Stack configuration 491. Base Unit2. Cascade Cable3. Cascade Cable (used for return)Initial stack installationDuring the initial installation of the stack, the software automaticallydetermines the physical order of all units in the stack according to theposition of the base unit within the stack. Thereafter, the individual unitsmaintain their original unit numbering, even if the position of one or moreunits in the stack is changed.For example, when the stack is initially powered, the base unit becomes unit1 and the unit that the base unit connects to (via the Cascade Down cable)becomes unit 2 (and the next unit is unit 3 and so on), until the maximumstack configuration (up to 8 units) is reached. If the base unit is changed toanother unit in the stack, the new base unit keeps its original unit numberin the stack.Stack MAC addressWhen a switch participates in a stack configuration, a stack MAC address isautomatically assigned during stack initialization. The stack MAC address isthe base unit MAC address plus 1. If another unit in the stack is assignedas the base unit, the new stack MAC address is the MAC address of thenew base unit plus 1. The original stack IP address still applies to the newbase unit.Stack configurationsDue to stack parameters being associated with the base unit, the physicalstack order depends on the base unit position and whether the stack isconfigured cascade up (stack up) or cascade down (stack down). Thisdesignation depends on the stack cabling arrangement.The system automatically numbers the physical units based on thedesignated base unit (Unit 1). In a cascade down configuration, the baseunit is physically located as the top unit in the stack. The cable connected tothe Cascade Down connector of the base unit terminates in the Cascade Upconnector on the next unit in the stack which is physically located below thebase unit. This next unit is designated Unit 2. The stack is wired downwardthrough the units and the system continues to number in this mannerthroughout the stack. In this configuration, the base unit discovers thestack in a cascade down (stack down) direction. The following illustrationdemonstrates a cascade down (stack down) configuration.Nortel Ethernet Routing Switch 2500 SeriesOverview — System ConfigurationNN47215-500 (323162-B) 02.02 Standard4.1 19 November 2007Copyright © 2007, Nortel Networks.
