RIPE NCC NLNetLabs This document describes an approach to validating the content of the Resource Public Key Infrastructure (RPKI) certificate tree, as it is implemented in the RIPE NCC RPKI Validator. This approach is independent of a particular object retrieval mechanism, which allows it to be used with repositories available over the rsync protocol, the RPKI Repository Delta Protocol (RRDP), and repositories that use a mix of both.