NORNET CORE is the world's first, open, largescale Internet testbed for multi-homed systems and applications. Particularly, it is currently used for research on topics like multipath transport and resilience. Researchers can run experiments on distributed, programmable nodes that are distributed over various locations and providing access to multiple different Internet service providers (ISP) with different access technologies. Clearly, a key feature of this testbed is to work in the real-world Internet. That is, it is especially desired to expose experiments to real Internet behaviour like background traffic. However, for the researcher, it is necessary to actually know how paths -being used for an experiment -actually behave: Are the paths actually working? How are the round-trip times among sites over different ISPs, etc.. How did the behaviour change over time?To provide such information to the researchers, we have designed and developed a maintenance and monitoring infrastructure for the NORNET CORE testbed. In this paper, we will first introduce this infrastructure. Furthermore, we will demonstrate its usefulness with some useful, real-world examples. Our infrastructure has now become part of the testbed, and it is therefore available for all users of NORNET CORE as well. 1