t trap indicates that the sending agent
has become the new root of the Spanning Tree; the
trap is sent by a bridge soon after its election
as the new root, e.g., upon expiration of the
Topology Change Timer immediately subsequent to
its election.  Implementation of this trap is
optional.

Change trap is sent by a bridge when
any of its configured ports transitions from the
Learning state to the Forwarding state, or from
the Forwarding state to the Blocking state.  The
trap is not sent if a newRoot trap is sent for the
same transition.  Implementation of this trap is
optional.

erTrap trap indicates that there was a Intruder
was detected on the port shown as ifIndex.