Internet Governance Glossary
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2.4 Critical Internet infrastructure
Collective term for all hardware and software systems that constitute essential components in the operation of the Internet.
Note:
Physical transmission lines of all types, such as wired, fiber optic and microwave links, along with routing equipment, the accompanying critical software services like the Domain Name System (DNS), e-mail, website hosting, authentication and authorization, storage systems, and database servers are considered critical Internet components. If any of these systems and services were to be interrupted for a significant period of time … [t]he Internet...as we know it would collapse