The stack IPv6 address of a stackable system. A non-stackable system should never return an instance of this object, nor allow writes to this object. Note that in standalone mode, this will still be the stack IPv6 address, even though it is not in use. When in stack mode, the IPv6 address of individual units can be found in the s5ChasComTable in the s5Chassis MIB (and note that these addresses will not be in use when in stack mode).