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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 6 Clustering Switches
Planning a Switch Cluster
Figure 6-6 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, Catalyst 3560, 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.
When the previously active cluster command switch resumes its active role, it receives a copy of the
latest cluster configuration from the active cluster command switch, including members that were added
while it was down. The active cluster command switch sends a copy of the cluster configuration to the
cluster standby group.
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Management
VLAN 16
Standby
command device
VLAN 16
VLAN 9
VLAN 9
Command
device
Passive
command device
Member devices
Management
VLAN 9
VLANs 9,16 VLANs 9,16
Management
VLAN 16