Alcatel OS6855-24 User Guide - Page 165

Managing OmniSwitch 6855 Series Stacks Stack Cabling Stack Cabling Switches in a stack are connected to each other with either copper or fiber stacking cables that are available in various lengths. Fiber can be used with an SFP+ transceiver. Stacking cables for OmniSwitches can be connected in any pattern. In other words, the cable connected to stacking port A of one switch can be connected to either stacking port A or stacking port B of the adjacent switch. However, it is strongly recommended that the cabling pattern remains consistent across the stack. In addition, for a stack to have effective redundancy, a redundant stacking cable must be installed between the upper-most and bottom-most switch at all times. This provides effective failover in the event of a sta cking link or module failure within the stack. The diagram below shows two recommended stacking cable patterns. Refer to "Stacking Cables" on page 2-42 for cable specifications. Note. When planning the stack cabling configuration, keep in mind that the switch connected to stacking port A of the primary switch will be assigned the secondary management role by default. The diagram below is for example purposes only, currently only four OS6855-U24X switches can be stacked at a time. A B A stack of switches in a crossed (stacking port A to stacking port B) configuration. Note that a redundant stacking cable connection exists between the top and bottom switches. This connection is required for effective redundancy across the stack. A B A stack of switches in a straight (stacking port A to stacking port A; stacking port B to stacking port B) configuration. Note that a redundant stacking cable connection exists between the top and bottom switches. Again, this connection is required for effective redundancy across the stack. Examples of Stacking Cable Patterns (Chassis Rear Panels Shown) OmniSwitch 6855 Series Hardware Users Guide September 2011 page 7-17