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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 6 Clustering Switches Planning a Switch Cluster
Virtual IP Addresses
You need to assign a unique virtual IP address and group number and name to the cluster standby group.
This information must be configured on a specific VLAN or routed port on the active cluster command
switch. The active cluster command switch receives traffic destined for the virtual IP address. To manage
the cluster, you must access the active cluster command switch through the virtual IP address, not
through the command-switch IP address. This is in case the IP address of the active cluster command
switch is different from the virtual IP address of the cluster standby group.
If the active cluster command switch fails, the standby cluster command switch assumes ownership of
the virtual IP address and becomes the active cluster command switch. The passive switches in the
cluster standby group compare their assigned priorities to decide the new standby cluster command
switch. The passive standby switch with the highest priority then becomes the standby cluster command
switch. When the previously active cluster command switch becomes active again, it resumes its role as
the active cluster command switch, and the current active cluster command switch becomes the standby
cluster command switch again. For more information about IP address in switch clusters, see the “IP
Addresses” section on page 6-13.
Other Considerations for Cluster Standby Groups
Note For additional considerations about cluster standby groups in switch stacks, see the “Switch Clusters and
Switch Stacks” section on page 6-14.
These requirements also apply:
• Standby cluster command switches must be the same type of switches as the cluster command
switch. For example, if the cluster command switch is a Catalyst 3750-E or Catalyst 3750-X switch,
the standby cluster command switches must also be Catalyst 3750-E or Catalyst 3750-X switches.
See the switch configuration guide of other cluster-capable switches for their requirements on
standby cluster command switches.
If your switch cluster has a Catalyst 3750-X switch or a switch stack, it should be the cluster
command switch. If not, when the cluster has a Catalyst 3750-E switch or switch stack, that switch
should be the cluster command switch.
• Only one cluster standby group can be assigned to a cluster. You can have more than one
router-redundancy standby group.
An HSRP group can be both a cluster standby group and a router-redundancy group. However, if a
router-redundancy group becomes a cluster standby group, router redundancy becomes disabled on
that group. You can re-enable it by using the CLI. For more information about HSRP and router
redundancy, see Chapter 44, “Configuring HSRP.”
• All standby-group members must be members of the cluster.
Note There is no limit to the number of switches that you can assign as standby cluster command
switches. However, the total number of switches in the cluster—which would include the
active cluster command switch, standby-group members, and cluster member
switches—cannot be more than 16.