# Multi-Constraint and Multi-Policy Path Hopping Active Defense Method Based on SDN
## 2 Related Works  
Path hopping is a method of dynamically adjusting network traffic paths and is one of the key technologies of MTD. It mainly resists eavesdropping by attackers and increases the difficulty and cost of attackers' detection by constantly changing the communication path between the two parties during communication, thereby improving the security of the network. In terms of resisting network attacks, to resist eavesdropping and DoS attacks, [PERSON] et al. [3] proposed a multi-path hopping scheme based on the \(n-k\) threshold to resist eavesdropping attacks. This scheme prevents attackers from obtaining a large amount of data in long-term monitoring by limiting the maximum data flow passing through the same path. [PERSON] et al. [4] proposed a random route mutation method (RRM) to resist DoS attacks and eavesdropping. This method transforms the problem of generating path hopping space into a constraint satisfaction problem; sets constraints in terms of capacity, overlap, and QoS; and generates paths using the SMT constraint solving method. The authors also proposed the implementation of this method in SDN network and traditional network architectures. However, this method uses pure random path selection, which may result in repeated use of paths. [PERSON] et al. [5] used game theory and SMT to select the hopping path according to the current state of the communication network and the attack methods used by the attacker, thereby improving the effectiveness of resisting attacks and effectively enhancing the security of static network communication. [PERSON] et al. [6] proposed a double hopping communication (DHC) scheme based on SDN to resist eavesdropping attacks by expanding the detection space. This scheme coordinates the hopping of multiple attributes such as IP address, communication path, and port number based on the SDN network architecture, providing diversity and uncertainty of network attributes and increasing the difficulty and cost to attackers. However, this method does not consider the situation of key nodes, leading to the repeated appearance of key nodes in multiple hopping cycles. [PERSON] et al. [7] proposed a path random hopping method that is automatically triggered by setting a traffic threshold to change the fixed hopping cycle defect in traditional hopping design. An improved ant colony algorithm was also designed to calculate the optimal hopping path. This method effectively resists the detection of attackers and enhances the unpredictability of system attributes while reducing consumption. [PERSON] et al. [8] proposed a technology of coordinated hopping of transmission paths and end addresses to resist global eavesdropping attacks. This technology constrains the overlap and capacity of paths. Through SMT constraint solving, it realizes multi-path and multi-attribute coordinated hopping according to a specific hopping cycle, increases the complexity of network attributes, and effectively improves its defense capability, but the complexity is high in the process of path solving. Based on this, [PERSON] et al. [9] designed a software-defined intranet dynamic defense system (SIDD) with the aim of increasing the difficulty of attacks by attackers. This scheme realizes the coordinated hopping of IP addresses and paths based on zero trust and isolates dynamic design ideas, achieving comprehensive protection of the network. [PERSON] et al. [10] designed a new architecture to resist eavesdropping attacks by assigning weights to each path and using this as the basis for transmission rate and selection probability. This method has, to some extent, increased the dispersion of data packets and effectively avoided the acquisition of effective key information by attackers during long-term monitoring. [PERSON] [11] proposed a new expanded route randomization (ERR) technology based on SDN. This technology uses an improved Floyd-Warshell algorithm to calculate all shortest paths between two points.