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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 6 Clustering Switches
Planning a Switch Cluster
• Other Considerations for Cluster Standby Groups, page 6-10
• Automatic Recovery of Cluster Configuration, page 6-11
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 6-12.
Other Considerations for Cluster Standby Groups
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 2950 and 2955 switch, the standby
cluster command switches must also be Catalyst 2950 and 2955 switches. Refer to the switch
configuration guide of other cluster-capable switches for their requirements on standby cluster
command switches.
• Only one cluster standby group can be assigned to a cluster. You can have more than one
router-redundancy standby group.
• 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.
• Each standby-group member (Figure 6-6) must be connected to the cluster command switch through
the same VLAN. Each standby-group member must also be redundantly connected to each other
through at least one VLAN in common with the switch cluster.
Catalyst 1900, Catalyst 2820, Catalyst 2900 XL, Catalyst 2950, and Catalyst 3500 XL cluster
member switches must be connected to the cluster standby group through their management
VLANs. For more information about VLANs in switch clusters, see these sections:
–
“Discovery Through Different VLANs” section on page 6-7
–
“Discovery Through Different Management VLANs” section on page 6-7