26 Assembling a Switch StackUse only QSFP transceivers and QSFP cables (s eparately purchased) toconnect stacking ports as follows:1 Insert a QSFP cable in the bottom stacking port on the rightmost switch.2 Connect the upper stacking port on the next switch to the left.3 Continue connecting each switch to the next in this way until you reachthe leftmost switch in the stack.4 On the leftmost switch, connect the bottom stacking port to the upperstacking port on the rightmost switch to create a loop.NOTE: The resulting ring topology allows the entire stack to function as a singleswitch with resilient fail-over capabilities.If you do not connect the leftmost switch to the rightmost switch (Step 4), the stackoperates in a daisy-chain topology with less resiliency. Any failure in a non-edgestack unit causes a split stack.Configuring and Bringing Up a StackNOTE: Although stacking is supported on 40GbE ports on the base module or a2-Port 40GbE QSFP+ module, this section shows how to configure stacking only onthe base-module ports (Figure 1-9).To convert the 40GbE ports on the 2-Port QSFP+ module from their default 4x10GbEmode of operation to 40GbE mode to configure a stack, refer to "FlexIOTM Plug-inModules" on page 7. After the converting the ports to 40GbE, you do not have toreload the switch because a switch reload is required as part of the stackconfiguration procedure.After you attach the QSFP+ cables in a stack of MXL 10/40GbE Switches, toconfigure and bring up the stack, follow these steps:1 Connect the terminal to the console port on an MXL 10/40GbE Switch .Enter the following commands to access the CLI and configure the two40GbE ports on the base module for stacking mode:Login: usernamePassword: *****FTOS> enableFTOS# configureFTOS(conf)# stack-unit 0 stack-group 0FTOS(conf)# stack-unit 0 stack-group 1Where stack-unit 0 defines the default stack-unit number in the initialconfiguration of a switch; stack-group 0 defines the stack group for the