This part of ISO/IEC 27033 describes the threats, design techniques and control issues associated with reference network scenarios. For each scenario, it provides detailed guidance on the security threats and the security design techniques and controls required to mitigate the associated risks. Where relevant, it includes references to ISO/IEC 27033-4 to ISO/IEC 27033-6 to avoid duplicating the content of those documents.The information in this part of ISO/IEC 27033 is for use when reviewing technical security architecture/design options and when selecting and documenting the preferred technical security architecture/design and related security controls, in accordance with ISO/IEC 27033-2. The particular information selected (together with information selected from ISO/IEC 27033-4 to ISO/IEC 27033-6) will depend on the characteristics of the network environment under review, i.e. the particular network scenario(s) and ‘technology’ topic(s) concerned.Overall, this part of ISO/IEC 27033 will aid considerably the comprehensive definition and implementation of security for any organization's network environment.