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Cisco EtherSwitch Service Modules Feature Guide
Information About the Cisco EtherSwitch Service Modules
29
Cisco IOS Release 12.2(25)SEC
• Each standby-group member (Figure 7) must be connected to the cluster command switch through
the same VLAN. In this example, the cluster command switch and standby cluster command
switches are Cisco EtherSwitch service module cluster command switches. Each standby-group
member must also be redundantly connected to each other through at least one VLAN in common
with the switch cluster.
For more information about VLANs in switch clusters, see these sections:
–
“Discovery of Candidates and Members Through Different VLANs” section on page 24
–
“Discovery of Candidates and Members Through Different Management VLANs” section on
page 24
Figure 7 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 Cisco EtherSwitch service module 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
again add these cluster member switches to the cluster.
101326
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