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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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Chapter 6      Configuring the System
Configuring STP
Limitations
The following limitations apply to CSUF:
• CSUF uses the Gigastack GBIC and runs on all Catalyst 3500 XL switches 
but only on modular Catalyst 2900 XL switches.
• Up to nine stack switches can be connected through their stack ports to the 
multidrop backbone. Only one stack port per switch is supported.
• Each stack switch can be connected to the STP backbone through one uplink.
• Up to 64 VLANs are supported.
Connecting the Stack Ports
A fast transition occurs across the stack of switches if the multidrop backbone 
connections are a continuous link from one GigaStack GBIC to another as shown 
in Figure 6-8. In addition, follow these guidelines:
• Do not connect alternate stack root ports to stack ports. 
• Only one stack port is supported per switch.
• All stack ports on the stack of switches must be connected to the multidrop 
backbone.
• You can connect the open ports on the top and bottom GigaStack GBICs 
within the same stack to form a redundant link.