Defense of United States Infrastructure Act of 2021 This bill sets out programs and requirements related to critical infrastructure and cybersecurity threats, including (1) a pilot program to enable federal and nonfederal entities to share information in order to prevent, identify, and mitigate cyber threats; (2) reporting about the federal government's efforts to support security certifications for information technology; and (3) a working group to develop a strategy for implementing security measures for foundational internet protocols.