The index of the eventEntry in the RMON MIB that
will be triggered whenever the value of
hpicfBackupLinkState changes from 'usingPrimary' to
'usingBackup'. The eventEntry identified by a
particular value of this index is the same as
identified by the same value of the eventIndex
object. If there is no corresponding entry in the
eventTable, then no association exists. In
particular, if this value is zero, no associated
event will be generated, as zero is not a valid
event index.