To enable the LDAP service on an Isilon cluster, the necessary information includes a base distinguished name (base DN), a port number, and at least one LDAP server. These elements are critical in establishing the LDAP service and ensuring it communicates correctly with the directory server. A base DN helps in defining the starting point of the directory tree, the port number identifies the connection route, and the LDAP server acts as the directory server for user and group information.