listed alphabetically. The member switch with the highest priority
in the group is the standby command switch. The standby group is bound to the
switch cluster so that the standby command switch becomes active if the primary
command switch fails.
You assign a unique virtual IP address to the standby group. The primary
command switch receives member traffic destined for the virtual IP address. To
manage the standby group, you must access the primary command switch through
the virtual IP address, not through the command-switch IP address. If HSRP is
enabled and you use the command-switch IP address, you will be prompted a
second time for a password when you move between Cluster Builder and VSM.
Figure 5-1 shows a group of switches with a standby command switch.
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