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GBIC Loop Configurations Not Supported Before
IOS Software Release 12.0(5)XU


GBIC Loop Configurations Not Supported Before
IOS Software Release 12.0(5)XU

GigaStack Gigabit Interface Converters (GBICs) installed in a stack support a loop configuration only if every device in the stack is running IOS software Release 12.0(5)XU (April 2000) or later or Release 12.1(4)EA1 or later for the Catalyst 3550 switches. For earlier software releases, these conditions create an illegal loop:

A GigaStack GBIC port within a cascaded-stack connection is connected to a GigaStack GBIC port of another stacked device that already has a GigaStack GBIC port connected to a device in that stack; both ports are in the same stack. See .

Figure 1 Incorrect Cabling of Switches in a Stack

A single GigaStack cable is inserted in port 1 and port 2 of the same GigaStack GBIC. See .

Figure 2 Incorrect Cabling in a Single Switch

In releases earlier than Release 12.0(5)XU, this loop causes excessive collision errors on the port and might cause the link to become unstable. This instability decreases performance on the links, and communication between the switches in the stack is adversely affected. For correct configuration scenarios, refer to the Catalyst GigaStack Gigabit Interface Converter Hardware Installation Guide.

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