## 3 Security in SDNFV
### SDN Security Issues  
As discussed in the previous section, the primary objective of SDN architecture is the separation of data and control planes. Consequently, the SDN architecture (refer to Figure 1) comprises three layers: the application layer, the control layer, and the infrastructure layer, each containing specific subcomponents:  
* Network elements (NE) situated in the infrastructure layer.
* SDN controllers located in the control layer.
* SDN-enabled applications situated in the application layer.  
While legacy networks possess a single type of component (network devices), the SDN architecture encompasses multiple elements (NE, SDN controllers, SDN applications, and northbound and southbound interfaces). Therefore, there is a need to protect not only network devices but also controllers, applications, and their communications.  
Figure 2: Relationship between SDN and NFV.  
Prior works [24] have analyzed each component of the SDN architecture using the Microsoft STRIDE methodology and identified potential threats to which they are vulnerable. Table 1 summarizes the potential threats.  
The northbound interface (NBI) presents a significant attack vector due to the multiplicity of APIs employed by SDN controllers. These APIs leverage diverse technologies and languages, such as Python, Java, C, REST, XML, JSON, FTP, LDAP, and others. Exploiting vulnerabilities in any of these technologies or programming languages could grant an attacker control over the SDN network through the compromised controller. For instance, a compromised NBI could enable an attacker to create malicious SDN policies and manipulate the network environment.  
Similarly, the southbound interface (SBI) constitutes a potential attack vector. Numerous APIs and protocols facilitate communication between the controller and network elements. These protocols include OpenFlow, Simple Network Management Protocol (SNMP), Secure Shell (SSH), NETCONF, OVSDB (Open vSwitch Database Management Protocol), OF-Config (OpenFlow Management and Configuration Protocol), etc. While each protocol utilizes its security methods, their relative novelty and potential implementation flaws leave them vulnerable. An attacker could exploit these vulnerabilities to modify or create malicious flows within a device's flow table, enabling the introduction of illegal traffic or the manipulation of routing for malicious purposes, such as Man-in-the-Middle (MITM) attacks.  
The relative novelty of SDN and its software-based infrastructure presents a distinct challenge in terms of security. The lack of a historical record of security incidents hinders our ability to anticipate and proactively address potential attack vectors. This necessitates a proactive approach to network hardening, emphasizing robust security measures across all interfaces and protocols within the SDN architecture.  
To improve the security of SDN networks, several measures can be implemented. A strategy is to secure the controller, which is considered the network's core. So, if this component is compromised, the overall functioning of the network is affected [25]. Another measure is to address the communication bottleneck between the controller and the switches, which can be exploited by attackers [26].