Question: In a Network Domain Security (NDS) context, what is the primary purpose of dividing an IP-network into security domains, particularly in relation to control plane security?
Option 1: To enhance user data confidentiality across different Radio Access Networks (RANs)
Option 2: To facilitate seamless handovers between different core networks
Option 3: To isolate and protect the control plane of a single operator's core network from external threats using security gateways
Option 4: To optimize IP traffic routing within a single security domain
Explanation: Dividing an NDS/IP-network into security domains, especially for control plane security, is crucial for isolating sensitive core network operations of a single operator. This isolation, achieved through the use of security gateways, protects against external threats and unauthorized access, thereby safeguarding the integrity of the control plane. This approach aligns with best practices in telecom network security, emphasizing the segregation of critical infrastructure components to reduce attack surfaces.