Software defined networking (SDN) improves the flexibility and programmability of the network by separating the control plane and the data plane and effectively realizes the global control of the network infrastructure. However, the centralized structure design of SDN exposes the controller to potential threats. Attackers have used the active flow table delivery mode to launch distributed denial of service (DDoS) attacks on the SDN controller, resulting in the controller failure and seriously affecting the network performance. To overcome this problem, this paper proposes a defense framework called CC-Guard. The framework consists of four modules: attack detection triggering, switch migration, anomaly detection, and mitigation. Among them, the attack detection trigger module improves the system’s timely response to DDoS attacks. The switch migration module effectively unclogs the controller congestion problem and provides convenience for network flow transmission. The anomaly detection module uses a coarse-grained method for two-stage detection, which improves the detection accuracy. The mitigation module uses the idea of cross-domain cooperation of the controller to clear the abnormal flow in the blacklist. Experimental results show that our proposed CC-Guard has real-time DDoS attack defense capability and high detection accuracy, as well as efficient network resource utilization.

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Recently Fiori obtained the local density formulas of unimodular lattices over dyadic local fields, but his results have contradictions with Pfeuffer's and Körner's results for rank 3 case, and in some cases his formulas of rank 4 have fractions in the exponent part which is not compatible with the definition of local density. In this paper, using Siegel's mass formula and neighbor lattice methods we obtain a relation between local density and the number of neighbor lattices of dyadic unimodular lattices. Using the relation we get the local densities of unimodular lattices of ranks 3 and 4 over dyadic local fields. Combining these with the results of Pfeuffer, we can obtain the local density formulas of general unimodular lattices over dyadic local fields. Keywords dyadic unimodular lattice, local density, Siegel's mass formula, neighbor lattice MSC(2010)11E08, 11E12

In this paper, we prove that there exist indecomposable lattices of ranks 5 and 6 over a Hasse domain of any global function field in which [Formula: see text] is not a square, which solves a problem proposed by Gerstein.