The invention discloses a 
software defined opportunity network 
DDoS defense method based on a block chain. Firstly, the characteristic that the SDN can perform logic 
centralized management and controlon a 
control layer is utilized; the network state is dynamically monitored in real time; then, the possibility of existence of a DDoS amplification 
attack is analyzed by analyzing the traffic characteristics obtained by monitoring, an attacker address is determined according to a 
traceability algorithm, and finally, a public accessible attacker 
blacklist is maintained by using a block chain architecture to assist an 
application layer in malicious traffic filtering so as to realize defense of the DDoS 
attack. According to the method, the 
attack source tracking accuracy is improved, the storage of the attack source 
blacklist address is realized in combination with the block chain architecture, and the attack source storage architecture based on the distributed account book technology can effectively prevent the data from being tampered or damaged while maintaining the 
data reliability. The whole network can perform filtering in a data packet receiving stage by inquiring a 
blacklist address, so that the DDoS attack is prevented from the source.