IPinfo IIJ Research & Arrcus NTT Vigil Security, LLC This document specifies how to augment the Routing Policy Specification Language (RPSL) inetnum: class to refer specifically to prefixlen files which are comma-separated values (CSV) files used to specify end-site prefix lengths. This document also describes an optional mechanism that uses the Resource Public Key Infrastructure (RPKI) to authenticate the prefixlen files.