From 1987 to 1992, Karrenberg worked at the Centrum Wiskunde & Informatica (CWI) in Amsterdam, where he helped to build the central European structured cabling with links to the American NSFNET.
In 1989, Karrenberg was one of the founders of RIPE, the platform for cooperation between European internet providers. In 1992, he was instrumental in founding the world's first Regional Internet Registry, the RIPE NCC, responsible for Europe, the Middle East and parts of Africa and Central Asia, which he headed until 1999.
Karrenberg was the lead scientist at RIPE NCC, leading the way in numerous projects including RIPE Routing Information Service (RIS), RIPE Test Traffic Measurements (TTM), DNS Monitoring Service (DNSMON), and Name Server Daemon (NSD).
- Peter Olsthoorn: Daniel Karrenberg, Duitse netwerkpionier koos jong voor Amsterdam: ‚Direct met Amerikaanse uitvinders communiceren was sensationeel‘.
- Daniel Karrenberg Biography at the website of the Internet Hall of Fame
- Sarah Mitroff: Daniel Karrenberg Helped Bring the Internet to Europe; Now He Keeps It Running.
- Daniel Karrenberg Biography at the website of RIPE