Specifications

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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 7 Clustering Switches
Planning a Switch Cluster
Automatic Discovery of Cluster Candidates and Members
The command switch uses Cisco Discovery Protocol (CDP) to discover member switches, candidate
switches, neighboring switch clusters, and edge devices in star or cascaded topologies.
Note Do not disable CDP on the command switch, on cluster members, or on any cluster-capable switches that
you might want a command switch to discover. For more information about CDP, see Chapter 21,
“Configuring CDP.”
Following these connectivity guidelines ensures automatic discovery of the switch cluster, cluster
candidates, connected switch clusters, and neighboring edge devices:
• Discovery through CDP Hops, page 7-6
• Discovery through Non-CDP-Capable and Noncluster-Capable Devices, page 7-8
• Discovery through the Same Management VLAN, page 7-9
• Discovery through Different Management VLANs, page 7-10
• Discovery of Newly Installed Switches, page 7-11
Discovery through CDP Hops
By using CDP, a command switch can discover switches up to seven CDP hops away (the default is
three hops) from the edge of the cluster. The edge of the cluster is where the last member switches are
connected to the cluster and to candidate switches. For example, member switches 9 and 10 in Figure 7-1
are at the edge of the cluster.
You can set the number of hops the command switch searches for candidate and member switches by
selecting Cluster > Hop Count. When new candidate switches are added to the network, the command
switch discovers them and adds them to the list of candidate switches.
In Figure 7-1, the command switch is running a release earlier than Release 12.1(9)EA1 and has ports
assigned to management VLAN 16. In Figure 7-2, the command switch is running Release 12.1(9)EA1
or later and has ports assigned to VLANs 16 and 62. The CDP hop count is three. Each command switch
discovers switches 11, 12, 13, and 14 because they are within three hops from the edge of the cluster. It
does not discover switch 15 because it is four hops from the edge of the cluster.