Sun Microsystems This document presents a model for mapping the domain-qualified user and group names used in the Network File System version 4's Access Control List (ACL) entries (ACEs) to internal identifiers such as POSIX UIDs and GIDs, as well as reverse mappings as well as a protocol for effecting such mappings in a consistent way across a server cluster, site, or entire domain. The main goals of this model and protocol are to allow the use of user and group names from multiple domains to be used in POSIX environments as well as enabling multi-protocol fileserver implementations which must support the use of a variety of user and group identifiers.