Today, the Belgian research network GIGANET, managed by BELNET, consists of two star-shaped structures, centralized in Brussels, from where data transmission lines depart to national PoPs (point-of-presence), which are located all over the country. Local universities, colleges and other research institutions connect to their nearest PoP. Current capacity is way below predictions for the near future, thus the network needs to be scaled up dramatically. Also, there is a new demand for securely connecting distant institutions, due to several associations between them. We studied the optimal design of the future next-generation network GIGANET2, choosing a new topology, predicting future capacity demands and taking into account real pricing information obtained from telecom companies and optical hardware vendors. The study consisted of involved optimization efforts, and large-scale comparisons of optical hardware and available fiber infrastructure. This work resulted in the design of a physical optical ring topology, together with three network scenarios which are subject to different bandwidth, reliability and cost considerations, closely matching the institutions' requirements. This paper presents the final results of the study.