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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 5 Clustering Switches
Understanding Switch Clusters
Understanding Switch Clusters
A switch cluster is a group of connected Catalyst switches that are managed as a single entity. In a switch
cluster, 1 switch must be the command switch and up to 15 switches can be member switches. The total
number of switches in a cluster cannot exceed 16 switches. The command switch is the single point of
access used to configure, manage, and monitor the member switches. Cluster members can belong to
only one cluster at a time.
The benefits of clustering switches include:
•
Management of Catalyst switches regardless of their interconnection media and their physical
locations. The switches can be in the same location, or they can be distributed across a Layer 2 or
Layer 3 (if your cluster is using a Catalyst 3550 multilayer switch as a Layer 3 router between the
Layer 2 switches in the cluster) network. Cluster members are connected through at least one VLAN
in common with the command switch according to the connectivity guidelines described in the
“Automatic Discovery of Cluster Candidates and Members” section on page 5-4
. This section
includes some management VLAN considerations for the Catalyst 1900, Catalyst 2820,
Catalyst 2900 XL, Catalyst 2950, and Catalyst 3500 XL switches. For complete information about
these switches in a switch-cluster environment, refer to the software configuration guide for that
specific switch.
•
Command-switch redundancy if a command switch fails. One or more switches can be designated
as standby command switches to avoid loss of contact with cluster members. A cluster standby
group is a group of standby command switches.
•
Management of a variety of Catalyst switches through a single IP address. This conserves on IP
addresses, especially if you have a limited number of them. All communication with the switch
cluster is through the command switch IP address.
For other clustering benefits, see the
“Advantages of Using CMS and Clustering Switches” section on
page 1-6
.
Refer to the release notes for the list of Catalyst switches eligible for switch clustering, including which
ones can be command switches and which ones can only be member switches, and the required software
versions.
Command Switch Characteristics
A Catalyst 3550 command switch must meet these requirements:
•
It is running Cisco IOS Release 12.1(4)EA1 or later.
•
It has an IP address.
•
It has Cisco Discovery Protocol (CDP) version 2 enabled (the default).
•
It is not a command or member switch of another cluster.
Note
•
We strongly recommend that the highest-end, command-capable switch in the cluster be the
command switch:
•
If your switch cluster has a Catalyst 3550 switch, that switch should be the command switch.
•
If your switch cluster has Catalyst 2900 XL, Catalyst 2950, and Catalyst 3500 XL switches, the
Catalyst 2950 should be the command switch.
•
If your switch cluster has Catalyst 1900, Catalyst 2820, Catalyst 2900 XL, and Catalyst 3500 XL
switches, either the Catalyst 2900 XL or Catalyst 3500 XL should be the command switch.
