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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter 6 Clustering Switches
Planning a Switch Cluster
Automatic discovery has these limitations:
• This limitation applies only to clusters that have Catalyst 2950, Catalyst 2960, Catalyst 2970,
Catalyst 3550, Catalyst 3560, Catalyst 3560-E, Catalyst 3750, and Catalyst 3750-E 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.
IP Addresses
You must assign IP information to a cluster command switch. You can assign more than one IP address
to the cluster command switch, and you can access the cluster through any of the command-switch IP
addresses. If you configure a cluster standby group, you must use the standby-group virtual IP address
to manage the cluster from the active cluster command switch. Using the virtual IP address ensures that
you retain connectivity to the cluster if the active cluster command switch fails and that a standby cluster
command switch becomes the active cluster command switch.
If the active cluster command switch fails and the standby cluster command switch takes over, you must
either use the standby-group virtual IP address or any of the IP addresses available on the new active
cluster command switch to access the cluster.
You can assign an IP address to a cluster-capable switch, but it is not necessary. A cluster member switch
is managed and communicates with other cluster member switches through the command-switch IP
address. If the cluster member switch leaves the cluster and it does not have its own IP address, you must
assign an IP address to manage it as a standalone switch.
For more information about IP addresses, see Chapter 3, “Assigning the Switch IP Address and Default
Gateway.”
Hostnames
You do not need to assign a host name to either a cluster command switch or an eligible cluster member.
However, a hostname assigned to the cluster command switch can help to identify the switch cluster.
The default hostname for the switch is Switch.