When you register a domain with 1&1 IONOS, its DNS Settings are already configured for use with 1&1 IONOS applications.
Every domain that you register for the first time with 1&1 IONOS uses the 1&1 IONOS name servers. For security reasons, 1&1 IONOS spreads the name server assignments across multiple name servers. 1&1 IONOS name servers therefore take the following form:
ZZZ represents a number between 016 and 126.