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Catalyst 2940 Switch Software Configuration Guide
78-15507-02
Chapter 5 Clustering Switches
Planning a Switch Cluster
Discovery Through Non-CDP-Capable and Noncluster-Capable Devices
If a command switch is connected to a non-CDP-capable third-party hub (such as a non-Cisco hub), it
can discover cluster-enabled devices connected to that third-party hub. However, if the command switch
is connected to a noncluster-capable Cisco device, it cannot discover a cluster-enabled device connected
beyond the noncluster-capable Cisco device.
Figure 5-2 shows that the command switch discovers the Catalyst 3500 XL switch, which is connected
to a third-party hub. However, the command switch does not discover the Catalyst 2940 switch that is
connected to a Catalyst 5000 switch.
Refer to the release notes for the Catalyst switches that can be part of a switch cluster.
Figure 5-2 Discovery Through Non-CDP-Capable and Noncluster-Capable Devices
Discovery Through the Same Management VLAN
A Catalyst 2900 XL command switch, a Catalyst 2950 command switch running a release earlier than
Cisco IOS Release 12.1(9)EA1, or a Catalyst 3500 XL command switch must connect to all cluster
members through its management VLAN. The default management VLAN is VLAN 1. For more
information about management VLANs, see the “Management VLAN” section on page 5-14.
Note You can avoid this limitation by using, whenever possible, a Catalyst 3550 command switch, a Catalyst
2950 command switch running Cisco IOS Release 12.1(9)EA1 or later, or a Catalyst 2940 command
switch. These command switches can manage cluster members even if they belong to different
management VLANs. See the “Discovery Through Different Management VLANs” section on page 5-6.
The command switch in Figure 5-3 has ports assigned to management VLAN 9. It discovers all but these
switches:
• Switches 7 and 10 because their management VLAN (VLAN 4) is different from the
command-switch management VLAN (VLAN 9)
• Switch 9 because automatic discovery does not extend beyond a noncandidate device, which is
switch 7
Command switch
Catalyst 5000 switch
(noncluster-capable)
Third-party hub
(non-CDP-capable)
Catalyst 3500 XL
candidate switch
Catalyst 2940
candidate switch
87798