I have a server running CentOS 6 on the bare metal, running the stock CentOS 6 OpenLDAP packages (openldap-2.4.40-16.el6.x86_64, openldap-clients-2.4.40-16.el6.x86_64, openldap-2.4.40-16.el6.i686, openldap-servers-2.4.40-16.el6.x86_64) [yes I know these are old, but they *work* -- "If it ain't broke, don't fix it."]. There are two VMs running on this server, one running Ubuntu 14.04 and the other Ubuntu 18.04. (These two VMs are/will be servers for DRBL.) The Ubuntu 14.04 VM (and all of its diskless clients) are perfectly happy to talk to the OpenLDAP server (slapd) running on the CentOS 6 machine. The Ubuntu 18.04 VM is not. ldapsearch works everywhere though, so it is NOT the server or the core ldap libraries on any of the machines (partitularly the Ubuntu 18.04 VM). I can only assume that there is something fishy with nslcd or the pam/ldap libraries or config on the Ubuntu 18.04 VM. I have checked everything, but I am coming up empty. I am thinking there might be some "trick" to getting LDAP Authentication to work under Ubuntu 18.04 that I am missing.