Sensor nodes can be compromised by attackers and inject large amounts of bogus data to exhaust network resources.A practical traceback mechanism is proposed
in which each forwarding node marks packets with a certain probability.By collecting enough packets
sink node will construct a path back to the source node.It is proved that the mechanism is secure against all forms of attacks and other two marking methods are proposed to improve the performance of the mechanism.Simulation results show that the mechanism is efficient and practical.