The Paper evaluates the performance of Bi-directional Shared Tree (BST) multicasting network with two sources and four receivers, attacked by five attackers. These attackers attack the source 1 in network by ICMP Ping Flood. Here we execute the simulation and draw network throughput between source 1 and source 2, queuing transmission delay and drop out data packets at source 1 for ping packet of size 16, 64 and 96 Bytes for 500, 1500 and 2500 ping packets per second. The simulation results indicate that throughput decreases with the increase in attack packet size and attack intensity, and remain constant for all values of intensity with larger packet size, delay increases with increase in attack packet size and decrease with increase in attacking intensity. Also, with the increase in attack packet size the number of dropped packets remain nearly same for different intensities.