Denial of service attacks, viruses and worms are common tools for malicious adversarial behaviour in networks. In this paper we propose the use of our autonomic routing protocol, the Cognitive Packet Network (CPN), as a means to defend nodes from Distributed Denial of Service Attacks (DDoS), where one or more attackers generate flooding traffic from multiple sources towards selected nodes or IP addresses. We use both analytical and simulation modelling, and experiments on our CPN testbed, to evaluate the advantages and disadvantages of our approach in the presence of imperfect detection of DDoS attacks, and of false alarms.