This project modernizes the publicly available DeterLab cybersecurity testbed by: (1) updating the community research infrastructure (switches and nodes) to support large scale, virtualized experiments, (2) streamlining the experimentation process to broaden participation of new user communities. One third of the institutions using DeterLab today are community colleges and smaller universities, which lack dedicated research infrastructure. This new generation of CISE Community Research Infrastructure will offer powerful assistance to level the playing field for the underserved research and student populations. The project will be carried out through a groundbreaking program to: (1) modernize the community research infrastructure of the public DeterLab testbed for cybersecurity experimentation, and to (2) streamline the experimentation process to broaden participation of new user communities. Research infrastructure modernization will be achieved with three architectural changes: (1) replacing current, 15-year old network switches with modern whitebox switches, which support programmable software-defined networking (SDN) and Ethernet Virtual Private Network (EVPN) with Virtual Extensible LAN (VXLAN) dataplane encapsulation, (2) replacing all dated (over 10 years) old PC nodes with 144 high-density nodes, which support virtualization of many nodes on one physical node, (3) replacing current, outdated, testbed software, based on Emulab, with modular and modern Merge software. These changes will modernize the testbed, making it more robust, reliable, and self-sustainable, supporting many more users through resource virtualization. These changes will additionally enable users to perform large-scale experiments with reconfigurable topologies and across multiple testbeds. The project will further streamline the experimentation process on the new Mod DeterLab testbed by: (1) fully integrating several solutions for testbed experimentation (virtualization, traffic generators, orchestration software, malware experimentation environment, etc.), developed over the years, with the mainstream testbed software, documenting them and making them available to all users, (2) providing a set of experiment templates in several cybersecurity domains that users can start from and evolve to fit their needs; these templates will include the newly-integrated experimentation solutions, (3) offering live and recorded Webinars on monthly basis, and offering tutorials and demos at cybersecurity conferences and workshops, as well as diversity conferences and workshops, to attract new users to the modernized DeterLab testbed. Streamlining the experimentation process will make it easier for current users to design and perform experiments, and will attract and ease the on-boarding for new users. Community engagement and outreach activities will ensure that existing and new users provide input to the modernization project.