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Catalyst 2940 Switch Software Configuration Guide
78-15507-02
Chapter 5 Clustering Switches
Planning a Switch Cluster
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 5-4
• Discovery Through Non-CDP-Capable and Noncluster-Capable Devices, page 5-5
• Discovery Through the Same Management VLAN, page 5-5
• Discovery Through Different Management VLANs, page 5-6
• Discovery of Newly Installed Switches, page 5-7
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 5-1
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 5-1, the command switch 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.
Figure 5-1 Discovery Through CDP Hops
Command switch
Member
switch 10
Member
switch 8
Member
switch 9
VLAN 62
Edge of
cluster
VLAN 16
Switch 11
candidate
switch
Candidate
switches
Switch 12
Switch 13
Switch 14
Switch 15
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