Specifications

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Catalyst 2970 Switch Software Configuration Guide
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Chapter 5 Clustering Switches
Planning a Switch Cluster
• Each standby-group member (Figure 5-6) 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 5-7
– “Discovery Through Different Management VLANs” section on page 5-8
Figure 5-6 VLAN Connectivity between Standby-Group Members and Cluster Members
Automatic Recovery of Cluster Configuration
The active cluster command switch continually forwards cluster-configuration information (but not
device-configuration information) to the standby cluster command switch. This ensures that the standby
cluster command switch can take over the cluster immediately after the active cluster command switch
fails.
Automatic discovery has these limitations:
• This limitation applies only to clusters that have Catalyst 2950, Catalyst 3550, and Catalyst 3750
command and standby cluster command switches: If the active cluster command switch and standby
cluster command switch become disabled at the same time, the passive cluster command switch with
the highest priority becomes the active cluster command switch. However, because it was a passive
standby cluster command switch, the previous cluster command switch did not forward
cluster-configuration information to it. The active cluster command switch only forwards
cluster-configuration information to the standby cluster command switch. You must therefore
rebuild the cluster.
• This limitation applies to all clusters: If the active cluster command switch fails and there are more
than two switches in the cluster standby group, the new cluster command switch does not discover
any Catalyst 1900, Catalyst 2820, and Catalyst 2916M XL cluster member switches. You must
re-add these cluster member switches to the cluster.
• This limitation applies to all clusters: If the active cluster command switch fails and becomes active
again, it does not discover any Catalyst 1900, Catalyst 2820, and Catalyst 2916M XL cluster
member switches. You must again add these cluster member switches to the cluster.
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Management
VLAN 16
Standby
command switch
VLAN 16
VLAN 9
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VLAN 9
Command
switch
Passive
command switch
Member switches
Management
VLAN 9
VLANs 9,16 VLANs 9,16
Management
VLAN 16
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